original

[gb-231r1-is01/Gingerbread_2.3.3_r1_IS01.git] / frameworks / base / docs / html / guide / topics / resources / providing-resources.jd

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

<div id="qv-wrapper">
<div id="qv">
  <h2>Quickview</h2>
  <ul>
    <li>Different types of resources belong in different subdirectories of {@code res/}</li>
    <li>Alternative resources provide configuration-specific resource files</li>
    <li>Always include default resources so your app does not depend on specific
device configurations</li>
  </ul>
  <h2>In this document</h2>
  <ol>
    <li><a href="#ResourceTypes">Grouping Resource Types</a></li>
    <li><a href="#AlternativeResources">Providing Alternative Resources</a>
      <ol>
        <li><a href="#QualifierRules">Qualifier name rules</a></li>
        <li><a href="#AliasResources">Creating alias resources</a></li>
      </ol>
    </li>
    <li><a href="#Compatibility">Providing the Best Device Compatibility with Resources</a>
      <ol>
        <li><a href="#ScreenCompatibility">Providing screen resource compatibility for Android
1.5</a></li>
      </ol>
    </li>
    <li><a href="#BestMatch">How Android Finds the Best-matching Resource</a></li>
    <li><a href="#KnownIssues">Known Issues</a></li>
  </ol>

  <h2>See also</h2>
  <ol>
    <li><a href="accessing-resources.html">Accessing Resources</a></li>
    <li><a href="available-resources.html">Resource Types</a></li>
    <li><a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
Screens</a></li>
  </ol>
</div>
</div>

<p>You should always externalize application resources such as images and strings from your
code, so that you can maintain them independently. You should also provide alternative resources for
specific device configurations, by grouping them in specially-named resource directories. At
runtime, Android uses uses the appropriate resource based on the current configuration. For
example, you might want to provide a different UI layout depending on the screen size or different
strings depending on the language setting.</p>

<p>Once you externalize your application resources, you can access them
using resource IDs that are generated in your project's {@code R} class. How to use
resources in your application is discussed in <a href="accessing-resources.html">Accessing
Resources</a>. This document shows you how to group your resources in your Android project and
provide alternative resources for specific device configurations.</p>


<h2 id="ResourceTypes">Grouping Resource Types</h2>

<p>You should place each type of resource in a specific subdirectory of your project's
{@code res/} directory. For example, here's the file hierarchy for a simple project:</p>

<pre class="classic no-pretty-print">
MyProject/
    src/  <span style="color:black">
        MyActivity.java  </span>
    res/
        drawable/  <span style="color:black">
            icon.png  </span>
        layout/  <span style="color:black">
            main.xml
            info.xml</span>
        values/  <span style="color:black">
            strings.xml  </span>
</pre>

<p>As you can see in this example, the {@code res/} directory contains all the resources (in
subdirectories): an image resource, two layout resources, and a string resource file. The resource
directory names are important and are described in table 1.</p>

<p class="table-caption" id="table1"><strong>Table 1.</strong> Resource directories
supported inside project {@code res/} directory.</p>

<table>
  <tr>
    <th scope="col">Directory</th>
    <th scope="col">Resource Type</th>
  </tr>

  <tr>
    <td><code>anim/</code></td>
    <td>XML files that define tween animations. See <a
href="animation-resource.html">Animation Resources</a>.</td>
  </tr>

  <tr>
    <td><code>color/</code></td>
    <td>XML files that define a state list of colors. See <a href="color-list-resource.html">Color
State List Resource</a></td>
  </tr>

  <tr>
    <td><code>drawable/</code></td>
    <td><p>Bitmap files ({@code .png}, {@code .9.png}, {@code .jpg}, {@code .gif}) or XML files that
are compiled into the following drawable resource subtypes:</p>
      <ul>
        <li>Bitmap files</li>
        <li>Nine-Patches (re-sizable bitmaps)</li>
        <li>State lists</li>
        <li>Shapes</li>
        <li>Animation drawables</li>
        <li>Other drawables</li>
      </ul>
      <p>See <a href="drawable-resource.html">Drawable Resources</a>.</p>
    </td>
  </tr>

  <tr>
    <td><code>layout/</code></td>
    <td>XML files that define a user interface layout.
        See <a href="layout-resource.html">Layout Resource</a>.</td>
  </tr>

  <tr>
    <td><code>menu/</code></td>
    <td>XML files that define application menus, such as an Options Menu, Context Menu, or Sub
Menu. See <a href="menu-resource.html">Menu Resource</a>.</td>
  </tr>

