xref: /frameworks/base/docs/html/guide/topics/resources/accessing-resources.jd

page.title=Accessing Resources
parent.title=Application Resources
parent.link=index.html
@jd:body

<div id="qv-wrapper">
<div id="qv">
  <h2>Quickview</h2>
  <ul>
    <li>Resources can be referenced from code using integers from {@code R.java}, such as
{@code R.drawable.myimage}</li>
    <li>Resources can be referenced from resources using a special XML syntax, such as {@code
&#64;drawable/myimage}</li>
    <li>You can also access your app resources with methods in
{@link android.content.res.Resources}</li>
  </ul>

  <h2>Key classes</h2>
  <ol>
    <li>{@link android.content.res.Resources}</li>
  </ol>

  <h2>In this document</h2>
  <ol>
    <li><a href="#ResourcesFromCode">Accessing Resources from Code</a></li>
    <li><a href="#ResourcesFromXml">Accessing Resources from XML</a>
      <ol>
        <li><a href="#ReferencesToThemeAttributes">Referencing style attributes</a></li>
      </ol>
    </li>
    <li><a href="#PlatformResources">Accessing Platform Resources</a></li>
  </ol>

  <h2>See also</h2>
  <ol>
    <li><a href="providing-resources.html">Providing Resources</a></li>
    <li><a href="available-resources.html">Resource Types</a></li>
  </ol>
</div>
</div>




<p>Once you provide a resource in your application (discussed in <a
href="providing-resources.html">Providing Resources</a>), you can apply it by
referencing its resource ID. All resource IDs are defined in your project's {@code R} class, which
the {@code aapt} tool automatically generates.</p>

<p>When your application is compiled, {@code aapt} generates the {@code R} class, which contains
resource IDs for all the resources in your {@code
res/} directory. For each type of resource, there is an {@code R} subclass (for example,
{@code R.drawable} for all drawable resources) and for each resource of that type, there is a static
integer (for example, {@code R.drawable.icon}). This integer is the resource ID that you can use
to retrieve your resource.</p>

<p>Although the {@code R} class is where resource IDs are specified, you should never need to
look there to discover a resource ID. A resource ID is always composed of:</p>
<ul>
  <li>The <em>resource type</em>: Each resource is grouped into a "type," such as {@code
string}, {@code drawable}, and {@code layout}. For more about the different types, see <a
href="available-resources.html">Resource Types</a>.
  </li>
  <li>The <em>resource name</em>, which is either: the filename,
excluding the extension; or the value in the XML {@code android:name} attribute, if the
resource is a simple value (such as a string).</li>
</ul>

<p>There are two ways you can access a resource:</p>
<ul>
  <li><strong>In code:</strong> Using an static integer from a sub-class of your {@code R}
class, such as:
    <pre class="classic no-pretty-print">R.string.hello</pre>
    <p>{@code string} is the resource type and {@code hello} is the resource name. There are many
Android APIs that can access your resources when you provide a resource ID in this format. See
<a href="#ResourcesFromCode">Accessing Resources in Code</a>.</p>
  </li>
  <li><strong>In XML:</strong> Using a special XML syntax that also corresponds to
the resource ID defined in your {@code R} class, such as:
    <pre class="classic no-pretty-print">&#64;string/hello</pre>
    <p>{@code string} is the resource type and {@code hello} is the resource name. You can use this
syntax in an XML resource any place where a value is expected that you provide in a resource. See <a
href="#ResourcesFromXml">Accessing Resources from XML</a>.</p>
  </li>
</ul>



<h2 id="ResourcesFromCode">Accessing Resources in Code </h2>

<p>You can use a resource in code by passing the resource ID as a method parameter. For
example, you can set an {@link android.widget.ImageView} to use the {@code res/drawable/myimage.png}
resource using {@link android.widget.ImageView#setImageResource(int) setImageResource()}:</p>
<pre>
ImageView imageView = (ImageView) findViewById(R.id.myimageview);
imageView.setImageResource(<strong>R.drawable.myimage</strong>);
</pre>

<p>You can also retrieve individual resources using methods in {@link
android.content.res.Resources}, which you can get an instance of
with {@link android.content.Context#getResources()}.</p>

<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Access to Original Files</h2>

