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page.title=Resources and Internationalization
parent.title=Resources and Assets
parent.link=index.html
@jd:body
<div id="qv-wrapper">
<div id="qv">
<h2>Key classes</h2>
<ol>
<li>{@link android.content.res.Resources}</li>
</ol>
<h2>In this document</h2>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#CreatingResources">Creating Resources</a></li>
<li><a href="#UsingResources">Using Resources</a>
<ol>
<li><a href="#ResourcesInCode">Using Resources in Code</a></li>
<li><a href="#ReferencesToResources">References to Resources</a></li>
<li><a href="#ReferencesToThemeAttributes">References to Theme Attributes</a></li>
<li><a href="#UsingSystemResources">Using System Resources</a></li>
</ol>
</li>
<li><a href="#AlternateResources">Alternate Resources</a></li>
<li><a href="#ResourcesTerminology">Terminology</a></li>
<li><a href="#i18n">Internationalization (I18N)</a></li>
</ol>
</div>
</div>
<p>Resources are external files (that is, non-code files) that are used by
your code and compiled into your application at build time. Android
supports a number of different kinds of resource files, including XML,
PNG, and JPEG files. The XML files have very different formats depending
on what they describe. This document describes what kinds of files are
supported, and the syntax or format of each.</p>
<p>Resources are externalized from source code, and XML files are compiled into
a binary, fast loading format for efficiency reasons. Strings, likewise, are compressed
into a more efficient storage form. It is for these reasons that we have these
different resource types in the Android platform.</p>
<p>This is a fairly technically dense document, and together with the
<a href="available-resources.html">Available Resources</a>
document, they cover a lot of information about resources. It is not necessary
to know this document by heart to use Android, but rather to know that the
information is here when you need it.</p>
<a name="intro"></a>
<h2>Introduction</h2>
<p>This topic includes a terminology list associated with resources, and a series
of examples of using resources in code. For a complete guide to the supported
Android resource types, see
<a href="available-resources.html">Available Resources</a>.
</p>
<p>The Android resource system keeps track of all non-code
assets associated with an application. You use the
{@link android.content.res.Resources Resources} class to access your
application's resources; the Resources instance associated with your
application can generally be found through
{@link android.content.Context#getResources Context.getResources()}.</p>
<p>An application's resources are compiled into the application
binary at build time for you by the build system. To use a resource,
you must install it correctly in the source tree and build your
application. As part of the build process, symbols for each
of the resources are generated that you can use in your source
code -- this allows the compiler to verify that your application code matches
up with the resources you defined.</p>
<p>The rest of this section is organized as a tutorial on how to
use resources in an application.</p>
<a name="CreatingResources" id="CreatingResources"></a>
<h2>Creating Resources</h2>
<p>Android supports string, bitmap, and many other types of resource. The syntax and format
of each, and where they're stored, depends upon the type of object. In
general, though, you create resources from three types of files: XML files
(everything but bitmaps and raw), bitmap files(for images) and Raw files (anything
else, for example sound files, etc.). In fact, there are two different types of
XML file as well, those that get compiled as-is into the package, and those that
are used to generate resources by aapt. Here is a list of each
resource type, the format of the file, a description of the file, and details
of any XML files. </p>
<p>You will create and store your resource files under the appropriate
subdirectory under the <code>res/</code> directory in your project. Android
has a resource compiler (aapt) that compiles resources according to which
subfolder they are in, and the format of the file. Table 1 shows a list of the file
types for each resource. See the
<a href="available-resources.html">Available Resources</a> for
descriptions of each type of object, the syntax, and the format or syntax of
the containing file.</p>
<p class="caption">Table 1</p>
<table width="100%" border="1">
<tr>
<th scope="col">Directory</th>
<th scope="col">Resource Types </th>
</tr>
<tr>
<td><code>res/anim/</code></td>
<td>XML files that are compiled into
<a href="available-resources.html#animationdrawable">frame by
frame animation</a> or
<a href="available-resources.html#tweenedanimation">tweened
animation</a> objects </td>
</tr>
<tr>
<td><code>res/drawable/</code></td>
<td><p>.png, .9.png, .jpg files that are compiled into the following
Drawable resource subtypes:</p>
<ul class="nolist">
<li><a href="available-resources.html#imagefileresources">bitmap files</a></li>
<li><a href="available-resources.html#ninepatch">9-patches (resizable bitmaps)</a></li>
</ul>
<p>To get a resource of this type, use <code>mContext.getResources().getDrawable(R.drawable.<em>imageId</em>)</code></p>
<p class="note"><strong>Note:</strong> Image resources placed in here may
be automatically optimized with lossless image compression by the
<a href="{@docRoot}guide/developing/tools/aapt.html">aapt</a> tool. For example, a true-color PNG
that does not require more than 256 colors may be converted to an 8-bit PNG with a color palette.