  <tr>
    <td><code>raw/</code></td>
    <td><p>Arbitrary files to save in their raw form. To open these resources with a raw
{@link java.io.InputStream}, call {@link android.content.res.Resources#openRawResource(int)
Resources.openRawResource()} with the resource ID, which is {@code R.raw.<em>filename</em>}.</p>
      <p>However, if you need access to original file names and file hierarchy, you might consider
saving some resources in the {@code
assets/} directory (instead of {@code res/raw/}). Files in {@code assets/} are not given a
resource ID, so you can read them only using {@link android.content.res.AssetManager}.</p></td>
  </tr>

  <tr>
    <td><code>values/</code></td>
    <td><p>XML files that contain simple values, such as strings, integers, and colors.</p>
      <p>Whereas XML resource files in other {@code res/} subdirectories define a single resource
based on the XML filename, files in the {@code values/} directory describe multiple resources.
For a file in this directory, each child of the {@code &lt;resources&gt;} element defines a single
resource. For example, a {@code &lt;string&gt;} element creates an
{@code R.string} resource and a  {@code &lt;color&gt;} element creates an {@code R.color}
resource.</p>
      <p>Because each resource is defined with its own XML element, you can name the file
whatever you want and place different resource types in one file. However, for clarity, you might
want to place unique resource types in different files. For example, here are some filename
conventions for resources you can create in this directory:</p>
      <ul>
        <li>arrays.xml for resource arrays (<a
href="more-resources.html#TypedArray">typed arrays</a>).</li>
        <li>colors.xml for <a
href="more-resources.html#Color">color values</a></li>
        <li>dimens.xml for <a
href="more-resources.html#Dimension">dimension values</a>.</li>
        <li>strings.xml for <a href="string-resource.html">string
values</a>.</li>
        <li>styles.xml for <a href="style-resource.html">styles</a>.</li>
      </ul>
      <p>See <a href="string-resource.html">String Resources</a>,
        <a href="style-resource.html">Style Resource</a>, and
        <a href="more-resources.html">More Resource Types</a>.</p>
    </td>
  </tr>

  <tr>
    <td><code>xml/</code></td>
    <td>Arbitrary XML files that can be read at runtime by calling {@link
android.content.res.Resources#getXml(int) Resources.getXML()}. Various XML configuration files
must be saved here, such as a <a
href="{@docRoot}guide/topics/search/searchable-config.html">searchable configuration</a>.
<!-- or preferences configuration. --></td>
  </tr>
</table>

<p class="caution"><strong>Caution:</strong> Never save resource files directly inside the
{@code res/} directory&mdash;it will cause a compiler error.</p>

<p>For more information about certain types of resources, see the <a
href="available-resources.html">Resource Types</a> documentation.</p>

<p>The resources that you save in the subdirectories defined in table 1 are your "default"
resources. That is, these resources define the default design and content for your application.
However, different types of Android-powered devices might call for different types of resources.
For example, if a device has a larger than normal screen, then you should provide
different layout resources that take advantage of the extra screen space. Or, if a device has a
different language setting, then you should provide different string resources that translate the
text in your user interface. To provide these different resources for different device
configurations, you need to provide alternative resources, in addition to your default
resources.</p>


<h2 id="AlternativeResources">Providing Alternative Resources</h2>


<div class="figure" style="width:421px">
<img src="{@docRoot}images/resources/resource_devices_diagram2.png" height="137" alt="" />
<p class="img-caption">
<strong>Figure 1.</strong> Two different devices, one using alternative resources.</p>
</div>

<p>Almost every application should provide alternative resources to support specific device
configurations. For instance, you should include alternative drawable resources for different
screen densities and alternative string resources for different languages. At runtime, Android
detects the current device configuration and loads the appropriate
resources for your application.</p>

<p>To specify configuration-specific alternatives for a set of resources:</p>
<ol>
  <li>Create a new directory in {@code res/} named in the form {@code
<em>&lt;resources_name&gt;</em>-<em>&lt;config_qualifier&gt;</em>}.
    <ul>
      <li><em>{@code &lt;resources_name&gt;}</em> is the directory name of the corresponding default
resources (defined in table 1).</li>
      <li><em>{@code &lt;qualifier&gt;}</em> is a name that specifies an individual configuration
for which these resources are to be used (defined in table 2).</li>
    </ul>
    <p>You can append more than one <em>{@code &lt;qualifier&gt;}</em>. Separate each
one with a dash.</p>
  </li>
  <li>Save the respective alternative resources in this new directory. The resource files must be
named exactly the same as the default resource files.</li>
</ol>

