M7350/base/docs/html/guide/topics/ui/themes.jd

page.title=Applying Styles and Themes
parent.title=User Interface
parent.link=index.html
@jd:body

<div id="qv-wrapper">
<div id="qv">
  <h2>In this document</h2>
  <ol>
    <li><a href="#DefiningStyles">Defining Styles</a>
      <ol>
        <li><a href="#Inheritance">Inheritance</a></li>
        <li><a href="#Properties">Style Properties</a></li>
      </ol>
    </li>
    <li><a href="#ApplyingStyles">Applying Styles and Themes to the UI</a>
      <ol>
        <li><a href="#ApplyAStyle">Apply a style to a View</a></li>
        <li><a href="#ApplyATheme">Apply a theme to an Activity or application</a></li>
      </ol>
    </li>
    <li><a href="#PlatformStyles">Using Platform Styles and Themes</a></li>
  </ol>
  <h2>See also</h2>
  <ol>
    <li><a href="{@docRoot}guide/topics/resources/available-resources.html#stylesandthemes">Style
    and Theme Resources</a></li>
    <li>{@link android.R.style} for Android styles and themes</li>
    <li>{@link android.R.attr} for all style attributes</li>
  </ol>
</div>
</div>


<p>A <strong>style</strong> is a collection of properties that
specify the look and format for a {@link android.view.View} or window.
A style can specify properties such as height, padding, font color, font size,
background color, and much more. A style is defined in an XML resource that is
separate from the XML that specifies the layout.</p>

<p>Styles in Android share a similar philosophy to cascading stylesheets in web
design&mdash;they allow you to separate the design from the
content.</p>

<p>For example, by using a style, you can take this layout XML:</p>
<pre>
&lt;TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:textColor="#00FF00"
    android:typeface="monospace"
    android:text="@string/hello" />
</pre>
<p>And turn it into this:</p>
<pre>
&lt;TextView
    style="@style/CodeFont"
    android:text="@string/hello" />
</pre>

<p>All of the attributes related to style have been removed from the layout XML and put into a
style definition called {@code CodeFont}, which is then applied with the <code>style</code>
attribute. You'll see the definition for this style in the following section.</p>

<p>A <strong>theme</strong> is a style applied to an entire {@link android.app.Activity} or
application, rather than an individual {@link android.view.View} (as in the example above). When a
style is applied as a theme, every View in the Activity or application will apply each style
property that it supports. For example, you can apply the same {@code CodeFont} style
as a theme for an Activity and then all text inside that Activity will have green monospace
font.</p>


<h2 id="DefiningStyles">Defining Styles</h2>

<p>To create a set of styles, save an XML file in the {@code res/values/}
directory of your project. The name of the XML file is arbitrary, but it must use the
{@code .xml} extension and be saved in the {@code res/values/} folder.</p>

<p>The root node of the XML file must be {@code &lt;resources&gt;}.</p>

<p>For each style you want to create, add a {@code &lt;style>} element to the file
with a {@code name} that uniquely identifies the style (this attribute is required).
Then add an {@code &lt;item>} element for each property of that style, with a
{@code name} that declares the style property and a value to go with it (this attribute
is required). The value for the {@code &lt;item>} can
be a keyword string, a hex color, a reference to another resource type, or other value
depending on the style property.
Here's an example file with a single style:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;resources&gt;
    &lt;style name="CodeFont" parent="@android:style/TextAppearance.Medium"&gt;
        &lt;item name="android:layout_width"&gt;fill_parent&lt;/item&gt;
        &lt;item name="android:layout_height"&gt;wrap_content&lt;/item&gt;
        &lt;item name="android:textColor"&gt;#00FF00&lt;/item&gt;
        &lt;item name="android:typeface"&gt;monospace&lt;/item&gt;
    &lt;/style&gt;
&lt;/resources&gt;
</pre>

<p>Each child of the {@code &lt;resources>} element is converted into an application resource
object at compile-time, which can be referenced by the value in the {@code &lt;style>} element's
{@code name} attribute. This example style can be referenced from an XML layout as
{@code @style/CodeFont} (as demonstrated in the introduction above).</p>