This will result in an image of equal quality but which requires less memory. So be aware that the
image binaries placed in this directory can change during the build. If you plan on reading
an image as a bit stream in order to convert it to a bitmap, put your images in the
<code>res/raw/</code> folder instead, where they will not be optimized.</p>
</td>
</tr>
<tr>
<td><code>res/layout/</code></td>
<td>XML files that are compiled into screen layouts (or part of a screen).
See <a href="{@docRoot}guide/topics/ui/declaring-layout.html">Declaring Layout</a>.</td>
</tr>
<tr>
<td><code>res/values/</code></td>
<td><p>XML files that can be compiled into many kinds of resource.</p>
<p class="note"><strong>Note:</strong> Unlike the other res/ folders, this one
can hold any number of files that hold descriptions of resources to create
rather than the resources themselves. The XML element types control
where these resources are placed under the R class.</p>
<p>While the files can be named anything, these are
the typical files in this folder (the convention is to name
the file after the type of elements defined within):</p>
<ul>
<li><strong>arrays.xml</strong> to define arrays </li>
<!-- TODO: add section on arrays -->
<li><strong>colors.xml</strong> to define <a href="available-resources.html#colordrawableresources">color
drawables</a> and <a href="#colorvals">color string values</a>.
Use <code>Resources.getDrawable()</code> and
<code>Resources.getColor(), respectively,</code>
to get these resources.</li>
<li><strong>dimens.xml</strong> to define <a href="available-resources.html#dimension">dimension value</a>. Use <code>Resources.getDimension()</code> to get
these resources.</li>
<li><strong>strings.xml</strong> to define <a href="available-resources.html#stringresources">string</a> values (use either
<code>Resources.getString</code> or preferably <code>Resources.getText()</code>
to get
these resources. <code>getText()</code> will retain any rich text styling
which is usually desirable for UI strings.</li>
<li><strong>styles.xml</strong> to define <a href="available-resources.html#stylesandthemes">style</a> objects.</li>
</ul></td>
</tr>
<tr>
<td><code>res/xml/</code></td>
<td>Arbitrary XML files that are compiled and can be read at run time by
calling {@link android.content.res.Resources#getXml(int) Resources.getXML()}.</td>
</tr>
<tr>
<td><code>res/raw/</code></td>
<td>Arbitrary files to copy directly to the device. They are added uncompiled
to the compressed file that your application build produces. To use these
resources in your application, call {@link android.content.res.Resources#openRawResource(int)
Resources.openRawResource()} with the resource ID, which is R.raw.<em>somefilename</em>.</td>
</tr>
</table>
<p>Resources are compiled into the final APK file. Android creates a wrapper class,
called R, that you can use to refer to these resources in your code. R contains subclasses
named according to the path and file name of the source file</p>
<a name="colorvals" id="colorvals"></a>
<h3>Global Resource Notes</h3>
<ul>
<li>Several resources allow you to define colors. Android accepts color values
written in various web-style formats -- a hexadecimal constant in any of the
following forms: #RGB, #ARGB, #RRGGBB, #AARRGGBB. </li>
<li>All color values support setting an alpha channel value, where the first
two hexadecimal numbers specify the transparency. Zero in the alpha channel
means transparent. The default value is opaque. </li>
</ul>
<a name="UsingResources" id="UsingResources"></a>
<h2>Using Resources </h2>
<p>This section describes how to use the resources you've created. It includes the
following topics:</p>
<ul>
<li><a href="#ResourcesInCode">Using resources in code</a>&nbsp;- How to call
resources in your code to instantiate them. </li>
<li><a href="#ReferencesToResources">Referring to resources from other resources</a> &nbsp;-
You can reference resources from other resources. This lets you reuse common
resource values inside resources. </li>
<li><a href="#AlternateResources">Supporting Alternate Resources for Alternate
Configurations</a> - You can specify different resources
to load, depending on the language or display configuration of the host
hardware. </li>
</ul>
<p>At compile time, Android generates a class named R that contains resource identifiers
to all the resources in your program. This class contains several subclasses,
one for each type of resource supported by Android, and for which you provided
a resource file. Each class contains one or more identifiers for the compiled resources,
that you use in your code to load the resource. Here is a small resource file
that contains string, layout (screens or parts of screens), and image resources.</p>
<p class="note"><strong>Note:</strong> the R class is an auto-generated file and is not
designed to be edited by hand. It will be automatically re-created as needed when
the resources are updated.</p>
<pre class="prettyprint">package com.android.samples;
public final class R {
