android_frameworks_base/docs/html/guide/topics/resources/layout-resource.jd

page.title=Layout Resource
parent.title=Resource Types
parent.link=available-resources.html
@jd:body

<div id="qv-wrapper">
  <div id="qv">
    <h2>See also</h2>
    <ol>
      <li><a href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring Layout</a></li>
    </ol>
  </div>
</div>

<p>A layout resource defines the architecture for the UI in an Activity or a component of a UI.</p>


<dl class="xml">

<dt>file location:</dt>
<dd><code>res/layout/<em>filename</em>.xml</code><br/>
The filename will be used as the resource ID.</dd>

<dt>compiled resource datatype:</dt>
<dd>Resource pointer to a {@link android.view.View} (or subclass) resource.</dd>

<dt>resource reference:</dt>
<dd>
In Java: <code>R.layout.<em>filename</em></code><br/>
In XML: <code>@[<em>package</em>:]layout/<em>filename</em></code>
</dd>

<dt>syntax:</dt>
<dd>
<pre class="stx">
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;<a href="#viewgroup-element"><em>ViewGroup</em></a> xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/<em>name</em>"
    android:layout_height="@+id/<em>string_name</em>"
    android:layout_width="@+id/<em>string_name</em>"
    [<em>other attributes</em>] &gt;
    &lt;<a href="#view-element"><em>View</em></a>
        android:id="@+id/<em>name</em>"
        android:layout_height="@+id/<em>string_name</em>"
        android:layout_width="@+id/<em>string_name</em>"
        [<em>other attributes</em>] &gt;
        &lt;<a href="#requestfocus-element">requestFocus</a>/&gt;
    &lt;/<em>View</em>&gt;
    &lt;<a href="#viewgroup-element"><em>ViewGroup</em></a> &gt;
        &lt;<a href="#view-element"><em>View</em></a> /&gt;
    &lt;/<em>ViewGroup</em>&gt;
&lt;/<em>ViewGroup</em>&gt;
</pre>
<p class="note"><strong>Note:</strong> The root element can be either a
{@link android.view.ViewGroup} or a {@link android.view.View}, but there must be only
one root element and it must contain the {@code xmlns:android} attribute with the {@code android}
namespace as shown.</p>
</dd>

<dt>elements:</dt>
<dd>
  <dl class="tag-list">

  <dt id="viewgroup-element"><code>&lt;ViewGroup&gt;</code></dt>
    <dd>A container for other {@link android.view.View} elements. There are many
    different kinds of {@link android.view.ViewGroup} objects and each one lets you
    specify the layout of the child elements in different ways. Different kinds of
    {@link android.view.ViewGroup} objects include {@link android.widget.LinearLayout},
    {@link android.widget.RelativeLayout}, and {@link android.widget.FrameLayout}.
    <p>You should not assume that any derivation of {@link android.view.ViewGroup}
    will accept nested {@link android.view.View}s. Some {@link android.view.ViewGroup}s
    are implementations of the {@link android.widget.AdapterView} class, which determines
    its children only from an {@link android.widget.Adapter}.</p>
      <p class="caps">attributes:</p>
      <dl class="atn-list">
        <dt><code>android:id</code></dt>
        <dd><em>Resource name</em>. A unique resource name for the element, which you can
use to obtain a reference to the {@link android.view.ViewGroup} from your application.
          The value takes the form: <code>"@+id/<em>name</em>"</code>. See more about the
          <a href="#idvalue">value for {@code android:id}</a> below.
        </dd>
        <dt><code>android:layout_height</code></dt>
        <dd><em>Dimension or keyword</em>. <strong>Required</strong>. The height for the group, as a
dimension value (or <a
href="more-resources.html#Dimension">dimension resource</a>) or a keyword ({@code "fill_parent"}
or {@code "wrap_content"}). See the <a href="#layoutvalues">valid values</a> below.
        </dd>
        <dt><code>android:layout_width</code></dt>
        <dd><em>Dimension or keyword</em>. <strong>Required</strong>. The width for the group, as a
dimension value (or <a
href="more-resources.html#Dimension">dimension resource</a>) or a keyword ({@code "fill_parent"}
or {@code "wrap_content"}). See the <a href="#layoutvalues">valid values</a> below.
        </dd>
      </dl>
      <p>More attributes are supported by the {@link android.view.ViewGroup}
      base class, and many more are supported by each implementation of
      {@link android.view.ViewGroup}. For a reference of all available attributes,
      see the corresponding reference documentation for the {@link android.view.ViewGroup} class
(for example, the <a
      href="{@docRoot}reference/android/widget/LinearLayout#lattrs">LinearLayout XML attributes</a>).</p>
    </dd>
  <dt id="view-element"><code>&lt;View&gt;</code></dt>
    <dd>An individual UI component, generally referred to as a "widget". Different
    kinds of {@link android.view.View} objects include {@link android.widget.TextView},
    {@link android.widget.Button}, and {@link android.widget.CheckBox}.
      <p class="caps">attributes:</p>
      <dl class="atn-list">
        <dt><code>android:id</code></dt>
        <dd><em>Resource name</em>. A unique resource name for the element, which you can use to
          obtain a reference to the {@link android.view.View} from your application.
          The value takes the form: <code>"@+id/<em>name</em>"</code>. See more about the
          <a href="#idvalue">value for {@code android:id}</a> below.
        </dd>
        <dt><code>android:layout_height</code></dt>
        <dd><em>Dimension or keyword</em>. <strong>Required</strong>. The height for the element, as
a dimension value (or <a
href="more-resources.html#Dimension">dimension resource</a>) or a keyword ({@code "fill_parent"}
or {@code "wrap_content"}). See the <a href="#layoutvalues">valid values</a> below.
        </dd>
        <dt><code>android:layout_width</code></dt>
        <dd><em>Dimension or keyword</em>. <strong>Required</strong>. The width for the element, as
a dimension value (or <a
href="more-resources.html#Dimension">dimension resource</a>) or a keyword ({@code "fill_parent"}
or {@code "wrap_content"}). See the <a href="#layoutvalues">valid values</a> below.
        </dd>
      </dl>
      <p>More attributes are supported by the {@link android.view.View}
      base class, and many more are supported by each implementation of
      {@link android.view.View}. Read <a href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring
      Layout</a> for more information. For a reference of all available attributes,
      see the corresponding reference documentation (for example, the <a
      href="{@docRoot}reference/android/widget/TextView.html#lattrs">TextView XML attributes</a>).</p>
    </dd>
  <dt id="requestfocus-element"><code>&lt;requestFocus&gt;</code></dt>
    <dd>Any element representing a {@link android.view.View} object can include this empty element,
    which gives it's parent initial focus on the screen. You can have only one of these
    elements per file.</dd>