<p>For example, here are some default and alternative resources:</p>

<pre class="classic no-pretty-print">
res/
    drawable/   <span style="color:black">
        icon.png
        background.png    </span>
    drawable-hdpi/  <span style="color:black">
        icon.png
        background.png  </span>
</pre>

<p>The {@code hdpi} qualifier indicates that the resources in that directory are for devices with a
high-density screen. The images in each of these drawable directories are sized for a specific
screen density, but the filenames are exactly
the same. This way, the resource ID that you use to reference the {@code icon.png} or {@code
background.png} image is always the same, but Android selects the
version of each resource that best matches the current device, by comparing the device
configuration information with the qualifiers in the alternative resource directory name.</p>

<p>Android supports several configuration qualifiers and you can
add multiple qualifiers to one directory name, by separating each qualifier with a dash. Table 2
lists the valid configuration qualifiers, in order of precedence&mdash;if you use multiple
qualifiers for one resource directory, they must be added to the directory name in the order they
are listed in the table.</p>

<p class="note"><strong>Note:</strong> Some configuration qualifiers were added after Android 1.0,
so not
all versions of Android support all the qualifiers listed in table 2. New qualifiers
indicate the version in which they were added. To avoid any issues, always include a set of default
resources for resources that your application uses. For more information, see the section about <a
href="#Compatibility">Providing the Best Device Compatibility with Resources</a>.</p>

