M7350/base/docs/html/guide/topics/appwidgets/index.jd

page.title=App Widgets
@jd:body

<div id="qv-wrapper">
  <div id="qv">
    <h2>Quickview</h2>
    <ul>
      <li>App Widgets provide users access to some of your application features
directly from the Home screen (without the need to launch an activity)</li>
      <li>App Widgets are backed by a special kind of broadcast receiver that handles the App
Widget lifecycle</li>
    </ul>
    
    <h2>In this document</h2>
    <ol>
      <li><a href="#Basics">The Basics</a></li>
      <li><a href="#Manifest">Declaring an App Widget in the Manifest</a></li>
      <li><a href="#MetaData">Adding the AppWidgetProviderInfo Metadata</a></li>
      <li><a href="#CreatingLayout">Creating the App Widget Layout</a></li>
      <li><a href="#AppWidgetProvider">Using the AppWidgetProvider Class</a>
        <ol>
          <li><a href="#ProviderBroadcasts">Receiving App Widget broadcast Intents</a></li>
        </ol>
      </li>
      <li><a href="#Configuring">Creating an App Widget Configuration Activity</a>
        <ol>
          <li><a href="#UpdatingFromTheConfiguration">Updating the App Widget from 
            the configuration Activity</a></li>
        </ol>
      </li>
    </ol>

    <h2>Key classes</h2>
    <ol>
      <li>{@link android.appwidget.AppWidgetProvider}</li>
      <li>{@link android.appwidget.AppWidgetProviderInfo}</li>
      <li>{@link android.appwidget.AppWidgetManager}</li>
    </ol>
    
    <h2>See also</h2>
    <ol>
      <li><a href="{@docRoot}guide/practices/ui_guidelines/widget_design.html">App Widget Design 
        Guidelines</a></li>
      <li><a href="http://android-developers.blogspot.com/2009/04/introducing-home-screen-widgets-and.html">Introducing
        home screen widgets and the AppWidget framework &raquo;</a></li>
    </ol>
  </div>
</div>


<p>App Widgets are miniature application views that can be embedded in other applications
(such as the Home screen) and receive periodic updates. These views are referred 
to as Widgets in the user interface,
and you can publish one with an App Widget provider. An application component that is 
able to hold other App Widgets is called an App Widget host. The screenshot below shows
the Music App Widget.</p>

<img src="{@docRoot}images/appwidget.png" alt="" />

<p>This document describes how to publish an App Widget using an App Widget provider.</p>


<h2 id="Basics">The Basics</h2>

<p>To create an App Widget, you need the following:</p>

<dl>
  <dt>{@link android.appwidget.AppWidgetProviderInfo} object</dt>
  <dd>Describes the metadata for an App Widget, such as the App Widget's layout, update frequency,
    and the AppWidgetProvider class. This should be defined in XML.</dd>
  <dt>{@link android.appwidget.AppWidgetProvider} class implementation</dt>
  <dd>Defines the basic methods that allow you to programmatically interface with the App Widget,
    based on broadcast events. Through it, you will receive broadcasts when the App Widget is updated, 
    enabled, disabled and deleted.</dd>
  <dt>View layout</dt>
  <dd>Defines the initial layout for the App Widget, defined in XML.</dd>
</dl>

<p>Additionally, you can implement an App Widget configuration Activity. This is an optional 
{@link android.app.Activity} that launches when the user adds your App Widget and allows him or her
to modify App Widget settings at create-time.</p>

<p>The following sections describe how to setup each of these components.</p>


<h2 id="Manifest">Declaring an App Widget in the Manifest</h2>

<p>First, declare the {@link android.appwidget.AppWidgetProvider} class in your application's
<code>AndroidManifest.xml</code> file. For example:</p>

<pre>
&lt;receiver android:name="ExampleAppWidgetProvider" >
    &lt;intent-filter>
        &lt;action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
    &lt;/intent-filter>
    &lt;meta-data android:name="android.appwidget.provider"
               android:resource="@xml/example_appwidget_info" />
&lt;/receiver>
</pre>

<p>The <code>&lt;receiver&gt;</code> element requires the <code>android:name</code> 
attribute, which specifies the {@link android.appwidget.AppWidgetProvider} used
by the App Widget.</p>

<p>The <code>&lt;intent-filter&gt;</code> element must include an <code>&lt;action></code>
element with the <code>android:name</code> attribute. This attribute specifies
that the {@link android.appwidget.AppWidgetProvider} accepts the {@link
android.appwidget.AppWidgetManager#ACTION_APPWIDGET_UPDATE ACTION_APPWIDGET_UPDATE} broadcast.
This is the only broadcast that you must explicitly declare. The {@link android.appwidget.AppWidgetManager}
automatically sends all other App Widget broadcasts to the AppWidgetProvider as necessary.</p>