  </dl>

<h4 id="idvalue">Value for <code>android:id</code></h4>

<p>For the ID value, you should use this syntax form: <code>"@+id/<em>name</em>"</code>. The plus symbol,
{@code +}, indicates that this is a new resource ID and the aapt tool will create
a new resource number to the {@code R.java} class, if it doesn't already exist. For example:</p>
<pre>
&lt;TextView android:id="@+id/nameTextbox"/>
</pre>
<p>You can then refer to it this way in Java:</p>
<pre>
findViewById(R.id.nameTextbox);
</pre>

<h4 id="layoutvalues">Value for <code>android:layout_height</code> and
<code>android:layout_width</code>:</h4>

  <p>The height and width value can be expressed using any of the
  <a href="more-resources.html#Dimension">dimension
  units</a> supported by Android (px, dp, sp, pt, in, mm) or with the following keywords:</p>
  <table><tr><th>Value</th><th>Description</th></tr>
    <tr>
      <td><code>match_parent</code></td>
      <td>Sets the dimension to match that of the parent element. Added in API Level 8 to
deprecate <code>fill_parent</code>.</td>
    </tr>
    <tr>
      <td><code>fill_parent</code></td>
      <td>Sets the dimension to match that of the parent element.</td>
    </tr><tr>
      <td><code>wrap_content</code></td>
      <td>Sets the dimension only to the size required to fit the content of this element.</td>
    </tr>
  </table>

<h4>Custom View elements</h4>

<p>You can create your own custom {@link android.view.View} and {@link android.view.ViewGroup}
elements and apply them to your layout the same as a standard layout
element. You can also specify the attributes supported in the XML element. To learn more,
read <a href="{@docRoot}guide/topics/ui/custom-components.html">Building Custom Components</a>.
</p>

</dd> <!-- end  elements and attributes -->

<dt>example:</dt>
<dd>XML file saved at <code>res/layout/main_activity.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="fill_parent" 
              android:layout_height="fill_parent" 
              android:orientation="vertical" >
    &lt;TextView android:id="@+id/text"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Hello, I am a TextView" />
    &lt;Button android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, I am a Button" />
&lt;/LinearLayout>
</pre>
    <p>This application code will load the layout for an {@link android.app.Activity}, in the
    {@link android.app.Activity#onCreate(Bundle) onCreate()} method:</dt>
    <dd>
<pre>
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView.(R.layout.main_activity);
}
</pre>
</dd> <!-- end example -->


<dt>see also:</dt>
<dd>
<ul>
  <li><a href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring Layout</a></li>
  <li>{@link android.view.View}</li>
  <li>{@link android.view.ViewGroup}</li>
</ul>
</dd>

</dl>