<p>The <code>parent</code> attribute in the {@code &lt;style>} element is optional and
specifies the resource ID of another style from which this style should inherit
properties. You can then override the inherited style properties if you want to.</p>

<p>Remember, a style that you want to use as an Activity or application theme is defined in XML
exactly the same as a style for a View. A style such as the one defined above can be applied as a
style for a single View or as a theme for an entire Activity or application. How to apply a style
for a single View or as an application theme is discussed later.</p>


<h3 id="Inheritance">Inheritance</h3>

<p>The {@code parent} attribute in the {@code &lt;style>} element lets you specify a style
from which your style should inherit properties.
You can use this to inherit properties from an existing style and
then define only the properties that you want to change or add. You can
inherit from styles that you've created yourself or from styles that are built into the
platform. (See <a href="#PlatformStyles">Using Platform Styles and Themes</a>, below, for
information about inheriting from styles defined by the Android platform.) For example, you can
inherit the Android platform's default text appearance and then modify it:</p>

<pre>
    &lt;style name="GreenText" parent="@android:style/TextAppearance"&gt;
        &lt;item name="android:textColor"&gt;#00FF00&lt;/item&gt;
    &lt;/style&gt;
</pre>

<p>If you want to inherit from styles that you've defined yourself, you <em>do not</em> have to use
the <code>parent</code> attribute. Instead, just prefix the name of the style you want to
inherit to the name of your new style, separated by a period. For example, to create a new style
that inherits the <code>CodeFont</code> style defined above, but make the color red,
you can author the new style like this:</p>

<pre>
    &lt;style name="CodeFont.Red"&gt;
        &lt;item name="android:textColor"&gt;#FF0000&lt;/item&gt;
    &lt;/style&gt;
</pre>

<p>Notice that there is no {@code parent} attribute in the {@code &lt;style&gt;} tag, but because
the {@code name} attribute begins with the {@code CodeFont} style name (which
is a style that you have created), this style inherits all style properties from that style. This
style then overrides the {@code android:textColor} property to make the text red. You can
reference this new style as {@code @style/CodeFont.Red}.</p>

<p>You can continue inheriting like
this as many times as you'd like, by chaining names with periods. For example, you can
extend {@code CodeFont.Red} to be bigger, with:</p>
<pre>
    &lt;style name="CodeFont.Red.Big"&gt;
        &lt;item name="android:textSize"&gt;30sp&lt;/item&gt;
    &lt;/style&gt;
</pre>
<p>This inherits from both {@code CodeFont} and {@code CodeFont.Red} styles, then adds the
{@code android:textSize} property.</p>

<p class="note"><strong>Note:</strong> This technique for inheritance by chaining together
names only works for styles defined by your own resources. You can't inherit Android built-in styles
this way. To reference a built-in style, such as {@link android.R.style#TextAppearance}, you must
use the {@code parent} attribute.</p>


<h3 id="Properties">Style Properties</h3>

<p>Now that you understand how a style is defined, you need to learn what kind
of style properties&mdash;defined by the {@code &lt;item>} element&mdash;are available.
You're probably familiar with some already, such as {@link android.R.attr#layout_width} and
{@link android.R.attr#textColor}. Of course, there are many more style properties you can use.</p>

<p>The best place to find properties that apply to a specific {@link android.view.View} is the
corresponding class reference, which lists all of the supported XML attributes. For example, all of the
attributes listed in the table of
<a href="{@docRoot}reference/android/widget/TextView.html#lattrs">TextView XML 
attributes</a> can be used in a style definition for a {@link android.widget.TextView} element (or one of
its subclasses). One of the attributes listed in the reference is <a
href="{@docRoot}reference/android/widget/TextView.html#attr_android:inputType">{@code
android:inputType}</a>, so where you might normally place the <a
href="{@docRoot}reference/android/widget/TextView.html#attr_android:inputType">{@code
android:inputType}</a>
attribute in an {@code &lt;EditText>} element, like this:</p>
<pre>
&lt;EditText
    android:inputType="number"
    ... />
</pre>