public static final class string {
public static final int greeting=0x0204000e;
public static final int start_button_text=0x02040001;
public static final int submit_button_text=0x02040008;
public static final int main_screen_title=0x0204000a;
};
public static final class layout {
public static final int start_screen=0x02070000;
public static final int new_user_pane=0x02070001;
public static final int select_user_list=0x02070002;
};
public static final class drawable {
public static final int company_logo=0x02020005;
public static final int smiling_cat=0x02020006;
public static final int yellow_fade_background=0x02020007;
public static final int stretch_button_1=0x02020008;
};
};
</pre>
<a name="ResourcesInCode" id="ResourcesInCode"></a>
<h3>Using Resources in Code </h3>
<p>Using resources in code is just a matter of knowing the full resource ID
and what type of object your resource has been compiled into. Here is the
syntax for referring to a resource:</p>
<p><code>R.<em>resource_type</em>.<em>resource_name</em></code></p>
<p>or</p>
<p><code>android.R.<em>resource_type</em>.<em>resource_name</em></code></p>
<p>Where <code>resource_type</code> is the R subclass that holds a specific type
of resource. <code>resource_name</code> is the <em>name</em> attribute for resources
defined in XML files, or the file name (without the extension) for resources
defined by other file types. Each type of resource will be added to a specific
R subclass, depending on the type of resource it is; to learn which R subclass
hosts your compiled resource type, consult the
<a href="available-resources.html">Available Resources</a> document. Resources compiled by your own application can
be referred to without a package name (simply as
<code>R.<em>resource_type</em>.<em>resource_name</em></code>). Android contains
a number of standard resources, such as screen styles and button backgrounds. To
refer to these in code, you must qualify them with <code>android</code>, as in
<code>android.R.drawable.button_background</code>.</p>
<p>Here are some good and bad examples of using compiled resources in code:</p>
<pre class="prettyprint">// Load a background for the current screen from a drawable resource.
this.getWindow().setBackgroundDrawableResource(R.drawable.my_background_image);
// WRONG Sending a string resource reference into a
// method that expects a string.
this.getWindow().setTitle(R.string.main_title);
// RIGHT Need to get the title from the Resources wrapper.
this.getWindow().setTitle(Resources.getText(R.string.main_title));
// Load a custom layout for the current screen.
setContentView(R.layout.main_screen);
// Set a slide in animation for a ViewFlipper object.
mFlipper.setInAnimation(AnimationUtils.loadAnimation(this,
R.anim.hyperspace_in));
// Set the text on a TextView object.
TextView msgTextView = (TextView)findViewByID(R.id.msg);
msgTextView.setText(R.string.hello_message); </pre>
<a name="ReferencesToResources" id="ReferencesToResources"></a>
<h3>References to Resources</h3>
<p>A value supplied in an attribute (or resource) can also be a reference to
a resource. This is often used in layout files to supply strings (so they
can be localized) and images (which exist in another file), though a reference
can be any resource type including colors and integers.</p>
<p>For example, if we have
<a href="available-resources.html#colordrawableresources">color
resources</a>, we can write a layout file that sets the text color size to be
the value contained in one of those resources:</p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText id=&quot;text&quot;
xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;fill_parent&quot; android:layout_height=&quot;fill_parent&quot;
<strong>android:textColor=&quot;&#64;color/opaque_red&quot;</strong>
android:text=&quot;Hello, World!&quot; /&gt;
</pre>
<p>Note here the use of the '@' prefix to introduce a resource reference -- the
text following that is the name of a resource in the form
of <code>@[package:]type/name</code>. In this case we didn't need to specify
the package because we are referencing a resource in our own package. To
reference a system resource, you would need to write:</p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText id=&quot;text&quot;
xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;fill_parent&quot; android:layout_height=&quot;fill_parent&quot;
android:textColor=&quot;&#64;<strong>android:</strong>color/opaque_red&quot;
android:text=&quot;Hello, World!&quot; /&gt;
</pre>
<p>As another example, you should always use resource references when supplying
strings in a layout file so that they can be localized:</p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText id=&quot;text&quot;
xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;fill_parent&quot; android:layout_height=&quot;fill_parent&quot;
android:textColor=&quot;&#64;android:color/opaque_red&quot;
android:text=&quot;&#64;string/hello_world&quot; /&gt;
</pre>
<p>This facility can also be used to create references between resources.