<p>The <code>&lt;meta-data&gt;</code> element specifies the
{@link android.appwidget.AppWidgetProviderInfo} resource and requires the 
following attributes:</p>
<ul>
  <li><code>android:name</code> - Specifies the metadata name. Use <code>android.appwidget.provider</code>
    to identify the data as the {@link android.appwidget.AppWidgetProviderInfo} descriptor.</li>
  <li><code>android:resource</code> - Specifies the {@link android.appwidget.AppWidgetProviderInfo} 
    resource location.</li>
</ul>


<h2 id="MetaData">Adding the AppWidgetProviderInfo Metadata</h2>

<p>The {@link android.appwidget.AppWidgetProviderInfo} defines the essential 
qualities of an App Widget, such as its minimum layout dimensions, its initial layout resource,
how often to update the App Widget, and (optionally) a configuration Activity to launch at create-time.
Define the AppWidgetProviderInfo object in an XML resource using a single
<code>&lt;appwidget-provider></code> element and save it in the project's <code>res/xml/</code> 
folder.</p>

<p>For example:</p>

<pre>
&lt;appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:minWidth="294dp"
    android:minHeight="72dp"
    android:updatePeriodMillis="86400000"
    android:initialLayout="@layout/example_appwidget"
    android:configure="com.example.android.ExampleAppWidgetConfigure" >
&lt;/appwidget-provider>
</pre>

<p>Here's a summary of the <code>&lt;appwidget-provider></code> attributes:</p>
<ul>
  <li>The values for the <code>minWidth</code> and <code>minHeight</code> attributes specify the minimum
    area required by the App Widget's layout.
    <p>The default Home screen positions App Widgets in its window based on a grid of
    cells that have a defined height and width. If the values for an App Widget's minimum width 
    or height don't match the dimensions of the cells,
    then the App Widget dimensions round <em>up</em> to the nearest cell size.
    (See the <a href="{@docRoot}guide/practices/ui_guidelines/widget_design.html">App Widget Design 
    Guidelines</a> for more information on the Home screen cell sizes.)</p>
    <p>Because the Home screen's layout orientation (and thus, the cell sizes) can change,
    as a rule of thumb, you should assume the worst-case cell size of 74 pixels for the height
    <em>and</em> width of a cell. However, you must subtract 2 from the final dimension to account
    for any integer rounding errors that occur in the pixel count. To find your minimum width
    and height in density-independent pixels (dp), use this formula:<br/>
      <code>(number of cells * 74) - 2</code><br/>
    Following this formula, you should use 72 dp for a height of one cell, 294 dp and for a width of four cells.</p>
  </li>
  <li>The <code>updatePeriodMillis</code> attribute defines how often the App Widget framework should
    request an update from the {@link android.appwidget.AppWidgetProvider} by calling the
    {@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
    onUpdate()} method. The actual update is not guaranteed to occur exactly on time with this value
    and we suggest updating as infrequently as possible&mdash;perhaps no more than once an hour to 
    conserve the battery. You might also allow the user to adjust the frequency in a 
    configuration&mdash;some people might want a stock ticker to update every 15 minutes, or maybe 
    only four times a day. 
    	<p class="note"><strong>Note:</strong> If the device is asleep when it is time for an update 
    	(as defined by <code>updatePeriodMillis</code>), then the device will wake up in order 
    	to perform the update. If you don't update more than once per hour, this probably won't 
    	cause significant problems for the battery life. If, however, you need to update more 
    	frequently and/or you do not need to update while the device is asleep, then you can instead 
    	perform updates based on an alarm that will not wake the device. To do so, set an alarm with 
    	an Intent that your AppWidgetProvider receives, using the	{@link android.app.AlarmManager}. 
    	Set the alarm type to either {@link android.app.AlarmManager#ELAPSED_REALTIME} or 
    	{@link android.app.AlarmManager#RTC}, which will only
    	deliver the alarm when the device is awake. Then set <code>updatePeriodMillis</code> to 
    	zero (<code>"0"</code>).</p>
  </li>
  <li>The <code>initialLayout</code> attribute points to the layout resource that defines the
    App Widget layout.</li>
  <li>The <code>configure</code> attribute defines the {@link android.app.Activity} to launch when
    the user adds the App Widget, in order for him or her to configure App Widget properties. This is optional
    (read <a href="#Configuring">Creating an App Widget Configuration Activity</a> below).</li>
</ul>

