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page.title=Notepad Tutorial
@jd:body
<p>This tutorial on writing a notepad application gives you a &quot;hands-on&quot; introduction
to the Android framework and the tools you use to build applications on it.
Starting from a preconfigured project file, it guides you through the process of
developing a simple notepad application and provides concrete examples of how to
set up the project, develop the application logic and user interface, and then
compile and run the application. </p>
<p>The tutorial presents the application development as a set of
exercises (see below), each consisting of several steps. You should follow
the steps in each exercise to gradually build and refine your
application. The exercises explain each step in detail and provide all the
sample code you need to complete the application. </p>
<p>When you are finished with the tutorial, you will have created a functioning
Android application and will have learned many of the most important
concepts in Android development. If you want to add more complex features to
your application, you can examine the code in an alternative implementation
of a Note Pad application, in the
<a href="{@docRoot}resources/samples/index.html">Sample Code</a> section. </p>
<a name="who"></a>
<h2>Who Should Use this Tutorial</h2>
<p>This tutorial is designed for experienced developers, especially those with
knowledge of the Java programming language. If you haven't written Java
applications before, you can still use the tutorial, but you might need to work
at a slower pace. </p>
<p>Also note that this tutorial uses
the Eclipse development environment, with the Android plugin installed. If you
are not using Eclipse, you can follow the exercises and build the application,
but you will need to determine how to accomplish the Eclipse-specific
steps in your environment. </p>
<a name="preparing"></a>
<h2>Preparing for the Exercises</h2>
<p>The tutorial assumes that you have some familiarity with basic Android
application concepts and terminology. If you are not, you
should read <a href="{@docRoot}guide/topics/fundamentals.html">Application
Fundamentals</a> before continuing. </p>
<p>This tutorial also builds on the introductory information provided in the
<a href="{@docRoot}resources/tutorials/hello-world.html">Hello World</a>
tutorial, which explains how to set up your Eclipse environment
for building Android applications. We recommend you complete the Hello World
tutorial before starting this one.</p>
<p>To prepare for this lesson:</p>
<ol>
<li>Download the <a href="codelab/NotepadCodeLab.zip">project
exercises archive (.zip)</a>.</li>
<li>Unpack the archive file to a suitable location on your machine.</li>
<li>Open the <code>NotepadCodeLab</code> folder.</li>
</ol>
<p>Inside the <code>NotepadCodeLab</code> folder, you should see six project
files: <code>Notepadv1</code>,
<code>Notepadv2</code>, <code>Notepadv3</code>,
<code>Notepadv1Solution</code>, <code>Notepadv2Solution</code>
and <code>Notepadv3Solution</code>. The <code>Notepadv#</code> projects are
the starting points for each of the exercises, while the
<code>Notepadv#Solution</code> projects are the exercise
solutions. If you are having trouble with a particular exercise, you
can compare your current work against the exercise solution.</p>
<a name="exercises"></a>
<h2> Exercises</h2>
<p>The table below lists the tutorial exercises and describes the development
areas that each covers. Each exercise assumes that you have completed any
previous exercises.</p>
<table border="0" style="padding:4px;spacing:2px;" summary="This
table lists the
tutorial examples and describes what each covers. ">
<tr>
<th width="120"><a href="{@docRoot}resources/tutorials/notepad/notepad-ex1.html">Exercise
1</a></th>
<td>Start here. Construct a simple notes list that lets the user add new notes but not
edit them. Demonstrates the basics of <code>ListActivity</code> and creating
and handling
menu options. Uses a SQLite database to store the notes.</td>
</tr>
<tr>
<th><a href="{@docRoot}resources/tutorials/notepad/notepad-ex2.html">Exercise 2</a></th>
<td>Add a second Activity to the
application. Demonstrates constructing a
new Activity, adding it to the Android manifest, passing data between the
activities, and using more advanced screen layout. Also shows how to
invoke another Activity to return a result, using
<code>startActivityForResult()</code>.</td>
</tr>
<tr>
<th><a href="{@docRoot}resources/tutorials/notepad/notepad-ex3.html">Exercise 3</a></th>
<td>Add handling of life-cycle events to
the application, to let it
maintain application state across the life cycle. </td>
</tr>
<tr>
<th><a href="{@docRoot}resources/tutorials/notepad/notepad-extra-credit.html">Extra
Credit</a></th>
<td>Demonstrates how to use the Eclipse
debugger and how you can use it to
view life-cycle events as they are generated. This section is optional but
highly recommended.</td>
</tr>
</table>
<a name="other"></a>
<h2>Other Resources and Further Learning</h2>
<ul>
<li>For a lighter but broader introduction to concepts not covered in the
tutorial,
take a look at <a href="{@docRoot}resources/faq/commontasks.html">Common Android Tasks</a>.</li>
<li>The Android SDK includes a variety of fully functioning sample applications
that make excellent opportunities for further learning. You can find the sample
applications in the <code>samples/</code> directory of your downloaded SDK, or browser them
here, in the <a href="{@docRoot}resources/samples/index.html">Sample Code</a> section.</li>
<li>This tutorial draws from the full Notepad application included in the
<code>samples/</code> directory of the SDK, though it does not match it exactly.
When you are done with the tutorial,
it is highly recommended that you take a closer look at this version of the Notepad
application,
as it demonstrates a variety of interesting additions for your application,
such as:</li>
<ul>
<li>Setting up a custom striped list for the list of notes.</li>
<li>Creating a custom text edit view that overrides the <code>draw()</code>
method to make it look like a lined notepad.</li>
<li>Implementing a full <code>ContentProvider</code> for notes.</li>
<li>Reverting and discarding edits instead of just automatically saving
them.</li>
</ul>
</ul>

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page.title=Notepad Exercise 1
parent.title=Notepad Tutorial
parent.link=index.html
@jd:body
<p><em>In this exercise, you will construct a simple notes list that lets the
user add new notes but not edit them. The exercise demonstrates:</em></p>
<ul>
<li><em>The basics of <code>ListActivities</code> and creating and handling menu
options. </em></li>
<li><em>How to use a SQLite database to store the notes.</em></li>
<li><em>How to bind data from a database cursor into a ListView using a
SimpleCursorAdapter.</em></li>
<li><em>The basics of screen layouts, including how to lay out a list view, how
you can add items to the activity menu, and how the activity handles those menu
selections. </em></li>
</ul>
<div style="float:right;white-space:nowrap">
<span style="color:#BBB;">
[<a href="notepad-ex1.html" style="color:#BBB;">Exercise 1</a>]</span>
[<a href="notepad-ex2.html">Exercise 2</a>]
[<a href="notepad-ex3.html">Exercise 3</a>]
[<a href="notepad-extra-credit.html">Extra Credit</a>]
</div>
<h2>Step 1</h2>
<p>Open up the <code>Notepadv1</code> project in Eclipse.</p>
<p><code>Notepadv1</code> is a project that is provided as a starting point. It
takes care of some of the boilerplate work that you have already seen if you
followed the <a href="{@docRoot}resources/tutorials/hello-world.html">Hello,
World</a> tutorial.</p>
<ol>
<li>
Start a new Android Project by clicking <strong>File</strong> >
<strong>New</strong> > <strong>Android Project</strong>.</li>
<li>
In the New Android Project dialog, select <strong>Create project from existing source</strong>.</li>
<li>
Click <strong>Browse</strong> and navigate to where you copied the <code>NotepadCodeLab</code>
(downloaded during <a href="{@docRoot}resources/tutorials/notepad/index.html#preparing">setup</a>)
and select <code>Notepadv1</code>.</li>
<li>
The Project Name and other properties should be automatically filled for you.
You must select the Build Target&mdash;we recommend selecting a target with the
lowest platform version available. Also add an integer to the Min SDK Version field
that matches the API Level of the selected Build Target.</li>
<li>
Click <strong>Finish</strong>. The <code>Notepadv1</code> project should open and be
visible in your Eclipse package explorer.</li>
</ol>
<p>If you see an error about <code>AndroidManifest.xml</code>, or some
problems related to an Android zip file, right click on the project and
select <strong>Android Tools</strong> > <strong>Fix Project Properties</strong>.
(The project is looking in the wrong location for the library file,
this will fix it for you.)</p>
<h2>Step 2</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Accessing and modifying data</h2>
<p>For this
exercise, we are using a SQLite database to store our data. This is useful
if only <em>your</em> application will need to access or modify the data. If you wish for
other activities to access or modify the data, you have to expose the data using a
{@link android.content.ContentProvider ContentProvider}.</p>
<p>If you are interested, you can find out more about
<a href="{@docRoot}guide/topics/providers/content-providers.html">content providers</a> or the
whole
subject of <a href="{@docRoot}guide/topics/data/data-storage.html">Data Storage</a>.
The NotePad sample in the <code>samples/</code> folder of the SDK also has an example of how
to create a ContentProvider.</p>
</div>
</div>
<p>Take a look at the <code>NotesDbAdapter</code> class &mdash; this class is provided to
encapsulate data access to a SQLite database that will hold our notes data
and allow us to update it.</p>
<p>At the top of the class are some constant definitions that will be used in the application
to look up data from the proper field names in the database. There is also a database creation
string defined, which is used to create a new database schema if one doesn't exist already.</p>
<p>Our database will have the name <code>data</code>, and have a single table called
<code>notes</code>, which in turn has three fields: <code>_id</code>, <code>title</code> and
<code>body</code>. The <code>_id</code> is named with an underscore convention used in a number of
places inside the Android SDK and helps keep a track of state. The <code>_id</code>
usually has to be specified when querying or updating the database (in the column projections
and so on). The other two fields are simple text fields that will store data.