For example, we can create new drawable resources that are aliases for
existing images:</p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;resources&gt;
&lt;drawable id=&quot;my_background&quot;&gt;&#64;android:drawable/theme2_background&lt;/drawable&gt;
&lt;/resources&gt;
</pre>
<a name="ReferencesToThemeAttributes"></a>
<h3>References to Theme Attributes</h3>
<p>Another kind of resource value allows you to reference the value of an
attribute in the current theme. This attribute reference can <em>only</em>
be used in style resources and XML attributes; it allows you to customize the
look of UI elements by changing them to standard variations supplied by the
current theme, instead of supplying more concrete values.</p>
<p>As an example, we can use this in our layout to set the text color to
one of the standard colors defined in the base system theme:</p>
<pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;EditText id=&quot;text&quot;
xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
android:layout_width=&quot;fill_parent&quot; android:layout_height=&quot;fill_parent&quot;
<strong>android:textColor=&quot;?android:textDisabledColor&quot;</strong>
android:text=&quot;&#64;string/hello_world&quot; /&gt;
</pre>
<p>Note that this is very similar to a resource reference, except we are using
an '?' prefix instead of '@'. When you use this markup, you are supplying
the name of an attribute resource that will be looked up in the theme --
because the resource tool knows that an attribute resource is expected,
you do not need to explicitly state the type (which would be
<code>?android:attr/android:textDisabledColor</code>).</p>
<p>Other than using this resource identifier to find the value in the
theme instead of raw resources, the name syntax is identical to the '@' format:
<code>?[namespace:]type/name</code> with the type here being optional.</p>
<a name="UsingSystemResources"></a>
<h3>Using System Resources</h3>
<p>Many resources included with the system are available to applications.
All such resources are defined under the class "android.R". For example,
you can display the standard application icon in a screen with the following
code:</p>
<pre class="prettyprint">
public class MyActivity extends Activity
{
public void onStart()
{
requestScreenFeatures(FEATURE_BADGE_IMAGE);
super.onStart();
setBadgeResource(android.R.drawable.sym_def_app_icon);
}
}
</pre>
<p>In a similar way, this code will apply to your screen the standard
"green background" visual treatment defined by the system:</p>
<pre class="prettyprint">
public class MyActivity extends Activity
{
public void onStart()
{
super.onStart();
setTheme(android.R.style.Theme_Black);
}
}
</pre>
<a name="AlternateResources" id="AlternateResources"></a>
<h2>Alternate Resources (for alternate languages and configurations)</h2>
<p>You can supply different resources for your application to use depending on the UI
language or hardware configuration on the device. Note that although you can
include different string, layout, and other resources, the SDK does not expose
methods to let you specify which alternate resource set to load. Android
detects the proper set for the hardware and location, and loads them as
appropriate. Users can select alternate language settings using the settings
panel on the device. </p>
<p>To include alternate resources, create parallel resource folders with
qualifiers appended to the folder names, indicating the configuration it
applies to (language, screen orientation, and so on). For example, here is a
project that holds one string resource file for English, and another for
French:</p>
<pre>
MyApp/
res/
values-en/
strings.xml
values-fr/
strings.xml
</pre>
<p>Android supports several types of qualifiers, with various values for each.