<p>See the {@link android.appwidget.AppWidgetProviderInfo} class for more information on the
attributes accepted by the <code>&lt;appwidget-provider></code> element.</p>


<h2 id="CreatingLayout">Creating the App Widget Layout</h2>

<p>You must define an initial layout for your App Widget in XML and save it in the project's
<code>res/layout/</code> directory. You can design your App Widget using the View objects listed
below, but before you begin designing your App Widget, please read and understand the
<a href="{@docRoot}guide/practices/ui_guidelines/widget_design.html">App Widget Design 
Guidelines</a>.</p>

<p>Creating the App Widget layout is simple if you're
familiar with <a href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring Layout in XML</a>.
However, you must be aware that App Widget layouts are based on {@link android.widget.RemoteViews},
which do not support every kind of layout or view widget.</p>

<p>A RemoteViews object (and, consequently, an App Widget) can support the 
following layout classes:</p>

<ul class="nolist">
  <li>{@link android.widget.FrameLayout}</li>
  <li>{@link android.widget.LinearLayout}</li>
  <li>{@link android.widget.RelativeLayout}</li>
</ul>

<p>And the following widget classes:</p>
<ul class="nolist">
  <li>{@link android.widget.AnalogClock}</li>
  <li>{@link android.widget.Button}</li>
  <li>{@link android.widget.Chronometer}</li>
  <li>{@link android.widget.ImageButton}</li>
  <li>{@link android.widget.ImageView}</li>
  <li>{@link android.widget.ProgressBar}</li>
  <li>{@link android.widget.TextView}</li>
</ul>

<p>Descendants of these classes are not supported.</p>


<h2 id="AppWidgetProvider">Using the AppWidgetProvider Class</h2>

<div class="sidebox-wrapper">
<div class="sidebox">
    <p>You must declare your AppWidgetProvider class implementation as a broadcast receiver 
    using the <code>&lt;receiver></code> element in the AndroidManifest (see
    <a href="#Manifest">Declaring an App Widget in the Manifest</a> above).</p>
  </div>
</div>

<p>The {@link android.appwidget.AppWidgetProvider} class extends BroadcastReceiver as a convenience
class to handle the App Widget broadcasts. The AppWidgetProvider receives only the event broadcasts that
are relevant to the App Widget, such as when the App Widget is updated, deleted, enabled, and disabled.
When these broadcast events occur, the AppWidgetProvider receives the following method calls:</p>

<dl>
  <dt>{@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])}</dt>
    <dd>This is called to update the App Widget at intervals defined by the <code>updatePeriodMillis</code>
    attribute in the AppWidgetProviderInfo (see <a href="#MetaData">Adding the 
    AppWidgetProviderInfo Metadata</a> above). This method is also called
    when the user adds the App Widget, so it should perform the essential setup,
    such as define event handlers for Views and start a temporary
    {@link android.app.Service}, if necessary. However, if you have declared a configuration
    Activity, <strong>this method is not called</strong> when the user adds the App Widget,
    but is called for the subsequent updates. It is the responsibility of the 
    configuration Activity to perform the first update when configuration is done.
    (See <a href="#Configuring">Creating an App Widget Configuration Activity</a> below.)</dd> 
  <dt>{@link android.appwidget.AppWidgetProvider#onDeleted(Context,int[])}</dt>
    <dd>This is called every time an App Widget is deleted from the App Widget host.</dd>
  <dt>{@link android.appwidget.AppWidgetProvider#onEnabled(Context)}</dt>
    <dd>This is called when an instance the App Widget is created for the first time. For example, if the user 
    adds two instances of your App Widget, this is only called the first time.
    If you need to open a new database or perform other setup that only needs to occur once 
    for all App Widget instances, then this is a good place to do it.</dd> 
  <dt>{@link android.appwidget.AppWidgetProvider#onDisabled(Context)}</dt>
    <dd>This is called when the last instance of your App Widget is deleted from the App Widget host. 
    This is where you should clean up any work done in 
    {@link android.appwidget.AppWidgetProvider#onEnabled(Context)}, 
    such as delete a temporary database.</dd> 
  <dt>{@link android.appwidget.AppWidgetProvider#onReceive(Context,Intent)}</dt>
    <dd>This is called for every broadcast and before each of the above callback methods.
    You normally don't need to implement this method because the default AppWidgetProvider 
    implementation filters all App Widget broadcasts and calls the above 
    methods as appropriate.</dd> 
</dl>