</p>
<p>The constructor for <code>NotesDbAdapter</code> takes a Context, which allows it to communicate with aspects
of the Android operating system. This is quite common for classes that need to touch the
Android system in some way. The Activity class implements the Context class, so usually you will just pass
<code>this</code> from your Activity, when needing a Context.</p>
<p>The <code>open()</code> method calls up an instance of DatabaseHelper, which is our local
implementation of the SQLiteOpenHelper class. It calls <code>getWritableDatabase()</code>,
which handles creating/opening a database for us.</p>
<p><code>close()</code> just closes the database, releasing resources related to the
connection.</p>
<p><code>createNote()</code> takes strings for the title and body of a new note,
then creates that note in the database. Assuming the new note is created successfully, the
method also returns the row <code>_id</code> value for the newly created note.</p>
<p><code>deleteNote()</code> takes a <var>rowId</var> for a particular note, and deletes that note from
the database.</p>
<p><code>fetchAllNotes()</code> issues a query to return a {@link android.database.Cursor} over all notes in the
database. The <code>query()</code> call is worth examination and understanding. The first field is the
name of the database table to query (in this case <code>DATABASE_TABLE</code> is "notes").
The next is the list of columns we want returned, in this case we want the <code>_id</code>,
<code>title</code> and <code>body</code> columns so these are specified in the String array.
The remaining fields are, in order: <code>selection</code>,
<code>selectionArgs</code>, <code>groupBy</code>, <code>having</code> and <code>orderBy</code>.
Having these all <code>null</code> means we want all data, need no grouping, and will take the default
order. See {@link android.database.sqlite.SQLiteDatabase SQLiteDatabase} for more details.</p>
<p class="note"><b>Note:</b> A Cursor is returned rather than a collection of rows. This allows
Android to use resources efficiently -- instead of putting lots of data straight into memory
the cursor will retrieve and release data as it is needed, which is much more efficient for
tables with lots of rows.</p>
<p><code>fetchNote()</code> is similar to <code>fetchAllNotes()</code> but just gets one note
with the <var>rowId</var> we specify. It uses a slightly different version of the
{@link android.database.sqlite.SQLiteDatabase} <code>query()</code> method.
The first parameter (set <em>true</em>) indicates that we are interested
in one distinct result. The <var>selection</var> parameter (the fourth parameter) has been specified to search
only for the row "where _id =" the <var>rowId</var> we passed in. So we are returned a Cursor on
the one row.</p>
<p>And finally, <code>updateNote()</code> takes a <var>rowId</var>, <var>title</var> and <var>body</var>, and uses a
{@link android.content.ContentValues ContentValues} instance to update the note of the given
<var>rowId</var>.</p>
<h2 style="clear:right;">Step 3</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Layouts and activities</h2>
<p>Most Activity classes will have a layout associated with them. The layout
will be the "face" of the Activity to the user. In this case our layout will
take over the whole screen and provide a list of notes.</p>
<p>Full screen layouts are not the only option for an Activity however. You
might also want to use a <a
href="{@docRoot}resources/faq/commontasks.html#floatingorfull">floating
layout</a> (for example, a <a
href="{@docRoot}resources/faq/commontasks.html#dialogsandalerts">dialog
or alert</a>),
or perhaps you don't need a layout at all (the Activity will be invisible
to the user unless you specify some kind of layout for it to use).</p>
</div>
</div>
<p>Open the <code>notepad_list.xml</code> file in <code>res/layout</code>
and
take a look at it. (You may have to
hit the <em>xml</em> tab, at the bottom, in order to view the XML markup.)</p>
<p>This is a mostly-empty layout definition file. Here are some
things you should know about a layout file:</p>
<ul>
<li>
All Android layout files must start with the XML header line:
<code>&lt;?xml version="1.0" encoding="utf-8"?&gt;</code>. </li>
<li>
The next definition will often (but not always) be a layout
definition of some kind, in this case a <code>LinearLayout</code>. </li>
<li>
The XML namespace of Android should always be defined in
the top level component or layout in the XML so that <code>android:</code> tags can
be used through the rest of the file:
<p><code>xmlns:android="http://schemas.android.com/apk/res/android"</code></p>
</li>
</ul>
<h2 style="clear:right;">Step 4</h2>
<p>We need to create the layout to hold our list. Add code inside
of the <code>LinearLayout</code> element so the whole file looks like this: </p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;LinearLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;wrap_content&quot;
android:layout_height=&quot;wrap_content&quot;&gt;
&lt;ListView android:id=&quot;@android:id/list&quot;
android:layout_width=&quot;wrap_content&quot;
android:layout_height=&quot;wrap_content&quot;/&gt;
&lt;TextView android:id=&quot;@android:id/empty&quot;
android:layout_width=&quot;wrap_content&quot;
android:layout_height=&quot;wrap_content&quot;
android:text=&quot;@string/no_notes&quot;/&gt;
&lt;/LinearLayout&gt;
</pre>
<ul>
<li>
The <strong>&#64;</strong> symbol in the id strings of the <code>ListView</code> and
<code>TextView</code> tags means
that the XML parser should parse and expand the rest of
the id string and use an ID resource.</li>
<li>
The <code>ListView</code> and <code>TextView</code> can be
thought as two alternative views, only one of which will be displayed at once.
ListView will be used when there are notes to be shown, while the TextView
(which has a default value of "No Notes Yet!" defined as a string
resource in <code>res/values/strings.xml</code>) will be displayed if there
aren't any notes to display.</li>
<li>The <code>list</code> and <code>empty</code> IDs are
provided for us by the Android platform, so, we must
prefix the <code>id</code> with <code>android:</code> (e.g., <code>@android:id/list</code>).</li>
<li>The View with the <code>empty</code> id is used
automatically when the {@link android.widget.ListAdapter} has no data for the ListView. The
ListAdapter knows to look for this name by default. Alternatively, you could change the
default empty view by using {@link android.widget.AdapterView#setEmptyView(View)}
on the ListView.
<p>
More broadly, the <code>android.R</code> class is a set of predefined
resources provided for you by the platform, while your project's
<code>R</code> class is the set of resources your project has defined.
Resources found in the <code>android.R</code> resource class can be
used in the XML files by using the <code>android:</code> name space prefix
(as we see here).</p>
</li>
</ul>
<h2 style="clear:right;">Step 5</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Resources and the R class</h2>
<p>The folders under res/ in the Eclipse project are for resources.
There is a <a href="{@docRoot}resources/faq/commontasks.html#filelist">specific structure</a>
to the
folders and files under res/.</p>
<p>Resources defined in these folders and files will have
corresponding entries in the R class allowing them to be easily accessed
and used from your application. The R class is automatically generated using the contents
of the res/ folder by the eclipse plugin (or by aapt if you use the command line tools).
Furthermore, they will be bundled and deployed for you as part of the application.</p>
</p>
</div>
</div>
<p>To make the list of notes in the ListView, we also need to define a View for each row:</p>
<ol>
<li>
Create a new file under <code>res/layout</code> called
<code>notes_row.xml</code>. </li>
<li>
Add the following contents (note: again the XML header is used, and the
first node defines the Android XML namespace)<br>
<pre style="overflow:auto">
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;TextView android:id=&quot;&#64;+id/text1&quot;
xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;wrap_content&quot;
android:layout_height=&quot;wrap_content&quot;/&gt;</pre>
<p>
This is the View that will be used for each notes title row &mdash; it has only
one text field in it. </p>
<p>In this case we create a new id called <code>text1</code>. The
<strong>+</strong> after the <strong>@</strong> in the id string indicates that the id should
be automatically created as a resource if it does not already exist, so we are defining
<code>text1</code> on the fly and then using it.</p>
</li>
<li>Save the file.</li>
</ol>
<p>Open the <code>R.java</code> class in the
project and look at it, you should see new definitions for
<code>notes_row</code> and <code>text1</code> (our new definitions)
meaning we can now gain access to these from the our code. </p>
<h2 style="clear:right;">Step 6</h2>
<p>Next, open the <code>Notepadv1</code> class in the source. In the following steps, we are going to
alter this class to become a list adapter and display our notes, and also
allow us to add new notes.</p>
<p><code>Notepadv1</code> will inherit from a subclass
of <code>Activity</code> called a <code>ListActivity</code>,
which has extra functionality to accommodate the kinds of
things you might want to do with a list, for
example: displaying an arbitrary number of list items in rows on the screen,
moving through the list items, and allowing them to be selected.</p>
<p>Take a look through the existing code in <code>Notepadv1</code> class.
There is a currently an unused private field called <code>mNoteNumber</code> that
we will use to create numbered note titles.</p>
<p>There are also three override methods defined:
<code>onCreate</code>, <code>onCreateOptionsMenu</code> and
<code>onOptionsItemSelected</code>; we need to fill these
out:</p>
<ul>
<li><code>onCreate()</code> is called when the activity is
started &mdash; it is a little like the "main" method for an Activity. We use
this to set up resources and state for the activity when it is
running.</li>
<li><code>onCreateOptionsMenu()</code> is used to populate the
menu for the Activity. This is shown when the user hits the menu button,
and
has a list of options they can select (like "Create
Note"). </li>
<li><code>onOptionsItemSelected()</code> is the other half of the
menu equation, it is used to handle events generated from the menu (e.g.,
when the user selects the "Create Note" item).