Append these to the end of the resource folder name, separated by dashes. You
can add multiple qualifiers to each folder name, but they must appear in the
order they are listed here. For example, a folder containing drawable
resources for a fully specified configuration would look like this:</p>
<pre>
MyApp/
res/
drawable-en-rUS-large-long-port-mdpi-finger-keysexposed-qwerty-navexposed-dpad-480x320/
</pre>
<p>More typically, you will only specify a few specific configuration options. You may drop any of the values from the
complete list, as long as the remaining values are still in the same
order:</p>
<pre>
MyApp/
res/
drawable-en-rUS-finger/
drawable-port/
drawable-port-mdpi/
drawable-qwerty/
</pre>
<p>Table 2 lists the valid folder-name qualifiers, in order of precedence. Qualifiers that are listed higher in the table take precedence over those listed lower, as described in <a href="#best-match">How Android finds the best matching directory</a>. </p>
<p class="caption" id="table2">Table 2</p>
<table border="1">
<tr>
<th> Qualifier </th>
<th> Values </th>
</tr>
<tr>
<td>MCC and MNC</td>
<td><p>The mobile country code optionally followed by mobile network code
from the SIM in the device. For example
<code>mcc310</code> (U.S. on any carrier);
<code>mcc310-mnc004</code> (U.S., Verizon brand);
<code>mcc208-mnc00</code> (France, Orange brand);
<code>mcc234-mnc00</code> (U.K., BT brand).
</p><p>
If the device uses a radio connection (GSM phone), the MCC will come
from the SIM, and the MNC will come from the network to which the
device is attached. You might sometimes use the MCC alone, for example
to include country-specific legal resources in your application. If
your application specifies resources for a MCC/MNC combination, those
resources can only be used if both the MCC and the MNC match. </p></td>
</tr>
<tr>
<td>Language and region</td>
<td><p>The two letter <a href="http://www.loc.gov/standards/iso639-2/php/code_list.php">ISO
639-1</a> language code optionally followed by a two letter
<a href="http://www.iso.org/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html">ISO
3166-1-alpha-2</a> region code (preceded by lowercase &quot;r&quot;). For example
<code>fr</code>, <code>en-rUS</code>, <code>fr-rFR</code>, <code>es-rES</code>.
</p><p>
The codes are <em>not</em> case-sensitive; the r prefix is used to
distinguish the region portion.
You cannot specify a region alone, but you can specify a language alone,
for example <code>en</code>, <code>fr</code>, <code>es</code>.</p> </td>
</tr>
<tr>
<td>Screen dimensions</td>
<td><p><code>small</code>, <code>normal</code>, <code>large</code>
</p><p>
Specify that the resource is for a particular class of screen.
The meanings of these are:</p>
<ul>
<li> <b>Normal screens</b> are based on the traditional Android HVGA
medium density screen. A screen is considered to be normal if it is
at least this size (independent of density) and not large. Examples
of such screens a WQVGA low density, HVGA medium density, WVGA
high density.
<li> <b>Small screens</b> are based on the space available on a
QVGA low density screen. Considering a portrait HVGA display, this has
the same available width but less height -- it is 3:4 vs. HVGA's
2:3 aspect ratio. Examples are QVGA low density and VGA high
density.
<li> <b>Large screens</b> are based on the space available on a
VGA medium density screen. Such a screen has significantly more
available space in both width and height than an HVGA display.
Examples are VGA and WVGA medium density screens.
</td>
</tr>
<tr>
<td>Wider/taller screens</td>
<td><p><code>long</code>, <code>notlong</code>
</p><p>
Specify that the resource is for a taller/wider than traditional
screen. This is based purely on the aspect ration of the screen:
QVGA, HVGA, and VGA are notlong; WQVGA, WVGA, FWVGA are long. Note
that long may mean either wide or tall, depending on the current
orientation.</p>
</td>
</tr>
<tr>
<td>Screen orientation</td>
<td><p><code>port</code>, <code>land</code>, <code>square</code>
</p><p>
Specifies that the resource is for a screen that is tall (port)
or wide (land); square is not currently used.</p>
</td>
</tr>
<tr>
<td>Screen pixel density</td>
<td><p><code>ldpi</code>, <code>mdpi</code>, <code>hdpi</code>, <code>nodpi</code>
</p><p>
Specifies the screen density the resource is defined for. The medium
density of traditional HVGA screens (mdpi) is defined to be approximately
160dpi; low density (ldpi) is 120, and high density (hdpi) is 240. There
is thus a 4:3 scaling factor between each density, so a 9x9 bitmap
in ldpi would be 12x12 is mdpi and 16x16 in hdpi. The special
<code>nodpi</code> density can be used with bitmap resources to prevent
them from being scaled at load time to match the device density.
</p><p>
When Android selects which resource files to use,
it handles screen density differently than the other qualifiers.