<p>You can instead create a style for the {@link android.widget.EditText} element that includes this property:</p>
<pre>
&lt;style name="Numbers">
  &lt;item name="android:inputType">number&lt;/item>
  ...
&lt;/style>
</pre>
<p>So your XML for the layout can now implement this style:</p>
<pre>
&lt;EditText
    style="@style/Numbers"
    ... />
</pre>

<p>This simple example may look like more work, but when you add more style properties and
factor-in the ability to re-use the style in various places, the pay-off can be huge.</p>

<p>For a reference of all available style properties, see the {@link android.R.attr}
reference. Keep in mind that all View objects don't accept all the same style attributes, so you
should normally refer to the specific {@link android.view.View} class for supported style
properties. However, if you
apply a style to a View that does not support all of the style properties, the View will
apply only those properties that are supported and simply ignore the others.</p>

<p>Some style properties, however, are not supported by any View element and can only be applied
as a theme. These style properties apply to the entire window and not to any type of View.
For example, style properties for a theme can hide the application title, hide the status bar,
or change the window's background. These kind of style properties do not belong to any View object.
To discover these theme-only style properties, look at the {@link android.R.attr} reference for
attributes that begin with {@code window}. For instance, {@code windowNoTitle} and {@code
windowBackground} are style properties that are effective only when the style is applied as
a theme to an Activity or application. See the next section for information about applying a
style as a theme.</p>

<p class="note"><strong>Note:</strong> Don't forget to prefix the property names in each
{@code &lt;item&gt;} element with the <code>android:</code> namespace. For example:
{@code &lt;item name="android:inputType">}.</p>



<h2 id="ApplyingStyles">Applying Styles and Themes to the UI</h2>

<p>There are two ways to set a style:</p>
<ul>
  <li>To an individual View, by adding the <code>style</code> attribute to a View
  element in the XML for your layout.</li>
  <li>Or, to an entire Activity or application, by adding the <code>android:theme</code>
  attribute to the <code>&lt;activity></code> or <code>&lt;application></code> element
  in the Android manifest.</li>
</ul>

<p>When you apply a style to a single {@link android.view.View} in the layout, the properties
defined by the style are applied only to that {@link android.view.View}. If a style is applied to a
{@link android.view.ViewGroup}, the child {@link android.view.View} elements will
<strong>not</strong> inherit the style properties&mdash;only the element to which you directly apply
the style will apply its properties. However, you <em>can</em> apply a style so that it
applies to all {@link android.view.View} elements&mdash;by applying the style as a theme.</p>

<p>To apply a style definition as a theme, you must apply the style to an
{@link android.app.Activity} or application in the Android manifest. When you do so,
every {@link android.view.View} within the Activity or
application will apply each property that it supports. For example, if you apply the {@code
CodeFont} style from the previous examples to an Activity, then all View elements
that support the text style properties will apply them. Any View that does not support
the properties will ignore them. If a View supports only some of the properties, then
it will apply only those properties.</p>


<h3 id="ApplyAStyle">Apply a style to a View</h3>

<p>Here's how to set a style for a View in the XML layout:</p>

<pre>
&lt;TextView
    style="@style/CodeFont"
    android:text="@string/hello" />
</pre>

<p>Now this TextView will be styled as defined by the style named {@code CodeFont}.
(See the sample above, in <a href="#DefiningStyles">Defining Styles</a>.)</p>

<p class="note"><strong>Note:</strong> The <code>style</code> attribute
does <em>not</em> use the <code>android:</code> namespace prefix.</p>


<h3 id="ApplyATheme">Apply a theme to an Activity or application</h3>

<p>To set a theme for all the activities of your application, open the {@code AndroidManifest.xml} file and
edit the <code>&lt;application></code> tag to include the <code>android:theme</code> attribute with the 
style name. For example:</p>

<pre>
&lt;application android:theme="@style/CustomTheme">
</pre>

<p>If you want a theme applied to just one Activity in your application, then add the 
<code>android:theme</code> attribute to the <code>&lt;activity></code> tag instead.</p>