<p>While uncommon, you might need access your original files and directories. If you do, then
saving your files in {@code res/} won't work for you, because the only way to read a resource from
{@code res/} is with the resource ID. Instead, you can save your resources in the
{@code assets/} directory.</p>
<p>Files saved in the {@code assets/} directory are <em>not</em> given a resource
ID, so you can't reference them through the {@code R} class or from XML resources. Instead, you can
query files in the {@code assets/} directory like a normal file system and read raw data using
{@link android.content.res.AssetManager}.</p>
<p>However, if all you require is the ability to read raw data (such as a video or audio file),
then save the file in the {@code res/raw/} directory and read a stream of bytes using {@link
android.content.res.Resources#openRawResource(int) openRawResource()}.</p>

</div>
</div>


<h3>Syntax</h3>

<p>Here's the syntax to reference a resource in code:</p>

<pre class="classic no-pretty-print">
[<em>&lt;package_name&gt;</em>.]R.<em>&lt;resource_type&gt;</em>.<em>&lt;resource_name&gt;</em>
</pre>

<ul>
  <li><em>{@code &lt;package_name&gt;}</em> is the name of the package in which the resource is located (not
required when referencing resources from your own package).</li>
  <li><em>{@code &lt;resource_type&gt;}</em> is the {@code R} subclass for the resource type.</li>
  <li><em>{@code &lt;resource_name&gt;}</em> is either the resource filename
without the extension or the {@code android:name} attribute value in the XML element (for simple
values).</li>
</ul>
<p>See <a href="available-resources.html">Resource Types</a> for
more information about each resource type and how to reference them.</p>


<h3>Use cases</h3>

<p>There are many methods that accept a resource ID parameter and you can retrieve resources using
methods in {@link android.content.res.Resources}. You can get an instance of  {@link
android.content.res.Resources} with {@link android.content.Context#getResources
Context.getResources()}.</p>


<p>Here are some examples of accessing resources in code:</p>

<pre>
// Load a background for the current screen from a drawable resource
{@link android.app.Activity#getWindow()}.{@link
android.view.Window#setBackgroundDrawableResource(int)
setBackgroundDrawableResource}(<strong>R.drawable.my_background_image</strong>) ;

// Set the Activity title by getting a string from the Resources object, because
//  this method requires a CharSequence rather than a resource ID
{@link android.app.Activity#getWindow()}.{@link android.view.Window#setTitle(CharSequence)
setTitle}(getResources().{@link android.content.res.Resources#getText(int)
getText}(<strong>R.string.main_title</strong>));

// Load a custom layout for the current screen
{@link android.app.Activity#setContentView(int)
setContentView}(<strong>R.layout.main_screen</strong>);

// Set a slide in animation by getting an Animation from the Resources object
mFlipper.{@link android.widget.ViewAnimator#setInAnimation(Animation)
setInAnimation}(AnimationUtils.loadAnimation(this,
        <strong>R.anim.hyperspace_in</strong>));

// Set the text on a TextView object using a resource ID
TextView msgTextView = (TextView) findViewById(<strong>R.id.msg</strong>);
msgTextView.{@link android.widget.TextView#setText(int)
setText}(<strong>R.string.hello_message</strong>);
</pre>


<p class="caution"><strong>Caution:</strong> You should never modify the {@code
R.java} file by hand&mdash;it is generated by the {@code aapt} tool when your project is
compiled. Any changes are overridden next time you compile.</p>



<h2 id="ResourcesFromXml">Accessing Resources from XML</h2>

<p>You can define values for some XML attributes and elements using a
reference to an existing resource. You will often do this when creating layout files, to
supply strings and images for your widgets.</p>

<p>For example, if you add a {@link android.widget.Button} to your layout, you should use
a <a href="string-resource.html">string resource</a> for the button text:</p>

<pre>
&lt;Button
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="<strong>@string/submit</strong>" /&gt;
</pre>


<h3>Syntax</h3>

<p>Here is the syntax to reference a resource in an XML resource:</p>

<pre class="classic no-pretty-print">
&#64;[<em>&lt;package_name&gt;</em>:]<em>&lt;resource_type&gt;</em>/<em>&lt;resource_name&gt;</em>
</pre>

<ul>
  <li>{@code &lt;package_name&gt;} is the name of the package in which the resource is located (not
required when referencing resources from the same package)</li>
  <li>{@code &lt;resource_type&gt;} is the
{@code R} subclass for the resource type</li>
  <li>{@code &lt;resource_name&gt;} is either the resource filename
without the extension or the {@code android:name} attribute value in the XML element (for simple
values).</li>
</ul>

<p>See <a href="available-resources.html">Resource Types</a> for
more information about each resource type and how to reference them.</p>