</li>
</ul>
<h2>Step 7</h2>
<p>Change the inheritance of <code>Notepadv1</code> from
<code>Activity</code>
to <code>ListActivity</code>:</p>
<pre>public class Notepadv1 extends ListActivity</pre>
<p>Note: you will have to import <code>ListActivity</code> into the
Notepadv1
class using Eclipse, <strong>ctrl-shift-O</strong> on Windows or Linux, or
<strong>cmd-shift-O</strong> on the Mac (organize imports) will do this for you
after you've written the above change.</p>
<h2>Step 8</h2>
<p>Fill out the body of the <code>onCreate()</code> method.</p>
<p>Here we will set the title for the Activity (shown at the top of the
screen), use the <code>notepad_list</code> layout we created in XML,
set up the <code>NotesDbAdapter</code> instance that will
access notes data, and populate the list with the available note
titles:</p>
<ol>
<li>
In the <code>onCreate</code> method, call <code>super.onCreate()</code> with the
<code>savedInstanceState</code> parameter that's passed in.</li>
<li>
Call <code>setContentView()</code> and pass <code>R.layout.notepad_list</code>.</li>
<li>
At the top of the class, create a new private class field called <code>mDbHelper</code> of class
<code>NotesDbAdapter</code>.
</li>
<li>
Back in the <code>onCreate</code> method, construct a new
<code>NotesDbAdapter</code>
instance and assign it to the <code>mDbHelper</code> field (pass
<code>this</code> into the constructor for <code>DBHelper</code>)
</li>
<li>
Call the <code>open()</code> method on <code>mDbHelper</code> to open (or create) the
database.
</li>
<li>
Finally, call a new method <code>fillData()</code>, which will get the data and
populate the ListView using the helper &mdash; we haven't defined this method yet. </li>
</ol>
<p>
<code>onCreate()</code> should now look like this:</p>
<pre>
&#64;Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.notepad_list);
mDbHelper = new NotesDbAdapter(this);
mDbHelper.open();
fillData();
}</pre>
<p>And be sure you have the <code>mDbHelper</code> field definition (right
under the mNoteNumber definition): </p>
<pre> private NotesDbAdapter mDbHelper;</pre>
<h2>Step 9</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>More about menus</h2>
<p>The notepad application we are constructing only scratches the
surface with <a href="{@docRoot}resources/faq/commontasks.html#addmenuitems">menus</a>. </p>
<p>You can also <a href="{@docRoot}resources/faq/commontasks.html#menukeyshortcuts">add
shortcut keys for menu items</a>, <a
href="{@docRoot}resources/faq/commontasks.html#menukeyshortcuts">create
submenus</a> and even <a href="{@docRoot}resources/faq/commontasks.html#addingtoothermenus">add
menu items to other applications!</a>. </p>
</div>
</div>
<p>Fill out the body of the <code>onCreateOptionsMenu()</code> method.</p>
<p>We will now create the "Add Item" button that can be accessed by pressing the menu
button on the device. We'll specify that it occupy the first position in the menu.</p>
<ol>
<li>
In <code>strings.xml</code> resource (under <code>res/values</code>), add
a new string named "menu_insert" with its value set to <code>Add Item</code>:
<pre>&lt;string name="menu_insert"&gt;Add Item&lt;/string&gt;</pre>
<p>Then save the file and return to <code>Notepadv1</code>.</p>
</li>
<li>Create a menu position constant at the top of the class:
<pre>public static final int INSERT_ID = Menu.FIRST;</pre>
</li>
<li>In the <code>onCreateOptionsMenu()</code> method, change the
<code>super</code> call so we capture the boolean return as <code>result</code>. We'll return this value at the end.</li>
<li>Then add the menu item with <code>menu.add()</code>.</li>
</ol>
<p>The whole method should now look like this:
<pre>
&#64;Override
public boolean onCreateOptionsMenu(Menu menu) {
boolean result = super.onCreateOptionsMenu(menu);
menu.add(0, INSERT_ID, 0, R.string.menu_insert);
return result;
}</pre>
<p>The arguments passed to <code>add()</code> indicate: a group identifier for this menu (none,
in this case), a unique ID (defined above), the order of the item (zero indicates no preference),
and the resource of the string to use for the item.</p>
<h2 style="clear:right;">Step 10</h2>
<p>Fill out the body of the <code>onOptionsItemSelected()</code> method:</p>
<p>This is going
to handle our new "Add Note" menu item. When this is selected, the
<code>onOptionsItemSelected()</code> method will be called with the
<code>item.getId()</code> set to <code>INSERT_ID</code> (the constant we
used to identify the menu item). We can detect this, and take the
appropriate actions:</p>
<ol>
<li>
The <code>super.onOptionsItemSelected(item)</code> method call goes at the
end of this method &mdash; we want to catch our events first! </li>
<li>
Write a switch statement on <code>item.getItemId()</code>.
<p>In the case of <var>INSERT_ID</var>, call a new method, <code>createNote()</code>,
and return true, because we have handled this event and do not want to
propagate it through the system.</p>
</li>
<li>Return the result of the superclass' <code>onOptionsItemSelected()</code>
method at the end.</li>
</ol>
<p>
The whole <code>onOptionsItemSelect()</code> method should now look like
this:</p>
<pre>
&#64;Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case INSERT_ID:
createNote();
return true;
}
return super.onOptionsItemSelected(item);
}</pre>
<h2>Step 11</h2>
<p>Add a new <code>createNote()</code> method:</p>
<p>In this first version of
our application, <code>createNote()</code> is not going to be very useful.
We will simply
create a new note with a title assigned to it based on a counter ("Note 1",
"Note 2"...) and with an empty body. At present we have no way of editing
the contents of a note, so for now we will have to be content making one
with some default values:</p>
<ol>
<li>Construct the name using "Note" and the counter we defined in the class: <code>
String noteName = "Note " + mNoteNumber++</code></li>
<li>
Call <code>mDbHelper.createNote()</code> using <code>noteName</code> as the
title and <code>""</code> for the body
</li>
<li>
Call <code>fillData()</code> to populate the list of notes (inefficient but
simple) &mdash; we'll create this method next.</li>
</ol>
<p>
The whole <code>createNote()</code> method should look like this: </p>
<pre>
private void createNote() {
String noteName = &quot;Note &quot; + mNoteNumber++;
mDbHelper.createNote(noteName, &quot;&quot;);
fillData();
}</pre>
<h2>Step 12</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>List adapters</h2>
<p>Our example uses a {@link android.widget.SimpleCursorAdapter
SimpleCursorAdapter} to bind a database {@link android.database.Cursor Cursor}
into a ListView, and this is a common way to use a {@link android.widget.ListAdapter
ListAdapter}. Other options exist like {@link android.widget.ArrayAdapter ArrayAdapter} which
can be used to take a List or Array of in-memory data and bind it in to
a list as well.</p>
</div>
</div>
<p>Define the <code>fillData()</code> method:</p>
<p>This
method uses <code>SimpleCursorAdapter,</code> which takes a database <code>Cursor</code>
and binds it to fields provided in the layout. These fields define the row elements of our list
(in this case we use the <code>text1</code> field in our
<code>notes_row.xml</code> layout), so this allows us to easily populate the list with
entries from our database.</p>
<p>To do this we have to provide a mapping from the <code>title</code> field in the returned Cursor, to
our <code>text1</code> TextView, which is done by defining two arrays: the first a string array
with the list of columns to map <em>from</em> (just "title" in this case, from the constant
<code>NotesDbAdapter.KEY_TITLE</code>) and, the second, an int array
containing references to the views that we'll bind the data <em>into</em>
(the <code>R.id.text1</code> TextView).</p>
<p>This is a bigger chunk of code, so let's first take a look at it:</p>
<pre>
private void fillData() {
// Get all of the notes from the database and create the item list
Cursor c = mDbHelper.fetchAllNotes();
startManagingCursor(c);
String[] from = new String[] { NotesDbAdapter.KEY_TITLE };
int[] to = new int[] { R.id.text1 };
// Now create an array adapter and set it to display using our row
SimpleCursorAdapter notes =
new SimpleCursorAdapter(this, R.layout.notes_row, c, from, to);
setListAdapter(notes);
}</pre>
<p>Here's what we've done:</p>
<ol>
<li>
After obtaining the Cursor from <code>mDbHelper.fetchAllNotes()</code>, we
use an Activity method called
<code>startManagingCursor()</code> that allows Android to take care of the
Cursor lifecycle instead of us needing to worry about it. (We will cover the implications
of the lifecycle in exercise 3, but for now just know that this allows Android to do some
of our resource management work for us.)</li>
<li>
Then we create a string array in which we declare the column(s) we want
(just the title, in this case), and an int array that defines the View(s)
to which we'd like to bind the columns (these should be in order, respective to
the string array, but here we only have one for each).</li>
<li>
Next is the SimpleCursorAdapter instantiation.
Like many classes in Android, the SimpleCursorAdapter needs a Context in order to do its
work, so we pass in <code>this</code> for the context (since subclasses of Activity
implement Context). We pass the <code>notes_row</code> View we created as the receptacle
for the data, the Cursor we just created, and then our arrays.</li>
</ol>
<p>
In the future, remember that the mapping between the <strong>from</strong> columns and <strong>to</strong> resources
is done using the respective ordering of the two arrays. If we had more columns we wanted
to bind, and more Views to bind them in to, we would specify them in order, for example we
might use <code>{ NotesDbAdapter.KEY_TITLE, NotesDbAdapter.KEY_BODY }</code> and
<code>{ R.id.text1, R.id.text2 }</code> to bind two fields into the row (and we would also need
to define text2 in the notes_row.xml, for the body text). This is how you can bind multiple fields
into a single row (and get a custom row layout as well).</p>
<p>
If you get compiler errors about classes not being found, ctrl-shift-O or
(cmd-shift-O on the mac) to organize imports.