<p>Just as Android provides other built-in resources, there are many pre-defined themes that you can use, to avoid
writing them yourself. For example, you can use the {@code Dialog} theme and make your Activity
appear like a dialog box:</p>

<pre>
&lt;activity android:theme="@android:style/Theme.Dialog">
</pre>

<p>Or if you want the background to be transparent, use the Translucent theme:</p>

<pre>
&lt;activity android:theme="@android:style/Theme.Translucent">
</pre>

<p>If you like a theme, but want to tweak it, just add the theme as the <code>parent</code>
of your custom theme. For example, you can modify the traditional dialog theme to use your own
background image like this:</p>
<pre>
&lt;style name="CustomDialogTheme" parent="@android:style/Theme.Dialog">
    &lt;item name="android:windowBackground">@drawable/custom_dialog_background&lt;/item>
&lt;/style>
</pre>

<p>Now use {@code CustomDialogTheme} instead of {@code Theme.Dialog} inside the Android
Manifest:</p>

<pre>
&lt;activity android:theme="@style/CustomDialogTheme">
</pre>


<!-- This currently has some bugs

<h3 id="setThemeFromTheApp">Set the theme from the application</h3>

<p>We recommend that you set your themes in you Android manifest, as described above, because it's simple and
keeps your program code focused on application functionality, rather than style. But if it's necessary
for you to change your theme programatically (perhaps based on a user preference), you can.</p>

<p>To set the theme in your program code, use the {@link android.content.ContextWrapper#setTheme(int)}
method and pass it the theme resource ID. Note that, when doing so, you must be sure to set the theme <em>before</em> 
instantiating any Views in the context, for example, before calling 
<code>setContentView(View)</code> or <code>inflate(int, ViewGroup)</code>. This ensures that 
the system applies the same theme for all of your UI screens. Here's an example:</p>

<pre>
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
    setTheme(android.R.style.Theme_Light);
    setContentView(R.layout.linear_layout_3);
}
</pre>

<p>If you are considering loading a theme programmatically for the main
screen of your application, note that the theme would not be applied
in any animations the system would use to start the activity, which
would take place before your application opens. In most cases, if 
you want to apply a theme to your main screen, doing so in XML
 is a better approach. </p>

-->



<h2 id="PlatformStyles">Using Platform Styles and Themes</h2>

<p>The Android platform provides a large collection of styles and themes that you can
use in your applications. You can find a reference of all available styles in the
{@link android.R.style} class. To use the styles listed here, replace all underscores in
the style name with a period. For example, you can apply the
{@link android.R.style#Theme_NoTitleBar} theme with
{@code "@android:style/Theme.NoTitleBar"}.</p>

<p>The {@link android.R.style} reference, however, is not well documented and does not
thoroughly describe the styles, so viewing the actual source code for these styles and
themes will give you a better understanding of what style properties each one provides.
For a better reference to the Android styles and themes, see the following source code:</p>
<ul>
	<li><a href="http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;f=core/res/res/values/styles.xml;h=d7b654e49809cb97a35682754b1394af5c8bc88b;hb=HEAD">Android Styles (styles.xml)</a></li>
	<li><a href="http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;f=core/res/res/values/themes.xml;h=6b3d7407d1c895a3c297e60d5beac98e2d34c271;hb=HEAD">Android Themes (themes.xml)</a></li>
</ul>

<p>These files will help you learn through example. For instance, in the Android themes source code,
you'll find a declaration for <code>&lt;style name="Theme.Dialog"&gt;</code>. In this definition,
you'll see all of the properties that are used to style dialogs that are used by the Android
framework.</p>

<p>For more information about the syntax used to create styles in XML, see
<a href="{@docRoot}guide/topics/resources/available-resources.html#stylesandthemes">Available Resource Types:
Style and Themes</a>.</p>

<p>For a reference of available style attributes that you can use to define a style or theme
(e.g., "windowBackground" or "textAppearance"), see {@link android.R.attr} or the respective
View class for which you are creating a style.</p>