In step 1 of <a href="#best-match">How Android finds the best
matching directory</a> (below), screen density is always considered to
be a match. In step 4, if the qualifier being considered is screen
density, Android will select the best final match at that point,
without any need to move on to step 5.
</p><p>
You can also specify explicit densities like <code>92dpi</code>
or <code>108dpi</code>, but these are not fully supported by the
system so should not be used.
</p>
</td>
</tr>
<tr>
<td>Touchscreen type</td>
<td><code>notouch</code>, <code>stylus</code>, <code>finger</code></td>
</tr>
<tr>
<td>Whether the keyboard is available to the user</td>
<td><p><code>keysexposed</code>, <code>keyshidden</code>, <code>keyssoft</code>
</p><p>
If your application has specific resources that should only be used with a soft keyboard, use the <code>keyssoft</code> value. If no <code>keyssoft</code> resources are available (only <code>keysexposed</code> and <code>keyshidden</code>) and the device shows a soft keyboard, the system will use <code>keysexposed</code> resources.</p> </td>
</tr>
<tr>
<td>Primary text input method</td>
<td><code>nokeys</code>, <code>qwerty</code>, <code>12key</code> </td>
</tr>
<tr>
<td>Whether the navigation keys are available to the user</td>
<td><p><code>navexposed</code>, <code>navhidden</code>
</p><p>
If the hardware's navigation keys are currently available to
the user, the navexposed resources will be used; if they are not
available (such as behind a closed lid), navhidden will be used.</p></td>
</tr>
<tr>
<td>Primary non-touchscreen<br />
navigation method</td>
<td><code>nonav</code>, <code>dpad</code>, <code>trackball</code>, <code>wheel</code> </td>
</tr>
<tr>
<td>Screen dimensions</td>
<td><code>320x240</code>, <code>640x480</code>, etc. The larger dimension
must be specified first. This configuration is deprecated and
should not be used; use instead screen dimension, wider/taller
screens, and screen orientation described above.</td>
</tr>
<tr>
<td>SDK version</td>
<td>The SDK version supported by the device, for example <code>v3</code>. The Android 1.0 SDK is <code>v1, </code> the 1.1 SDK is <code>v2</code>, and the 1.5 SDK is <code>v3</code>.</td>
</tr>
<tr>
<td>(Minor version)</td>
<td>(You cannot currently specify minor version. It is always set to 0.)</td>
</tr>
</table>
<p>This list does not include device-specific parameters such as carrier,
branding, device/hardware, or manufacturer. Everything that an application
needs to know about the device that it is running on is encoded via the
resource qualifiers in the table above.</p>
<p>All resource directories, qualified and unqualified, live under the <code>res/</code> folder. Here are some guidelines on qualified resource directory names:</p>
<ul>
<li>You can specify multiple qualifiers, separated by dashes. For example, <code>drawable-en-rUS-land</code> will apply to US-English
devices in landscape orientation. </li>
<li>The qualifiers must be in the order listed in <a href="#table2">Table 2</a> above. For example:
<ul>
<li>Correct: <code>values-mcc460-nokeys/</code></li>
<li>Incorrect: <code>values-nokeys-mcc460/</code></li>
</ul>
</li>
<li>Values are case-insensitive. The resource compiler converts folder names
to lower case before processing to avoid problems in case-insensitive
file systems. On case-sensitive file systems, you should keep all names
lower-case or at least use a consistent case to protect your future
sanity when trying to find a resource file.</li>
<li>Only one value for each qualifier type is supported. For example, if you want to use exactly the same drawable files for Spain and France, you will need two resource directories, such as <code>drawable-rES/</code> and <code>drawable-rFR/</code>, containing identical files. You cannot
have a directory named <code>drawable-rES-rFR/</code>. </li>
<li>Qualified directories cannot be nested. For example, you cannot have <code>res/drawable/drawable-en</code>. </li>
</ul>
<h3>How resources are referenced in code</h3>
<p>All resources will be referenced in code or resource reference syntax by
their simple, undecorated names. So if a resource were named this:<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<code>MyApp/res/drawable-port-mdpi/myimage.png</code><br />
It would be referenced as this:<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<code>R.drawable.myimage</code> (code)<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<code>&#064;drawable/myimage</code> (XML)</p>
<p>If several drawable directories are available, Android will select one of them (as described below) and load <code>myimage.png</code> from it.</p>
<h3 id="best-match">How Android finds the best matching directory </h3>
<p>Android will pick which of the various underlying resource files should be
used at runtime, depending on the current configuration of the device.