</p>
<h2 style="clear:right;">Step 13</h2>
<p>Run it!
<ol>
<li>
Right click on the <code>Notepadv1</code> project.</li>
<li>
From the popup menu, select <strong>Run As</strong> &gt;
<strong>Android Application</strong>.</li>
<li>
If you see a dialog come up, select Android Launcher as the way of running
the application (you can also use the link near the top of the dialog to
set this as your default for the workspace; this is recommended as it will
stop the plugin from asking you this every time).</li>
<li>Add new notes by hitting the menu button and selecting <em>Add
Item</em> from the menu.</li>
</ol>
<h2 style="clear:right;">Solution and Next Steps</h2>
<p>You can see the solution to this class in <code>Notepadv1Solution</code>
from
the zip file to compare with your own.</p>
<p>Once you are ready, move on to <a href="notepad-ex2.html">Tutorial
Exercise 2</a> to add the ability to create, edit and delete notes.</p>

641
base/docs/html/guide/tutorials/notepad/notepad-ex2.jd Normal file
View File

@@ -0,0 +1,641 @@
Rpage.title=Notepad Exercise 2
parent.title=Notepad Tutorial
parent.link=index.html
@jd:body
<p><em>In this exercise, you will add a second Activity to your notepad application, to let the user
create and edit notes. You will also allow the user to delete existing notes through a context menu.
The new Activity assumes responsibility for creating new notes by
collecting user input and packing it into a return Bundle provided by the intent. This exercise
demonstrates:</em></p>
<ul>
<li><em>Constructing a new Activity and adding it to the Android manifest</em></li>
<li><em>Invoking another Activity asynchronously using <code>startActivityForResult()</code></em></li>
<li><em>Passing data between Activity in Bundle objects</em></li>
<li><em>How to use a more advanced screen layout</em></li>
<li><em>How to create a context menu</em></li>
</ul>
<div style="float:right;white-space:nowrap">
[<a href="notepad-ex1.html">Exercise 1</a>]
<span style="color:#BBB;">
[<a href="notepad-ex2.html" style="color:#DDD;">Exercise 2</a>]
</span>
[<a href="notepad-ex3.html">Exercise 3</a>]
[<a href="notepad-extra-credit.html">Extra Credit</a>]
</div>
<h2>Step 1</h2>
<p>Create a new Android project using the sources from <code>Notepadv2</code> under the
<code>NotepadCodeLab</code> folder, just like you did for the first exercise. If you see an error about
<code>AndroidManifest.xml</code>, or some problems related to an
<code>android.zip</code> file, right click on the project and select <strong>Android
Tools</strong> &gt; <strong>Fix Project Properties</strong>.</p>
<p>Open the <code>Notepadv2</code> project and take a look around:</p>
<ul>
<li>
Open and look at the <code>strings.xml</code> file under
<code>res/values</code> &mdash; there are several new strings which we will use
for our new functionality
</li>
<li>
Also, open and take a look at the top of the <code>Notepadv2</code> class,
you will notice several new constants have been defined along with a new <code>mNotesCursor</code>
field used to hold the cursor we are using.
</li>
<li>
Note also that the <code>fillData()</code> method has a few more comments and now uses
the new field to store the notes Cursor. The <code>onCreate()</code> method is
unchanged from the first exercise. Also notice that the member field used to store the
notes Cursor is now called <code>mNotesCursor</code>. The <code>m</code> denotes a member
field and is part of the Android coding style standards.
</li>
<li>
There are also a couple of new overridden methods
(<code>onCreateContextMenu()</code>, <code>onContextItemSelected()</code>,
<code>onListItemClick()</code> and <code>onActivityResult()</code>)
which we will be filling in below.
</li>
</ul>
<h2>Step 2</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<p>Context menus should always be used when performing actions upon specific elements in the UI.
When you register a View to a context menu, the context menu is revealed by performing a "long-click"
on the UI component (press and hold the touchscreen or highlight and hold down the selection key for about two seconds).</p>
</div>
</div>
<p>First, let's create the context menu that will allow users to delete individual notes.
Open the Notepadv2 class.</p>
<ol>
<li>In order for each list item in the ListView to register for the context menu, we call
<code>registerForContextMenu()</code> and pass it our ListView. So, at the very end of
the <code>onCreate()</code> method add this line:
<pre>registerForContextMenu(getListView());</pre>
<p>Because our Activity extends the ListActivity class, <code>getListView()</code> will return us
the local ListView object for the Activity. Now, each list item in this ListView will activate the
context menu.
<li>
Now fill in the <code>onCreateContextMenu()</code> method. This callback is similar to the other
menu callback used for the options menu. Here, we add just one line, which will add a menu item
to delete a note. Call <code>menu.add()</code> like so:
<pre>
public boolean onCreateContextMenu(Menu menu, View v
ContextMenuInfo menuInfo) {
super.onCreateContextMenu(menu, v, menuInfo);
menu.add(0, DELETE_ID, 0, R.string.menu_delete);
}</pre>
<p>The <code>onCreateContextMenu()</code> callback passes some other information in addition to the Menu object,
such as the View that has been triggered for the menu and
an extra object that may contain additional information about the object selected. However, we don't care about
these here, because we only have one kind of object in the Activity that uses context menus. In the next
step, we'll handle the menu item selection.</p>
</li>
</ol>
<h2>Step 3</h2>
<p>Now that the we've registered our ListView for a context menu and defined our context menu item, we need
to handle the callback when it is selected. For this, we need to identify the list ID of the
selected item, then delete it. So fill in the
<code>onContextItemSelected()</code> method like this:</p>
<pre>
public boolean onContextItemSelected(MenuItem item) {
switch(item.getItemId()) {
case DELETE_ID:
AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
mDbHelper.deleteNote(info.id);
fillData();
return true;
}
return super.onContextItemSelected(item);
}</pre>
<p>Here, we retrieve the {@link android.widget.AdapterView.AdapterContextMenuInfo AdapterContextMenuInfo}
with {@link android.view.MenuItem#getMenuInfo()}. The <var>id</var> field of this object tells us
the position of the item in the ListView. We then pass this to the <code>deleteNote()</code>
method of our NotesDbAdapter and the note is deleted. That's it for the context menu &mdash; notes
can now be deleted.</p>
<h2 style="clear:right;">Step 4</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Starting Other Activities</h2>
<p>In this example our Intent uses a class name specifically.
As well as
<a href="{@docRoot}resources/faq/commontasks.html#intentexamples">starting intents</a> in
classes we already know about, be they in our own application or another
application, we can also create Intents without knowing exactly which
application will handle it.</p>
<p>For example, we might want to open a page in a
browser, and for this we still use
an Intent. But instead of specifying a class to handle it, we use
a predefined Intent constant, and a content URI that describes what we
want to do. See {@link android.content.Intent
android.content.Intent} for more information.</p>
</div>
</div>
<p>Fill in the body of the <code>createNote()</code> method:
<p>Create a new <code>Intent</code> to create a note
(<code>ACTIVITY_CREATE</code>) using the <code>NoteEdit</code> class.
Then fire the Intent using the <code>startActivityForResult()</code> method
call:</p>
<pre style="overflow:auto">
Intent i = new Intent(this, NoteEdit.class);
startActivityForResult(i, ACTIVITY_CREATE);</pre>
<p>This form of the Intent call targets a specific class in our Activity, in this case
<code>NoteEdit</code>. Since the Intent class will need to communicate with the Android
operating system to route requests, we also have to provide a Context (<code>this</code>).</p>
<p>The <code>startActivityForResult()</code> method fires the Intent in a way that causes a method
in our Activity to be called when the new Activity is completed. The method in our Activity
that receives the callback is called
<code>onActivityResult()</code> and we will implement it in a later step. The other way
to call an Activity is using <code>startActivity()</code> but this is a "fire-and-forget" way
of calling it &mdash; in this manner, our Activity is not informed when the Activity is completed, and there is
no way to return result information from the called Activity with <code>startActivity()</code>.
<p>Don't worry about the fact that <code>NoteEdit</code> doesn't exist yet,
we will fix that soon. </p>
</li>
<h2>Step 5</h2>
<p>Fill in the body of the <code>onListItemClick()</code> override.</p>
<p><code>onListItemClick()</code> is a callback method that we'll override. It is called when
the user selects an item from the list. It is passed four parameters: the
<code>ListView</code> object it was invoked from, the <code>View</code>
inside the <code>ListView</code> that was clicked on, the
<code>position</code> in the list that was clicked, and the
<code>mRowId</code> of the item that was clicked. In this instance we can
ignore the first two parameters (we only have one <code>ListView</code> it
could be), and we ignore the <code>mRowId</code> as well. All we are
interested in is the <code>position</code> that the user selected. We use
this to get the data from the correct row, and bundle it up to send to
the <code>NoteEdit</code> Activity.</p>
<p>In our implementation of the callback, the method creates an
<code>Intent</code> to edit the note using
the <code>NoteEdit</code> class. It then adds data into the extras Bundle of
the Intent, which will be passed to the called Activity. We use it
to pass in the title and body text, and the <code>mRowId</code> for the note we are
editing. Finally, it will fire the Intent using the
<code>startActivityForResult()</code> method call. Here's the code that
belongs in <code>onListItemClick()</code>:</p>
<pre>
super.onListItemClick(l, v, position, id);
Cursor c = mNotesCursor;
c.moveToPosition(position);
Intent i = new Intent(this, NoteEdit.class);
i.putExtra(NotesDbAdapter.KEY_ROWID, id);
i.putExtra(NotesDbAdapter.KEY_TITLE, c.getString(
c.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));
i.putExtra(NotesDbAdapter.KEY_BODY, c.getString(
c.getColumnIndexOrThrow(NotesDbAdapter.KEY_BODY)));
startActivityForResult(i, ACTIVITY_EDIT);</pre>
<ul>
<li>
<code>putExtra()</code> is the method to add items into the extras Bundle
to pass in to intent invocations. Here, we are
using the Bundle to pass in the title, body and mRowId of the note we want to edit.