<p class="warning"><strong>Note:</strong> In Android 1.5, there is a known issue in which the
<code>onDeleted()</code> method will not be called when it should be. To work around this issue, 
you can implement {@link android.appwidget.AppWidgetProvider#onReceive(Context,Intent)
onReceive()} as described in this 
<a href="http://groups.google.com/group/android-developers/msg/e405ca19df2170e2">Group post</a>
to receive the <code>onDeleted()</code> callback.
</p>

<p>The most important AppWidgetProvider callback is 
{@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
onUpdated()} because it is called when each App Widget is added to a host (unless you use
a configuration Activity). If your App Widget accepts any
user interaction events, then you need to register the event handlers in this callback.
If your App Widget doesn't create temporary
files or databases, or perform other work that requires clean-up, then
{@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
onUpdated()} may be the only callback method you need to define. For example, if you want an App Widget
with a button that launches an Activity when clicked, you could use the following
implementation of AppWidgetProvider:</p>

<pre>
public class ExampleAppWidgetProvider extends AppWidgetProvider {

    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        final int N = appWidgetIds.length;

        // Perform this loop procedure for each App Widget that belongs to this provider
        for (int i=0; i&lt;N; i++) {
            int appWidgetId = appWidgetIds[i];

            // Create an Intent to launch ExampleActivity
            Intent intent = new Intent(context, ExampleActivity.class);
            PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, 0);

            // Get the layout for the App Widget and attach an on-click listener to the button
            RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.appwidget_provider_layout);
            views.setOnClickPendingIntent(R.id.button, pendingIntent);

            // Tell the AppWidgetManager to perform an update on the current App Widget
            appWidgetManager.updateAppWidget(appWidgetId, views);
        }
    }
}
</pre>

<p>This AppWidgetProvider defines only the 
{@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
onUpdated()} method for the purpose
of defining a {@link android.app.PendingIntent} that launches an {@link android.app.Activity}
and attaching it to the App Widget's button
with {@link android.widget.RemoteViews#setOnClickPendingIntent(int,PendingIntent)}.
Notice that it includes a loop that iterates through each entry in <code>appWidgetIds</code>, which
is an array of IDs that identify each App Widget created by this provider.
In this way, if the user creates more than one instance of the App Widget, then they are
all updated simultaneously. However, only one <code>updatePeriodMillis</code> schedule will be 
managed for all instances of the App Widget. For example, if the update schedule is defined 
to be every two hours, and a second instance 
of the App Widget is added one hour after the first one, then they will both be updated 
on the period defined by the first one and the second update period will be ignored 
(they'll both be updated every two hours, not every hour).</p>

<p class="note"><strong>Note:</strong> Because the AppWidgetProvider is a BroadcastReceiver,
your process is not guaranteed to keep running after the callback methods return (see
<a href="{@docRoot}guide/topics/fundamentals.html#broadlife">Application Fundamentals &gt;
Broadcast Receiver Lifecycle</a> for more information). If your App Widget setup process can take several
seconds (perhaps while performing web requests) and you require that your process continues, 
consider starting a {@link android.app.Service} 
in the {@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
onUpdated()} method. From within the Service, you can perform your own updates to the App Widget
without worrying about the AppWidgetProvider closing down due to an 
<a href="{@docRoot}guide/practices/design/responsiveness.html">Application Not Responding</a> 
(ANR) error. See the
<a href="http://code.google.com/p/wiktionary-android/source/browse/trunk/Wiktionary/src/com/example/android/wiktionary/WordWidget.java">Wiktionary
sample's AppWidgetProvider</a> for an example of an App Widget running a {@link android.app.Service}.</p>

<p>Also see the <a 
href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/appwidget/ExampleAppWidgetProvider.html">
ExampleAppWidgetProvider.java</a> sample class.</p>


<h3 id="ProviderBroadcasts">Receiving App Widget broadcast Intents</h3>

<p>{@link android.appwidget.AppWidgetProvider} is just a convenience class.  If you would like
to receive the App Widget broadcasts directly, you can implement your own 
{@link android.content.BroadcastReceiver} or override the 
{@link android.appwidget.AppWidgetProvider#onReceive(Context,Intent)} callback. 
The four Intents you need to care about are:</p>
<ul>
  <li>{@link android.appwidget.AppWidgetManager#ACTION_APPWIDGET_UPDATE}</li>
  <li>{@link android.appwidget.AppWidgetManager#ACTION_APPWIDGET_DELETED}</li>
  <li>{@link android.appwidget.AppWidgetManager#ACTION_APPWIDGET_ENABLED}</li>
  <li>{@link android.appwidget.AppWidgetManager#ACTION_APPWIDGET_DISABLED}</li>
</ul>