The example used here assumes the following device configuration:</p>
<blockquote>
<p>Locale = <code>en-GB</code><br>
Screen orientation = <code>port</code><br>
Screen pixel density = <code>mdpi</code><br>
Touchscreen type = <code>notouch</code><br>
Primary text input method = <code>12key</code><br>
</p>
</blockquote>
<p>Here is how Android makes the selection: </p>
<ol>
<li>
Eliminate resource files that contradict the
device configuration. For example, assume that the following resource directories are available for drawables. The <code>drawable-fr-rCA/</code> directory will be eliminated, because it contradicts the locale of the device.<br>
<pre>MyApp/res/drawable/
MyApp/res/drawable-en/
<strike>MyApp/res/drawable-fr-rCA/</strike>
MyApp/res/drawable-en-port/
MyApp/res/drawable-en-notouch-12key/
MyApp/res/drawable-port-ldpi/
MyApp/res/drawable-port-notouch-12key</pre>
<strong>Exception: </strong>Screen pixel density is the one qualifier that is not used to eliminate files. Even though the screen density of the device is medium dpi, <code>drawable-port-ldpi/</code> is not eliminated from the list, because every screen density is considered to be a
match at this point.</li>
<li>From <a href="#table2">Table 2</a>, pick the highest-precedence qualifier that remains in the list. (Start with MCC, then move down through the list.) </li>
<li>Do any of the available resource directories include this qualifier? </li>
<ul>
<li>If No, return to step 2 and look at the next qualifier listed in Table 2. In our example, the answer is &quot;no&quot; until we reach Language.</li>
<li>If Yes, move on to step 4.</li>
</ul>
<li>Eliminate resource directories that do not include this qualifier. In our example, we eliminate all the directories that do not include a language qualifier. </li>
<pre><strike>MyApp/res/drawable/</strike>
MyApp/res/drawable-en/
MyApp/res/drawable-en-port/
MyApp/res/drawable-en-notouch-12key/
<strike>MyApp/res/drawable-port-ldpi/</strike>
<strike>MyApp/res/drawable-port-notouch-12key</strike></pre>
<strong>Exception:</strong> If the qualifier in question is screen pixel density, Android will select the option that most closely matches the device, and the selection process will be complete. In general, Android will prefer scaling down a larger original image to scaling up a smaller original image.<br><br></li>
<li>Go back and repeat steps 2, 3, and 4 until only one choice remains. In the example, screen orientation is the next qualifier in the table for which we have any matches.
Eliminate resources that do not specify a screen orientation. </p>
<pre><strike>MyApp/res/drawable-en/</strike>
MyApp/res/drawable-en-port/
<strike>MyApp/res/drawable-en-notouch-12key/</strike></pre>
Only one choice remains, so that's it. When drawables are called for in this
example application, the Android system will load resources from the
<code>MyApp/res/drawable-en-port/</code> directory. In addition, if the
resource being loaded is a bitmap, it will be scaled up so that its supplied
low density matches the device's medium density.
</ol>
<p class="note"><strong>Tip:</strong> The <em>precedence</em> of the qualifiers is more important than the number of qualifiers that exactly match the device. For example, in step 4 above, the last choice on the list includes three qualifiers that exactly match the device (orientation, touchscreen type, and input method), while <code>drawable-en</code> has only one parameter that matches (language). However, language has a higher precedence, so <code>drawable-port-notouch-12key</code> is out.</p>
<p>This flowchart summarizes how Android selects resource directories to load.</p>
<p><img src="../../../images/resources/res-selection-flowchart.png" alt="resource-selection" width="461" height="471" style="margin:15px"></p>
<h3>Terminology</h3>
<p>The resource system brings a number of different pieces together to
form the final complete resource functionality. To help understand the
overall system, here are some brief definitions of the core concepts and
components you will encounter in using it:</p>
<p><strong>Asset</strong>: A single blob of data associated with an application. This
includes object files compiled from the Java source code, graphics (such as PNG
images), XML files, etc. These files are organized in a directory hierarchy
that, during final packaging of the application, is bundled together into a
single ZIP file.</p>
<p><strong>aapt</strong>: Android Asset Packaging Tool. The tool that generates the
final ZIP file of application assets. In addition to collecting raw assets
together, it also parses resource definitions into binary asset data.</p>
<p><strong>Resource Table</strong>: A special asset that aapt generates for you,
describing all of the resources contained in an application/package.