</li>
<li>
The details of the note are pulled out from our query Cursor, which we move to the
proper position for the element that was selected in the list, with
the <code>moveToPosition()</code> method.</li>
<li>With the extras added to the Intent, we invoke the Intent on the
<code>NoteEdit</code> class by passing <code>startActivityForResult()</code>
the Intent and the request code. (The request code will be
returned to <code>onActivityResult</code> as the <code>requestCode</code> parameter.)</li>
</ul>
<p class="note"><b>Note:</b> We assign the mNotesCursor field to a local variable at the
start of the method. This is done as an optimization of the Android code. Accessing a local
variable is much more efficient than accessing a field in the Dalvik VM, so by doing this
we make only one access to the field, and five accesses to the local variable, making the
routine much more efficient. It is recommended that you use this optimization when possible.</p>
<h2>Step 6</h2>
<p>The above <code>createNote()</code> and <code>onListItemClick()</code>
methods use an asynchronous Intent invocation. We need a handler for the callback, so here we fill
in the body of the <code>onActivityResult()</code>. </p>
<p><code>onActivityResult()</code> is the overridden method
which will be called when an Activity returns with a result. (Remember, an Activity
will only return a result if launched with <code>startActivityForResult</code>.) The parameters provided
to the callback are: </p>
<ul>
<li><code>requestCode</code> &mdash; the original request code
specified in the Intent invocation (either <code>ACTIVITY_CREATE</code> or
<code>ACTIVITY_EDIT</code> for us).
</li>
<li><code>resultCode</code> &mdash; the result (or error code) of the call, this
should be zero if everything was OK, but may have a non-zero code indicating
that something failed. There are standard result codes available, and you
can also create your own constants to indicate specific problems.
</li>
<li><code>intent</code> &mdash; this is an Intent created by the Activity returning
results. It can be used to return data in the Intent "extras."
</li>
</ul>
<p>The combination of <code>startActivityForResult()</code> and
<code>onActivityResult()</code> can be thought of as an asynchronous RPC
(remote procedure call) and forms the recommended way for an Activity to invoke
another and share services.</p>
<p>Here's the code that belongs in your <code>onActivityResult()</code>:</p>
<pre>
super.onActivityResult(requestCode, resultCode, intent);
Bundle extras = intent.getExtras();
switch(requestCode) {
case ACTIVITY_CREATE:
String title = extras.getString(NotesDbAdapter.KEY_TITLE);
String body = extras.getString(NotesDbAdapter.KEY_BODY);
mDbHelper.createNote(title, body);
fillData();
break;
case ACTIVITY_EDIT:
Long mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);
if (mRowId != null) {
String editTitle = extras.getString(NotesDbAdapter.KEY_TITLE);
String editBody = extras.getString(NotesDbAdapter.KEY_BODY);
mDbHelper.updateNote(mRowId, editTitle, editBody);
}
fillData();
break;
}</pre>
<ul>
<li>
We are handling both the <code>ACTIVITY_CREATE</code> and
<code>ACTIVITY_EDIT</code> activity results in this method.
</li>
<li>
In the case of a create, we pull the title and body from the extras (retrieved from the
returned Intent) and use them to create a new note.
</li>
<li>
In the case of an edit, we pull the mRowId as well, and use that to update
the note in the database.
</li>
<li>
<code>fillData()</code> at the end ensures everything is up to date .
</li>
</ul>
<h2>Step 7</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>The Art of Layout</h2>
<p>The provided
note_edit.xml layout file is the most sophisticated one in the application we will be building,
but that doesn't mean it is even close to the kind of sophistication you will be likely to want
in real Android applications.</p>
<p>Creating a
good UI is part art and part science, and the rest is work. Mastery of <a
href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring Layout</a> is an essential part of creating
a good looking Android application.</p>
<p>Take a look at the
<a href="{@docRoot}resources/tutorials/views/index.html">Hello Views</a>
for some example layouts and how to use them. The ApiDemos sample project is also a
great resource from which to learn how to create different layouts.</p>
</div>
</div>
<p>Open the file <code>note_edit.xml</code> that has been provided and take a
look at it. This is the UI code for the Note Editor.</p>
<p>This is the most
sophisticated UI we have dealt with yet. The file is given to you to avoid
problems that may sneak in when typing the code. (The XML is very strict
about case sensitivity and structure, mistakes in these are the usual cause
of problems with layout.)</p>
<p>There is a new parameter used
here that we haven't seen before: <code>android:layout_weight</code> (in
this case set to use the value 1 in each case).</p>
<p><code>layout_weight</code> is used in LinearLayouts
to assign "importance" to Views within the layout. All Views have a default
<code>layout_weight</code> of zero, meaning they take up only as much room
on the screen as they need to be displayed. Assigning a value higher than
zero will split up the rest of the available space in the parent View, according
to the value of each View's <code>layout_weight</code> and its ratio to the
overall <code>layout_weight</code> specified in the current layout for this
and other View elements.</p>
<p>To give an example: let's say we have a text label
and two text edit elements in a horizontal row. The label has no
<code>layout_weight</code> specified, so it takes up the minimum space
required to render. If the <code>layout_weight</code> of each of the two
text edit elements is set to 1, the remaining width in the parent layout will
be split equally between them (because we claim they are equally important).
If the first one has a <code>layout_weight</code> of 1
and the second has a <code>layout_weight</code> of 2, then one third of the
remaining space will be given to the first, and two thirds to the
second (because we claim the second one is more important).</p>
<p>This layout also demonstrates how to nest multiple layouts
inside each other to achieve a more complex and pleasant layout. In this
example, a horizontal linear layout is nested inside the vertical one to
allow the title label and text field to be alongside each other,
horizontally.</p>
<h2 style="clear:right;">Step 8</h2>
<p>Create a <code>NoteEdit</code> class that extends
<code>android.app.Activity</code>.</p>
<p>This is the first time we will have
created an Activity without the Android Eclipse plugin doing it for us. When
you do so, the <code>onCreate()</code> method is not automatically
overridden for you. It is hard to imagine an Activity that doesn't override
the <code>onCreate()</code> method, so this should be the first thing you do.</p>
<ol>
<li>Right click on the <code>com.android.demo.notepad2</code> package
in the Package Explorer, and select <strong>New</strong> &gt; <strong>Class</strong> from the popup
menu.</li>
<li>Fill in <code>NoteEdit</code> for the <code>Name:</code> field in the
dialog.</li>
<li>In the <code>Superclass:</code> field, enter
<code>android.app.Activity</code> (you can also just type Activity and hit
Ctrl-Space on Windows and Linux or Cmd-Space on the Mac, to invoke code
assist and find the right package and class).</li>
<li>Click <strong>Finish</strong>.</li>
<li>In the resulting <code>NoteEdit</code> class, right click in the editor
window and select <strong>Source</strong> &gt; <strong>Override/Implement Methods...</strong></li>
<li>Scroll down through the checklist in the dialog until you see
<code>onCreate(Bundle)</code> &mdash; and check the box next to it.</li>
<li>Click <strong>OK</strong>.<p>The method should now appear in your class.</p></li>
</ol>
<h2>Step 9</h2>
<p>Fill in the body of the <code>onCreate()</code> method for <code>NoteEdit</code>.</p>
<p>This will set the title of our new Activity to say "Edit Note" (one
of the strings defined in <code>strings.xml</code>). It will also set the
content view to use our <code>note_edit.xml</code> layout file. We can then
grab handles to the title and body text edit views, and the confirm button,
so that our class can use them to set and get the note title and body,
and attach an event to the confirm button for when it is pressed by the
user.</p>
<p>We can then unbundle the values that were passed in to the Activity
with the extras Bundle attached to the calling Intent. We'll use them to pre-populate
the title and body text edit views so that the user can edit them.
Then we will grab and store the <code>mRowId</code> so we can keep
track of what note the user is editing.</p>
<ol>
<li>
Inside <code>onCreate()</code>, set up the layout:<br>
<pre>setContentView(R.layout.note_edit);</pre>
</li>
<li>
Find the edit and button components we need:
<p>These are found by the
IDs associated to them in the R class, and need to be cast to the right
type of <code>View</code> (<code>EditText</code> for the two text views,
and <code>Button</code> for the confirm button):</p>
<pre>
mTitleText = (EditText) findViewById(R.id.title);
mBodyText = (EditText) findViewById(R.id.body);
Button confirmButton = (Button) findViewById(R.id.confirm);</pre>
<p>Note that <code>mTitleText</code> and <code>mBodyText</code> are member
fields (you need to declare them at the top of the class definition).</p>
</li>
<li>At the top of the class, declare a <code>Long mRowId</code> private field to store
the current <code>mRowId</code> being edited (if any).