<h3>Use cases</h3>

<p>In some cases you must use a resource for a value in XML (for example, to apply a drawable image
to a widget), but you can also use a resource in XML any place that accepts a simple value. For
example, if you have the following resource file that includes a <a
href="more-resources.html#Color">color resource</a> and a <a
href="string-resource.html">string resource</a>:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;resources>
   &lt;color name="opaque_red">#f00&lt;/color>
   &lt;string name="hello">Hello!&lt;/string>
&lt;/resources>
</pre>

<p>You can use these resources in the following layout file to set the text color and
text string:</p>

<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText xmlns:android=&quot;http://schemas.android.com/apk/res/android";
    android:layout_width=&quot;fill_parent&quot;
    android:layout_height=&quot;fill_parent&quot;
    android:textColor=&quot;<strong>&#64;color/opaque_red</strong>&quot;
    android:text=&quot;<strong>&#64;string/hello</strong>&quot; /&gt;
</pre>

<p>In this case you don't need to specify the package name in the resource reference because the
resources are from your own package. To
reference a system resource, you would need to include the package name. For example:</p>

<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText xmlns:android=&quot;http://schemas.android.com/apk/res/android";
    android:layout_width=&quot;fill_parent&quot;
    android:layout_height=&quot;fill_parent&quot;
    android:textColor=&quot;<strong>&#64;android:color/secondary_text_dark</strong>&quot;
    android:text=&quot;&#64;string/hello&quot; /&gt;
</pre>

<p class="note"><strong>Note:</strong> You should use string resources at all times, so that your
application can be localized for other languages. For information about creating alternative
resources (such as localized strings), see <a
href="providing-resources.html#AlternativeResources">Providing Alternative
Resources</a>.</p>

<p>You can even use resources in XML to create aliases. For example, you can create a
drawable resource that is an alias for another drawable resource:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/other_drawable" />
</pre>

<p>This sounds redundant, but can be very useful when using alternative resource. Read more about
<a href="providing-resources.html#AliasResources">Creating alias resources</a>.</p>



<h3 id="ReferencesToThemeAttributes">Referencing style attributes</h3>

<p>A style attribute resource allows you to reference the value
of an attribute in the currently-applied theme. Referencing a style attribute allows you to
customize the look of UI elements by styling them to match standard variations supplied by the
current theme, instead of supplying a hard-coded value. Referencing a style attribute
essentially says, "use the style that is defined by this attribute, in the current theme."</p>

<p>To reference a style attribute, the name syntax is almost identical to the normal resource
format, but instead of the at-symbol ({@code &#64;}), use a question-mark ({@code ?}), and the
resource type portion is optional. For instance:</p>

<pre class="classic">
?[<em>&lt;package_name&gt;</em>:][<em>&lt;resource_type&gt;</em>/]<em>&lt;resource_name&gt;</em>
</pre>

<p>For example, here's how you can reference an attribute to set the text color to match the
"primary" text color of the system theme:</p>

<pre>
&lt;EditText id=&quot;text&quot;
    android:layout_width=&quot;fill_parent&quot;
    android:layout_height=&quot;wrap_content&quot;
    android:textColor=&quot;<strong>?android:textColorSecondary</strong>&quot;
    android:text=&quot;&#64;string/hello_world&quot; /&gt;
</pre>

<p>Here, the {@code android:textColor} attribute specifies the name of a style attribute
in the current theme. Android now uses the value applied to the {@code android:textColorSecondary}
style attribute as the value for {@code android:textColor} in this widget. Because the system
resource tool knows that an attribute resource is expected in this context,
you do not need to explicitly state the type (which would be
<code>?android:attr/textColorSecondary</code>)&mdash;you can exclude the {@code attr} type.</p>




<h2 id="PlatformResources">Accessing Platform Resources</h2>

<p>Android contains a number of standard resources, such as styles, themes, and layouts. To
access these resource, qualify your resource reference with the
<code>android</code> package name. For example, Android provides a layout resource you can use for
list items in a {@link android.widget.ListAdapter}:</p>

<pre>
{@link android.app.ListActivity#setListAdapter(ListAdapter)
setListAdapter}(new {@link
android.widget.ArrayAdapter}&lt;String&gt;(this, <strong>android.R.layout.simple_list_item_1</strong>, myarray));
</pre>

<p>In this example, {@link android.R.layout#simple_list_item_1} is a layout resource defined by the
platform for items in a {@link android.widget.ListView}. You can use this instead of creating
your own layout for list items. For more information, see the
<a href="{@docRoot}guide/topics/ui/layout/listview.html">List View</a> developer guide.</p>