This file is accessed for you by the Resources class; it is not touched
directly by applications.</p>
<p><strong>Resource</strong>: An entry in the Resource Table describing a single
named value. Broadly, there are two types of resources: primitives and
bags.</p>
<p><strong>Resource Identifier</strong>: In the Resource Table all resources are
identified by a unique integer number. In source code (resource descriptions,
XML files, Java source code) you can use symbolic names that stand as constants for
the actual resource identifier integer.</p>
<p><strong>Primitive Resource</strong>: All primitive resources can be written as a
simple string, using formatting to describe a variety of primitive types
included in the resource system: integers, colors, strings, references to
other resources, etc. Complex resources, such as bitmaps and XML
describes, are stored as a primitive string resource whose value is the path
of the underlying Asset holding its actual data.</p>
<p><strong>Bag Resource</strong>: A special kind of resource entry that, instead of a
simple string, holds an arbitrary list of name/value pairs. Each name is
itself a resource identifier, and each value can hold
the same kinds of string formatted data as a normal resource. Bags also
support inheritance: a bag can inherit the values from another bag, selectively
replacing or extending them to generate its own contents.</p>
<p><strong>Kind</strong>: The resource kind is a way to organize resource identifiers
for various purposes. For example, drawable resources are used to
instantiate Drawable objects, so their data is a primitive resource containing
either a color constant or string path to a bitmap or XML asset. Other
common resource kinds are string (localized string primitives), color
(color primitives), layout (a string path to an XML asset describing a view
layout), and style (a bag resource describing user interface attributes).
There is also a standard "attr" resource kind, which defines the resource
identifiers to be used for naming bag items and XML attributes</p>
<p><strong>Style</strong>: The name of the resource kind containing bags that are used
to supply a set of user interface attributes. For example, a TextView class may
be given a style resource that defines its text size, color, and alignment.
In a layout XML file, you associate a style with a bag using the "style"
attribute, whose value is the name of the style resource.</p>
<p><strong>Style Class</strong>: Specifies a related set of attribute resources.
This data is not placed in the resource table itself, but used to generate
constants in the source code that make it easier for you to retrieve values out of
a style resource and/or XML tag's attributes. For example, the
Android platform defines a "View" style class that
contains all of the standard view attributes: padding, visibility,
background, etc.; when View is inflated it uses this style class to
retrieve those values from the XML file (at which point style and theme
information is applied as approriate) and load them into its instance.</p>
<p><strong>Configuration</strong>: For any particular resource identifier, there may be
multiple different available values depending on the current configuration.
The configuration includes the locale (language and country), screen
orientation, etc. The current configuration is used to
select which resource values are in effect when the resource table is
loaded.</p>
<p><strong>Theme</strong>: A standard style resource that supplies global
attribute values for a particular context. For example, when writing an
Activity the application developer can select a standard theme to use, such
as the Theme.White or Theme.Black styles; this style supplies information
such as the screen background image/color, default text color, button style,
text editor style, text size, etc. When inflating a layout resource, most
values for widgets (the text color, selector, background) if not explicitly
set will come from the current theme; style and attribute
values supplied in the layout can also assign their value from explicitly
named values in the theme attributes if desired.</p>
<p><strong>Overlay</strong>: A resource table that does not define a new set of resources,
but instead replaces the values of resources that are in another resource table.
Like a configuration, this is applied at load time
to the resource data; it can add new configuration values (for example
strings in a new locale), replace existing values (for example change
the standard white background image to a "Hello Kitty" background image),
and modify resource bags (for example change the font size of the Theme.White
style to have an 18 pt font size). This is the facility that allows the
user to select between different global appearances of their device, or
download files with new appearances.</p>
<h2>Resource Reference</h2>
<p>The <a href="available-resources.html">Available Resources</a>
document provides a detailed list of the various types of resource and how to use them
from within the Java source code, or from other references.</p>
<a name="i18n" id="i18n"></a>
<h2>Internationalization and Localization</h2>
<p class="note"><strong>Coming Soon:</strong> Internationalization and Localization are
critical, but are also not quite ready yet in the current SDK. As the
SDK matures, this section will contain information on the Internationalization
and Localization features of the Android platform. In the meantime, it is a good
idea to start by externalizing all strings, and practicing good structure in
creating and using resources.</p>