</li>
<li>Continuing inside <code>onCreate()</code>,
add code to initialize the <code>title</code>, <code>body</code> and
<code>mRowId</code> from the extras Bundle in
the Intent (if it is present):<br>
<pre>
mRowId = null;
Bundle extras = getIntent().getExtras();
if (extras != null) {
String title = extras.getString(NotesDbAdapter.KEY_TITLE);
String body = extras.getString(NotesDbAdapter.KEY_BODY);
mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);
if (title != null) {
mTitleText.setText(title);
}
if (body != null) {
mBodyText.setText(body);
}
}</pre>
<ul>
<li>
We are pulling the <code>title</code> and
<code>body</code> out of the
<code>extras</code> Bundle that was set from the
Intent invocation.
</li><li>
We also null-protect the text field setting (i.e., we don't want to set
the text fields to null accidentally).</li>
</ul>
</li>
<li>
Create an <code>onClickListener()</code> for the button:
<p>Listeners can be one of the more confusing aspects of UI
implementation, but
what we are trying to achieve in this case is simple. We want an
<code>onClick()</code> method to be called when the user presses the
confirm button, and use that to do some work and return the values
of the edited note to the Intent caller. We do this using something called
an anonymous inner class. This is a bit confusing to look at unless you
have seen them before, but all you really need to take away from this is
that you can refer to this code in the future to see how to create a
listener and attach it to a button. (Listeners are a common idiom
in Java development, particularly for user interfaces.) Here's the empty listener:<br>
<pre>
confirmButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
}
});</pre>
</li>
</ol>
<h2>Step 10</h2>
<p>Fill in the body of the <code>onClick()</code> method of the <code>OnClickListener</code> created in the last step.</p>
<p>This is the code that will be run when the user clicks on the
confirm button. We want this to grab the title and body text from the edit
text fields, and put them into the return Bundle so that they can be passed
back to the Activity that invoked this <code>NoteEdit</code> Activity. If the
operation is an edit rather than a create, we also want to put the
<code>mRowId</code> into the Bundle so that the
<code>Notepadv2</code> class can save the changes back to the correct
note.</p>
<ol>
<li>
Create a <code>Bundle</code> and put the title and body text into it using the
constants defined in Notepadv2 as keys:<br>
<pre>
Bundle bundle = new Bundle();
bundle.putString(NotesDbAdapter.KEY_TITLE, mTitleText.getText().toString());
bundle.putString(NotesDbAdapter.KEY_BODY, mBodyText.getText().toString());
if (mRowId != null) {
bundle.putLong(NotesDbAdapter.KEY_ROWID, mRowId);
}</pre>
</li>
<li>
Set the result information (the Bundle) in a new Intent and finish the Activity:
<pre>
Intent mIntent = new Intent();
mIntent.putExtras(bundle);
setResult(RESULT_OK, mIntent);
finish();</pre>
<ul>
<li>The Intent is simply our data carrier that carries our Bundle
(with the title, body and mRowId).</li>
<li>The <code>setResult()</code> method is used to set the result
code and return Intent to be passed back to the
Intent caller. In this case everything worked, so we return RESULT_OK for the
result code.</li>
<li>The <code>finish()</code> call is used to signal that the Activity
is done (like a return call). Anything set in the Result will then be
returned to the caller, along with execution control.</li>
</ul>
</li>
</ol>
<p>The full <code>onCreate()</code> method (plus supporting class fields) should
now look like this:</p>
<pre>
private EditText mTitleText;
private EditText mBodyText;
private Long mRowId;
&#64;Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.note_edit);
mTitleText = (EditText) findViewById(R.id.title);
mBodyText = (EditText) findViewById(R.id.body);
Button confirmButton = (Button) findViewById(R.id.confirm);
mRowId = null;
Bundle extras = getIntent().getExtras();
if (extras != null) {
String title = extras.getString(NotesDbAdapter.KEY_TITLE);
String body = extras.getString(NotesDbAdapter.KEY_BODY);
mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);
if (title != null) {
mTitleText.setText(title);
}
if (body != null) {
mBodyText.setText(body);
}
}
confirmButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Bundle bundle = new Bundle();
bundle.putString(NotesDbAdapter.KEY_TITLE, mTitleText.getText().toString());
bundle.putString(NotesDbAdapter.KEY_BODY, mBodyText.getText().toString());
if (mRowId != null) {
bundle.putLong(NotesDbAdapter.KEY_ROWID, mRowId);
}
Intent mIntent = new Intent();
mIntent.putExtras(bundle);
setResult(RESULT_OK, mIntent);
finish();
}
});
}</pre>
</li>
</ol>
<h2>Step 11</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>The All-Important Android Manifest File</h2>
<p>The AndroidManifest.xml file is the way in which Android sees your
application. This file defines the category of the application, where
it shows up (or even if it shows up) in the launcher or settings, what
activities, services, and content providers it defines, what intents it can
receive, and more. </p>
<p>For more information, see the reference document
<a href="{@docRoot}guide/topics/manifest/manifest-intro.html">The AndroidManifest.xml
File</a></p>
</div>
</div>
<p>Finally, the new Activity has to be defined in the manifest file:</p>
<p>Before the new Activity can be seen by Android, it needs its own
Activity entry in the <code>AndroidManifest.xml</code> file. This is to let
the system know that it is there and can be called. We could also specify
which IntentFilters the activity implements here, but we are going to skip
this for now and just let Android know that the Activity is
defined.</p>
<p>There is a Manifest editor included in the Eclipse plugin that makes it much easier
to edit the AndroidManifest file, and we will use this. If you prefer to edit the file directly
or are not using the Eclipse plugin, see the box at the end for information on how to do this
without using the new Manifest editor.<p>
<ol>
<li>Double click on the <code>AndroidManifest.xml</code> file in the package explorer to open it.
</li>
<li>Click the <strong>Application</strong> tab at the bottom of the Manifest editor.</li>
<li>Click <strong>Add...</strong> in the Application Nodes section.
<p>If you see a dialog with radiobuttons at the top, select the top radio button:
"Create a new element at the top level, in Application".</p></li>
<li>Make sure "(A) Activity" is selected in the selection pane of the dialog, and click <strong>OK</strong>.</li>
<li>Click on the new "Activity" node, in the Application Nodes section, then
type <code>.NoteEdit</code> into the <em>Name*</em>
field to the right. Press Return/Enter.</li>
</ol>
<p>The Android Manifest editor helps you add more complex entries into the AndroidManifest.xml
file, have a look around at some of the other options available (but be careful not to select
them otherwise they will be added to your Manifest). This editor should help you understand
and alter the AndroidManifest.xml file as you move on to more advanced Android applications.</p>
<p class="note">If you prefer to edit this file directly, simply open the
<code>AndroidManifest.xml</code> file and look at the source (use the
<code>AndroidManifest.xml</code> tab in the eclipse editor to see the source code directly).
Then edit the file as follows:<br>
<code>&lt;activity android:name=".NoteEdit" /&gt;</code><br><br>
This should be placed just below the line that reads:<br>
<code>&lt;/activity&gt;</code> for the <code>.Notepadv2</code> activity.</p>
<h2 style="clear:right;">Step 12</h2>
<p>Now Run it!</p>
<p>You should now be able to add real notes from
the menu, as well as delete an existing one. Notice that in order to delete, you must
first use the directional controls on the device to highlight the note.
Furthermore, selecting a note title from the list should bring up the note
editor to let you edit it. Press confirm when finished to save the changes
back to the database.
<h2>Solution and Next Steps</h2>
<p>You can see the solution to this exercise in <code>Notepadv2Solution</code>
from the zip file to compare with your own.</p>
<p>Now try editing a note, and then hitting the back button on the emulator
instead of the confirm button (the back button is below the menu button). You
will see an error come up. Clearly our application still has some problems.
Worse still, if you did make some changes and hit the back button, when you go
back into the notepad to look at the note you changed, you will find that all
your changes have been lost. In the next exercise we will fix these
problems.</p>
<p>
Once you are ready, move on to <a href="notepad-ex3.html">Tutorial
Exercise 3</a> where you will fix the problems with the back button and lost
edits by introducing a proper life cycle into the NoteEdit Activity.</p>

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page.title=Notepad Exercise 3
parent.title=Notepad Tutorial
parent.link=index.html
@jd:body
<p><em>In this exercise, you will use life-cycle event callbacks to store and
retrieve application state data. This exercise demonstrates:</em></p>
<ul>
<li><em>Life-cycle events and how your application can use them</em></li>
<li><em>Techniques for maintaining application state</em></li>
</ul>
<div style="float:right;white-space:nowrap">
[<a href="notepad-ex1.html">Exercise 1</a>]
[<a href="notepad-ex2.html">Exercise 2</a>]
<span style="color:#BBB;">
[<a href="notepad-ex3.html" style="color:#BBB;">Exercise 3</a>]
</span>
[<a href="notepad-extra-credit.html">Extra Credit</a>]
</div>
<h2>Step 1</h2>
<p>Import <code>Notepadv3</code> into Eclipse. If you see an error about
<code>AndroidManifest.xml,</code> or some problems related to an Android zip
file, right click on the project and select <strong>Android Tools</strong> &gt;
<strong>Fix Project Properties</strong> from the popup menu. The starting point for this exercise is
exactly where we left off at the end of the Notepadv2. </p>
<p>The current application has some problems &mdash; hitting the back button when editing
causes a crash, and anything else that happens during editing will cause the
edits to be lost.</p>
<p>To fix this, we will move most of the functionality for creating and editing
the note into the NoteEdit class, and introduce a full life cycle for editing
notes.</p>
<ol>
<li>Remove the code in <code>NoteEdit</code> that parses the title and body
from the extras Bundle.