<h2 id="Configuring">Creating an App Widget Configuration Activity</h2>

<p>If you would like the user to configure settings when he or she adds a new App Widget,
you can create an App Widget configuration Activity. This {@link android.app.Activity} 
will be automatically launched by the App Widget host and allows the user to configure
available settings for the App Widget at create-time, such as the App Widget color, size, 
update period or other functionality settings.</p>

<p>The configuration Activity should be declared as a normal Activity in the Android manifest file.
However, it will be launched by the App Widget host with the {@link
android.appwidget.AppWidgetManager#ACTION_APPWIDGET_CONFIGURE ACTION_APPWIDGET_CONFIGURE} action,
so the Activity needs to accept this Intent. For example:</p>

<pre>
&lt;activity android:name=".ExampleAppWidgetConfigure">
    &lt;intent-filter>
        &lt;action android:name="android.appwidget.action.APPWIDGET_CONFIGURE" />
    &lt;/intent-filter>
&lt;/activity>
</pre>

<p>Also, the Activity must be declared in the AppWidgetProviderInfo XML file, with the 
<code>android:configure</code> attribute (see <a href="#MetaData">Adding 
the AppWidgetProviderInfo Metadata</a> above). For example, the configuration Activity
can be declared like this:</p>

<pre>
&lt;appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    ...
    android:configure="com.example.android.ExampleAppWidgetConfigure" 
    ... >
&lt;/appwidget-provider>
</pre>

<p>Notice that the Activity is declared with a fully-qualified namespace, because 
it will be referenced from outside your package scope.</p>

<p>That's all you need to get started with a configuration Activity. Now all you need is the actual
Activity. There are, however, two important things to remember when you implement the Activity:</p>
<ul>
  <li>The App Widget host calls the configuration Activity and the configuration Activity should always 
    return a result. The result should include the App Widget ID
    passed by the Intent that launched the Activity (saved in the Intent extras as
    {@link android.appwidget.AppWidgetManager#EXTRA_APPWIDGET_ID}).</li>
  <li>The {@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
    onUpdate()} method <strong>will not be called</strong> when the App Widget is created
    (the system will not send the ACTION_APPWIDGET_UPDATE broadcast when a configuration Activity
    is launched). It is the responsibility of the configuration Activity to request an update from the 
    AppWidgetManager when the App Widget is first created. However, 
    {@link android.appwidget.AppWidgetProvider#onUpdate(Context,AppWidgetManager,int[])
    onUpdate()} will be called for subsequent updates&mdash;it is only skipped the first time.</li>
</ul>

<p>See the code snippets in the following section for an example of how to return a result
from the configuration and update the App Widget.</p>


<h3 id="UpdatingFromTheConfiguration">Updating the App Widget from the configuration Activity</h3>

<p>When an App Widget uses a configuration Activity, it is the responsibility of the Activity
to update the App Widget when configuration is complete. 
You can do so by requesting an update directly from the 
{@link android.appwidget.AppWidgetManager}.</p>

<p>Here's a summary of the procedure to properly update the App Widget and close
the configuration Activity:</p>

<ol>
  <li>First, get the App Widget ID from the Intent that launched the Activity:
<pre>
Intent intent = getIntent();
Bundle extras = intent.getExtras();
if (extras != null) {
    mAppWidgetId = extras.getInt(
            AppWidgetManager.EXTRA_APPWIDGET_ID, 
            AppWidgetManager.INVALID_APPWIDGET_ID);
}
</pre>
  </li>
  <li>Perform your App Widget configuration.</li>
  <li>When the configuration is complete, get an instance of the AppWidgetManager by calling
    {@link android.appwidget.AppWidgetManager#getInstance(Context)}:
<pre>
AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
</pre>
  </li>
  <li>Update the App Widget with a {@link android.widget.RemoteViews} layout by calling
    {@link android.appwidget.AppWidgetManager#updateAppWidget(int,RemoteViews)}:
<pre>
RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.example_appwidget);
appWidgetManager.updateAppWidget(mAppWidgetId, views);
</pre>
  </li>
  <li>Finally, create the return Intent, set it with the Activity result, and finish the Activity:</li>
<pre>
Intent resultValue = new Intent();
resultValue.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, mAppWidgetId);
setResult(RESULT_OK, resultValue);
finish();
</pre>
  </li>
</ol>

<p class="note"><strong>Tip:</strong> When your configuration Activity first opens, set
the Activity result to RESULT_CANCELED. This way, if the user backs-out of the Activity before
reaching the end, the App Widget host is notified that the configuration was cancelled and the
App Widget will not be added.</p>

<p>See the <a 
href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/appwidget/ExampleAppWidgetConfigure.html">
ExampleAppWidgetConfigure.java</a> sample class in ApiDemos for an example.</p>