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">Layouts</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="@[+][<em>package</em>:]id/<em>resource_name</em>"
    android:layout_height=["<em>dimension</em>" | "fill_parent" | "wrap_content"]
    android:layout_width=["<em>dimension</em>" | "fill_parent" | "wrap_content"]
    [<em>ViewGroup-specific attributes</em>] &gt;
    &lt;<a href="#view-element"><em>View</em></a>
        android:id="@[+][<em>package</em>:]id/<em>resource_name</em>"
        android:layout_height=["<em>dimension</em>" | "fill_parent" | "wrap_content"]
        android:layout_width=["<em>dimension</em>" | "fill_parent" | "wrap_content"]
        [<em>View-specific 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;<a href="#include-element">include</a> layout="@layout/<i>layout_resource</i>"/&gt;
&lt;/<em>ViewGroup</em>&gt;
</pre>
<p class="note"><strong>Note:</strong> The root element can be either a
{@link android.view.ViewGroup}, a {@link android.view.View}, or a <a
href="#merge-element">{@code &lt;merge&gt;}</a> element, 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 ID</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. 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.html#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 ID</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. 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">Layouts</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>

  <dt id="include-element"><code>&lt;include&gt;</code></dt>
    <dd>Includes a layout file into this layout.
      <p class="caps">attributes:</p>
      <dl class="atn-list">
        <dt><code>layout</code></dt>
        <dd><em>Layout resource</em>. <strong>Required</strong>. Reference to a layout
resource.</dd>
        <dt><code>android:id</code></dt>
        <dd><em>Resource ID</em>. Overrides the ID given to the root view in the included layout.
        </dd>
        <dt><code>android:layout_height</code></dt>
        <dd><em>Dimension or keyword</em>. Overrides the height given to the root view in the
included layout. Only effective if <code>android:layout_width</code> is also declared.
        </dd>
        <dt><code>android:layout_width</code></dt>
        <dd><em>Dimension or keyword</em>. Overrides the width given to the root view in the
included layout. Only effective if <code>android:layout_height</code> is also declared.
        </dd>
      </dl>
      <p>You can include any other layout attributes in the <code>&lt;include&gt;</code> that are
supported by the root element in the included layout and they will override those defined in the
root element.</p>

    <p class="caution"><strong>Caution:</strong> If you want to override layout attributes using
      the <code>&lt;include&gt;</code> tag, you must override both
      <code>android:layout_height</code> and <code>android:layout_width</code> in order for
      other layout attributes to take effect.</p>

    <p>Another way to include a layout is to use {@link android.view.ViewStub}. It is a lightweight
View that consumes no layout space until you explicitly inflate it, at which point, it includes a
layout file defined by its {@code android:layout} attribute. For more information about using {@link
android.view.ViewStub}, read <a href="{@docRoot}training/improving-layouts/loading-ondemand.html">Loading
  Views On Demand</a>.</p>
    </dd>

  <dt id="merge-element"><code>&lt;merge&gt;</code></dt>
    <dd>An alternative root element that is not drawn in the layout hierarchy. Using this as the
root element is useful when you know that this layout will be placed into a layout
that already contains the appropriate parent View to contain the children of the
<code>&lt;merge&gt;</code> element. This is particularly useful when you plan to include this layout
in another layout file using <a href="#include-element"><code>&lt;include&gt;</code></a> and
this layout doesn't require a different {@link android.view.ViewGroup} container. For more
information about merging layouts, read <a
href="{@docRoot}training/improving-layouts/reusing-layouts.html">Re-using Layouts with &lt;include/></a>.</dd>

  </dl>



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

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

<p>However, if you have already defined an <a
href="{@docRoot}guide/topics/resources/drawable-resource.html#Id">ID resource</a> (and it is not
already used), then you can apply that ID to a {@link android.view.View} element by excluding the
plus symbol in the <code>android:id</code> value.</p>

<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,
see the <a href="{@docRoot}guide/topics/ui/custom-components.html">Custom Components</a> developer
guide.
</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">Layouts</a></li>
  <li>{@link android.view.View}</li>
  <li>{@link android.view.ViewGroup}</li>
</ul>
</dd>

</dl>