<p>Instead, we are going to use the <code>DBHelper</code> class
to access the notes from the database directly. All we need passed into the
NoteEdit Activity is a <code>mRowId</code> (but only if we are editing, if creating we pass
nothing). Remove these lines:</p>
<pre>
String title = extras.getString(NotesDbAdapter.KEY_TITLE);
String body = extras.getString(NotesDbAdapter.KEY_BODY);</pre>
</li>
<li>We will also get rid of the properties that were being passed in
the <code>extras</code> Bundle, which we were using to set the title
and body text edit values in the UI. So delete:
<pre>
if (title != null) {
mTitleText.setText(title);
}
if (body != null) {
mBodyText.setText(body);
}</pre>
</li>
</ol>
<h2>Step 2</h2>
<p>Create a class field for a <code>NotesDbAdapter</code> at the top of the NoteEdit class:</p>
<pre>&nbsp;&nbsp;&nbsp; private NotesDbAdapter mDbHelper;</pre>
<p>Also add an instance of <code>NotesDbAdapter</code> in the
<code>onCreate()</code> method (right below the <code>super.onCreate()</code> call):</p>
<pre>
&nbsp;&nbsp;&nbsp; mDbHelper = new NotesDbAdapter(this);<br>
&nbsp;&nbsp;&nbsp; mDbHelper.open();</pre>
<h2>Step 3</h2>
<p>In <code>NoteEdit</code>, we need to check the <var>savedInstanceState</var> for the
<code>mRowId</code>, in case the note
editing contains a saved state in the Bundle, which we should recover (this would happen
if our Activity lost focus and then restarted).</p>
<ol>
<li>
Replace the code that currently initializes the <code>mRowId</code>:<br>
<pre>
mRowId = null;
Bundle extras = getIntent().getExtras();
if (extras != null) {
mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);
}
</pre>
with this:
<pre>
mRowId = (savedInstanceState == null) ? null :
(Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID);
if (mRowId == null) {
Bundle extras = getIntent().getExtras();
mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID)
: null;
}
</pre>
</li>
<li>
Note the null check for <code>savedInstanceState</code>, and we still need to load up
<code>mRowId</code> from the <code>extras</code> Bundle if it is not
provided by the <code>savedInstanceState</code>. This is a ternary operator shorthand
to safely either use the value or null if it is not present.
</li>
<li>
Note the use of <code>Bundle.getSerializable()</code> instead of
<code>Bundle.getLong()</code>. The latter encoding returns a <code>long</code> primitive and
so can not be used to represent the case when <code>mRowId</code> is <code>null</code>.
</li>
</ol>
<h2>Step 4</h2>
<p>Next, we need to populate the fields based on the <code>mRowId</code> if we
have it:</p>
<pre>populateFields();</pre>
<p>This goes before the <code>confirmButton.setOnClickListener()</code> line.
We'll define this method in a moment.</p>
<h2>Step 5</h2>
<p>Get rid of the Bundle creation and Bundle value settings from the
<code>onClick()</code> handler method. The Activity no longer needs to
return any extra information to the caller. And because we no longer have
an Intent to return, we'll use the shorter version
of <code>setResult()</code>:</p>
<pre>
public void onClick(View view) {
setResult(RESULT_OK);
finish();
}</pre>
<p>We will take care of storing the updates or new notes in the database
ourselves, using the life-cycle methods.</p>
<p>The whole <code>onCreate()</code> method should now look like this:</p>
<pre>
super.onCreate(savedInstanceState);
mDbHelper = new NotesDbAdapter(this);
mDbHelper.open();
setContentView(R.layout.note_edit);
mTitleText = (EditText) findViewById(R.id.title);
mBodyText = (EditText) findViewById(R.id.body);
Button confirmButton = (Button) findViewById(R.id.confirm);
mRowId = (savedInstanceState == null) ? null :
(Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID);
if (mRowId == null) {
Bundle extras = getIntent().getExtras();
mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID)
: null;
}
populateFields();
confirmButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
setResult(RESULT_OK);
finish();
}
});</pre>
<h2>Step 6</h2>
<p>Define the <code>populateFields()</code> method.</p>
<pre>
private void populateFields() {
if (mRowId != null) {
Cursor note = mDbHelper.fetchNote(mRowId);
startManagingCursor(note);
mTitleText.setText(note.getString(
note.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));
mBodyText.setText(note.getString(
note.getColumnIndexOrThrow(NotesDbAdapter.KEY_BODY)));
}
}</pre>
<p>This method uses the <code>NotesDbAdapter.fetchNote()</code> method to find the right note to
edit, then it calls <code>startManagingCursor()</code> from the <code>Activity</code> class, which
is an Android convenience method provided to take care of the Cursor life-cycle. This will release
and re-create resources as dictated by the Activity life-cycle, so we don't need to worry about
doing that ourselves. After that, we just look up the title and body values from the Cursor
and populate the View elements with them.</p>
<h2>Step 7</h2>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Why handling life-cycle events is important</h2>
<p>If you are used to always having control in your applications, you
might not understand why all this life-cycle work is necessary. The reason
is that in Android, you are not in control of your Activity, the
operating system is!</p>
<p>As we have already seen, the Android model is based around activities
calling each other. When one Activity calls another, the current Activity
is paused at the very least, and may be killed altogether if the
system starts to run low on resources. If this happens, your Activity will
have to store enough state to come back up later, preferably in the same
state it was in when it was killed.</p>
<p>
Android has a <a href="{@docRoot}guide/topics/fundamentals.html#lcycles">well-defined life
cycle</a>.
Lifecycle events can happen even if you are not handing off control to
another Activity explicitly. For example, perhaps a call comes in to the
handset. If this happens, and your Activity is running, it will be swapped
out while the call Activity takes over.</p>
</div>
</div>
<p>Still in the <code>NoteEdit</code> class, we now override the methods
<code>onSaveInstanceState()</code>, <code>onPause()</code> and
<code>onResume()</code>. These are our life-cycle methods
(along with <code>onCreate()</code> which we already have).</p>
<p><code>onSaveInstanceState()</code> is called by Android if the
Activity is being stopped and <strong>may be killed before it is
resumed!</strong> This means it should store any state necessary to
re-initialize to the same condition when the Activity is restarted. It is
the counterpart to the <code>onCreate()</code> method, and in fact the
<code>savedInstanceState</code> Bundle passed in to <code>onCreate()</code> is the same
Bundle that you construct as <code>outState</code> in the
<code>onSaveInstanceState()</code> method.</p>
<p><code>onPause()</code> and <code>onResume()</code> are also
complimentary methods. <code>onPause()</code> is always called when the
Activity ends, even if we instigated that (with a <code>finish()</code> call for example).
We will use this to save the current note back to the database. Good
practice is to release any resources that can be released during an
<code>onPause()</code> as well, to take up less resources when in the
passive state. <code>onResume()</code> will call our <code>populateFields()</code> method
to read the note out of the database again and populate the fields.</p>
<p>So, add some space after the <code>populateFields()</code> method
and add the following life-cycle methods:</p>
<ol type="a">
<li><code>
onSaveInstanceState()</code>:
<pre>
&#64;Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
saveState();
outState.putSerializable(NotesDbAdapter.KEY_ROWID, mRowId);
}</pre>
<p>We'll define <code>saveState()</code> next.</p>
</li>
<li><code>
onPause()</code>:
<pre>
&#64;Override
protected void onPause() {
super.onPause();
saveState();
}</pre>
</li>
<li><code>
onResume()</code>:
<pre>
&#64;Override
protected void onResume() {
super.onResume();
populateFields();
}</pre>
</li>
</ol>
<p>Note that <code>saveState()</code> must be called in both <code>onSaveInstanceState()</code>
and <code>onPause()</code> to ensure that the data is saved. This is because there is no
guarantee that <code>onSaveInstanceState()</code> will be called and because when it <em>is</em>
called, it is called before <code>onPause()</code>.</p>
<h2 style="clear:right;">Step 8</h2>
<p>Define the <code>saveState()</code> method to put the data out to the
database.</p>
<pre>
private void saveState() {
String title = mTitleText.getText().toString();
String body = mBodyText.getText().toString();
if (mRowId == null) {
long id = mDbHelper.createNote(title, body);
if (id > 0) {
mRowId = id;
}
} else {
mDbHelper.updateNote(mRowId, title, body);
}
}</pre>
<p>Note that we capture the return value from <code>createNote()</code> and if a valid row ID is
returned, we store it in the <code>mRowId</code> field so that we can update the note in future
rather than create a new one (which otherwise might happen if the life-cycle events are
triggered).</p>
<h2 style="clear:right;">Step 9</h2>
<p>Now pull out the previous handling code from the
<code>onActivityResult()</code> method in the <code>Notepadv3</code>
class.</p>
<p>All of the note retrieval and updating now happens within the
<code>NoteEdit</code> life cycle, so all the <code>onActivityResult()</code>
method needs to do is update its view of the data, no other work is
necessary. The resulting method should look like this:</p>
<pre>
&#64;Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
super.onActivityResult(requestCode, resultCode, intent);
fillData();
}</pre>
<p>Because the other class now does the work, all this has to do is refresh
the data.</p>
<h2>Step 10</h2>
<p>Also remove the lines which set the title and body from the
<code>onListItemClick()</code> method (again they are no longer needed,
only the <code>mRowId</code> is):</p>
<pre>
Cursor c = mNotesCursor;
c.moveToPosition(position);</pre>
<br>
and also remove:
<br>
<pre>
i.putExtra(NotesDbAdapter.KEY_TITLE, c.getString(
c.getColumnIndex(NotesDbAdapter.KEY_TITLE)));
i.putExtra(NotesDbAdapter.KEY_BODY, c.getString(
c.getColumnIndex(NotesDbAdapter.KEY_BODY)));</pre>
<br>
so that all that should be left in that method is:
<br>
<pre>
super.onListItemClick(l, v, position, id);
Intent i = new Intent(this, NoteEdit.class);
i.putExtra(NotesDbAdapter.KEY_ROWID, id);
startActivityForResult(i, ACTIVITY_EDIT);</pre>
<p>You can also now remove the mNotesCursor field from the class, and set it back to using
a local variable in the <code>fillData()</code> method:
<br><pre>
Cursor notesCursor = mDbHelper.fetchAllNotes();</pre></p>
<p>Note that the <code>m</code> in <code>mNotesCursor</code> denotes a member field, so when we
make <code>notesCursor</code> a local variable, we drop the <code>m</code>. Remember to rename the
other occurrences of <code>mNotesCursor</code> in your <code>fillData()</code> method.
</ol>
<p>
Run it! (use <em>Run As -&gt; Android Application</em> on the project right
click menu again)</p>
<h2>Solution and Next Steps</h2>
<p>You can see the solution to this exercise in <code>Notepadv3Solution</code>
from
the zip file to compare with your own.</p>
<p>
When you are ready, move on to the <a href="notepad-extra-credit.html">Tutorial
Extra Credit</a> exercise, where you can use the Eclipse debugger to
examine the life-cycle events as they happen.</p>

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page.title=Notepad Extra Credit
parent.title=Notepad Tutorial
parent.link=index.html
@jd:body
<p><em>In this exercise, you will use the debugger to look at the work you did
in Exercise 3. This exercise demonstrates:</em></p>
<ul>
<li><em>How to set breakpoints to observe execution</em> </li>
<li><em>How to run your application in debug mode</code></em></li>
</ul>
<div style="float:right;white-space:nowrap">
[<a href="notepad-ex1.html">Exercise 1</a>]
[<a href="notepad-ex2.html">Exercise 2</a>]
[<a href="notepad-ex3.html">Exercise 3</a>]
<span style="color:#BBB;">
[<a href="notepad-extra-credit.html" style="color:#BBB;">Extra Credit</a>]
</span>
</div>
<h2>Step 1</h2>
<p>Using the working <code>Notepadv3</code>, put breakpoints in the code at the
beginning of the <code>onCreate()</code>, <code>onPause()</code>,
<code>onSaveInstanceState()</code> and <code>onResume()</code> methods in the
<code>NoteEdit</code> class (if you are not familiar with Eclipse, just
right click in the narrow grey border on the left of the edit window at the
line you want a breakpoint, and select <em>Toggle Breakpoint</em>, you
should see a blue dot appear).</p>
<h2>Step 2</h2>
<p>Now start the notepad demo in debug mode:</p>
<ol type="a">
<li>
Right click on the <code>Notepadv3</code> project and from the Debug menu
select <em>Debug As -&gt; Android Application.</em></li>
<li>
The Android emulator should say <em>"waiting for debugger to connect"</em>
briefly and then run the application.</li>
<li>
If it gets stuck on the waiting... screen, quit the emulator and Eclipse,
from the command line do an <code>adb kill-server</code>, and then restart
Eclipse and try again.</li></ol>
<h2>Step 3</h2>
<p>When you edit or create a new note you should see the breakpoints getting
hit and the execution stopping.</p>
<h2>Step 4</h2>
<p>Hit the Resume button to let execution continue (yellow rectangle with a
green triangle to its right in the Eclipse toolbars near the top).</p>
<h2>Step 5</h2>
<p>Experiment a bit with the confirm and back buttons, and try pressing Home and
making other mode changes. Watch what life-cycle events are generated and
when.</p>
<p>The Android Eclipse plugin not only offers excellent debugging support for
your application development, but also superb profiling support. You can also
try using <a href="{@docRoot}guide/developing/tools/traceview.html">Traceview</a> to profile your application. If your application is running too slow, this can help you
find the bottlenecks and fix them.</p>

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page.title=Notepad Tutorial
@jd:body
<p>The tutorial in this section gives you a &quot;hands-on&quot; introduction
to the Android framework and the tools you use to build applications on it.
Starting from a preconfigured project file, it guides you through the process of
developing a simple notepad application and provides concrete examples of how to
set up the project, develop the application logic and user interface, and then
compile and run the application. </p>
<p>The tutorial presents the notepad application development as a set of
exercises (see below), each consisting of several steps. You can follow along
with the steps in each exercise and gradually build up and refine your
application. The exercises explain each step in detail and provide all the
sample code you need to complete the application. </p>
<p>When you are finished with the tutorial, you will have created a functioning
Android application and learned in depth about many of the most important
concepts in Android development. If you want to add more complex features to
your application, you can examine the code in an alternative implementation
of a notepad application, in the
<a href="{@docRoot}samples/NotePad/index.html">Sample Code</a> documentation. </p>
<a name="who"></a>
<h2>Who Should Use this Tutorial</h2>
<p>This tutorial is designed for experienced developers, especially those with
knowledge of the Java programming language. If you haven't written Java
applications before, you can still use the tutorial, but you might need to work
at a slower pace. </p>
<p>The tutorial assumes that you have some familiarity with the basic Android
application concepts and terminology. If you aren't yet familiar with those, you
should read <a href="{@docRoot}intro/anatomy.html">Overview of an Android
Application</a> before continuing. </p>
<p>Also note that this tutorial uses
the Eclipse development environment, with the Android plugin installed. If you
are not using Eclipse, you can follow the exercises and build the application,
but you will need to determine how to accomplish the Eclipse-specific
steps in your environment. </p>
<a name="preparing"></a>
<h2>Preparing for the Exercises</h2>
<p>This tutorial builds on the information provided in the <a
href="{@docRoot}intro/installing.html">Installing the SDK</a> and <a
href="{@docRoot}intro/hello-android.html">Hello Android</a>
documents, which explain in detail how to set up your development environment
for building Android applications. Before you start this tutorial, you should
read both these documents, have the SDK installed, and your work environment set up.</p>
<p>To prepare for this lesson:</p>
<ol>
<li>Download the <a href="codelab/NotepadCodeLab.zip">project
exercises archive (.zip)</a></li>
<li>Unpack the archive file to a suitable location on your machine</li>
<li>Open the <code>NotepadCodeLab</code> folder</li>
</ol>
<p>Inside the <code>NotepadCodeLab</code> folder, you should see six project
files: <code>Notepadv1</code>,
<code>Notepadv2</code>, <code>Notepadv3</code>,
<code>Notepadv1Solution</code>, <code>Notepadv2Solution</code>
and <code>Notepadv3Solution</code>. The <code>Notepadv#</code> projects are
the starting points for each of the exercises, while the
<code>Notepadv#Solution</code> projects are the exercise
solutions. If you are having trouble with a particular exercise, you
can compare your current work against the exercise solution.</p>
<a name="exercises"></a>
<h2> Exercises</h2>
<p>The table below lists the tutorial exercises and describes the development
areas that each covers. Each exercise assumes that you have completed any
previous exercises.</p>
<table border="0" style="padding:4px;spacing:2px;" summary="This
table lists the
tutorial examples and describes what each covers. ">
<tr>
<th width="120"><a href="{@docRoot}intro/tutorial-ex1.html">Exercise
1</a></th>
<td>Start here. Construct a simple notes list that lets the user add new notes but not
edit them. Demonstrates the basics of <code>ListActivity</code> and creating
and handling
menu options. Uses a SQLite database to store the notes.</td>
</tr>
<tr>
<th><a href="{@docRoot}intro/tutorial-ex2.html">Exercise 2</a></th>
<td>Add a second Activity to the
application. Demonstrates constructing a
new Activity, adding it to the Android manifest, passing data between the
activities, and using more advanced screen layout. Also shows how to
invoke another Activity to return a result, using
<code>startActivityForResult()</code>.</td>
</tr>
<tr>
<th><a href="{@docRoot}intro/tutorial-ex3.html">Exercise 3</a></th>
<td>Add handling of life-cycle events to
the application, to let it
maintain application state across the life cycle. </td>
</tr>
<tr>
<th><a href="{@docRoot}intro/tutorial-extra-credit.html">Extra
Credit</a></th>
<td>Demonstrates how to use the Eclipse
debugger and how you can use it to
view life-cycle events as they are generated. This section is optional but
highly recommended.</td>
</tr>
</table>
<a name="other"></a>
<h2>Other Resources and Further Learning</h2>
<ul>
<li>For a lighter but broader introduction to concepts not covered in the
tutorial,
take a look at <a href="{@docRoot}kb/commontasks.html">Common Android Tasks</a>.</li>
<li>The Android SDK includes a variety of fully functioning sample applications
that make excellent opportunities for further learning. You can find the sample
applications in the <code>samples/</code> directory of your downloaded SDK.</li>
<li>This tutorial draws from the full Notepad application included in the
<code>samples/</code> directory of the SDK, though it does not match it exactly.
When you are done with the tutorial,
it is highly recommended that you take a closer look at this version of the Notepad
application,
as it demonstrates a variety of interesting additions for your application,
such as:</li>
<ul>
<li>Setting up a custom striped list for the list of notes.</li>
<li>Creating a custom text edit view that overrides the <code>draw()</code>
method to
make it look like a lined notepad.</li>
<li>Implementing a full <code>ContentProvider</code> for notes.</li>
<li>Reverting and discarding edits instead of just automatically saving
them.</li>
</ul>
</ul>