<p class="table-caption" id="table2"><strong>Table 2.</strong> Configuration qualifier
names.</p>
<table>
    <tr>
        <th>Qualifier</th>
        <th>Values</th>
        <th>Description</th>
    </tr>
    <tr id="MccQualifier">
      <td>MCC and MNC</td>
      <td>Examples:<br/>
        <code>mcc310</code><br/>
        <code><nobr>mcc310-mnc004</nobr></code><br/>
        <code>mcc208-mnc00</code><br/>
        etc.
      </td>
      <td>
        <p>The mobile country code (MCC), optionally followed by mobile network code (MNC)
        from the SIM card in the device. For example, <code>mcc310</code> is U.S. on any carrier,
        <code>mcc310-mnc004</code> is U.S. on Verizon, and <code>mcc208-mnc00</code> is France on
        Orange.</p>
        <p>If the device uses a radio connection (GSM phone), the MCC comes
        from the SIM, and the MNC comes from the network to which the
        device is connected.</p>
        <p>You can also use the MCC alone (for example, to include country-specific legal
resources in your application). If you need to specify based on the language only, then use the
<em>language and region</em> qualifier instead (discussed next). If you decide to use the MCC and
MNC qualifier, you should do so with care and test that it works as expected.</p>
        <p>Also see the configuration fields {@link
android.content.res.Configuration#mcc}, and {@link
android.content.res.Configuration#mnc}, which indicate the current mobile country code
and mobile network code, respectively.</p>
      </td>
    </tr>
    <tr id="LocaleQualifier">
      <td>Language and region</td>
      <td>Examples:<br/>
        <code>en</code><br/>
        <code>fr</code><br/>
        <code>en-rUS</code><br/>
        <code>fr-rFR</code><br/>
        <code>fr-rCA</code><br/>
        etc.
      </td>
      <td><p>The language is defined by a 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;{@code r}&quot;).
        </p><p>
        The codes are <em>not</em> case-sensitive; the {@code r} prefix is used to
        distinguish the region portion.
        You cannot specify a region alone.</p>
        <p>This can change during the life
of your application if the user changes his or her language in the system settings. See <a
href="runtime-changes.html">Handling Runtime Changes</a> for information about
how this can affect your application during runtime.</p>
        <p>See <a href="localization.html">Localization</a> for a complete guide to localizing
your application for other languages.</p>
        <p>Also see the {@link android.content.res.Configuration#locale} configuration field, which
indicates the current locale.</p>
      </td>
    </tr>
    <tr id="ScreenSizeQualifier">
      <td>Screen size</td>
      <td>
        <code>small</code><br/>
        <code>normal</code><br/>
        <code>large</code><br/>
        <code>xlarge</code>
      </td>
      <td>
        <ul class="nolist">
        <li>{@code small}: Screens based on the space available on a
        low-density QVGA screen.  Considering a portrait HVGA display, this has
        the same available width but less height&mdash;it is 3:4 vs. HVGA's
        2:3 aspect ratio.  Examples are QVGA low density and VGA high
        density.</li>
        <li>{@code normal}: Screens based on the traditional
        medium-density HVGA screen.  A screen is considered to be normal if it is
        at least this size (independent of density) and not larger.  Examples
        of such screens a WQVGA low density, HVGA medium density, WVGA
        high density.</li>
        <li>{@code large}: Screens based on the space available on a
        medium-density VGA 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.</li>
        <li>{@code xlarge}: Screens that are considerably larger than the traditional
        medium-density HVGA screen. In most cases, devices with extra large screens would be too
large to carry in a pocket and would most likely be tablet-style devices. <em>Added in API Level
9.</em></li>
        </ul>
        <p><em>Added in API Level 4.</em></p>
        <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
Screens</a> for more information.</p>
        <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field,
which indicates whether the screen is small, normal,
or large.</p>
      </td>
    </tr>
    <tr id="ScreenAspectQualifier">
      <td>Screen aspect</td>
      <td>
        <code>long</code><br/>
        <code>notlong</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code long}: Long screens, such as WQVGA, WVGA, FWVGA</li>
          <li>{@code notlong}: Not long screens, such as QVGA, HVGA, and VGA</li>
        </ul>
        <p><em>Added in API Level 4.</em></p>
        <p>This is based purely on the aspect ratio of the screen (a "long" screen is wider). This
is not related to the screen orientation.</p>
        <p>Also see the {@link android.content.res.Configuration#screenLayout} configuration field,
which indicates whether the screen is long.</p>
      </td>
    </tr>
    <tr id="OrientationQualifier">
      <td>Screen orientation</td>
      <td>
        <code>port</code><br/>
        <code>land</code>  <!-- <br/>
        <code>square</code>  -->
      </td>
      <td>
        <ul class="nolist">
          <li>{@code port}: Device is in portrait orientation (vertical)</li>
          <li>{@code land}: Device is in landscape orientation (horizontal)</li>
          <!-- Square mode is currently not used. -->
        </ul>
        <p>This can change during the life of your application if the user rotates the
screen. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about
how this affects your application during runtime.</p>
        <p>Also see the {@link android.content.res.Configuration#orientation} configuration field,
which indicates the current device orientation.</p>
      </td>
    </tr>
    <tr id="DockQualifier">
      <td>Dock mode</td>
      <td>
        <code>car</code><br/>
        <code>desk</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code car}: Device is in a car dock</li>
          <li>{@code desk}: Device is in a desk dock</li>
        </ul>
        <p><em>Added in API Level 8.</em></p>
        <p>This can change during the life of your application if the user places the device in a
dock. You can enable or disable this mode using {@link
android.app.UiModeManager}. See <a href="runtime-changes.html">Handling Runtime Changes</a> for
information about how this affects your application during runtime.</p>
      </td>
    </tr>
    <tr id="NightQualifier">
      <td>Night mode</td>
      <td>
        <code>night</code><br/>
        <code>notnight</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code night}: Night time</li>
          <li>{@code notnight}: Day time</li>
        </ul>
        <p><em>Added in API Level 8.</em></p>
        <p>This can change during the life of your application if night mode is left in
auto mode (default), in which case the mode changes based on the time of day.  You can enable
or disable this mode using {@link android.app.UiModeManager}. See <a
href="runtime-changes.html">Handling Runtime Changes</a> for information about how this affects your
application during runtime.</p>
      </td>
    </tr>
    <tr id="DensityQualifier">
      <td>Screen pixel density (dpi)</td>
      <td>
        <code>ldpi</code><br/>
        <code>mdpi</code><br/>
        <code>hdpi</code><br/>
        <code>xhdpi</code><br/>
        <code>nodpi</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code ldpi}: Low-density screens; approximately 120dpi.</li>
          <li>{@code mdpi}: Medium-density (on traditional HVGA) screens; approximately
160dpi.</li>
          <li>{@code hdpi}: High-density screens; approximately 240dpi.</li>
          <li>{@code xhdpi}: Extra high-density screens; approximately 320dpi. <em>Added in API
Level 8</em></li>
          <li>{@code nodpi}: This can be used for bitmap resources that you do not want to be scaled
to match the device density.</li>
        </ul>
        <p><em>Added in API Level 4.</em></p>
        <p>There is thus a 3:4:6 scaling ratio between the three densities, so a 9x9 bitmap
         in ldpi is 12x12 in mdpi and 18x18 in hdpi.</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="#BestMatch">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 selects the best final match at that point,
         without any need to move on to step 5.
         </p>
        <p>See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
Screens</a> for more information about how to handle screen sizes and how Android might scale
your bitmaps.</p>
       </td>
    </tr>
    <tr id="TouchscreenQualifier">
      <td>Touchscreen type</td>
      <td>
        <code>notouch</code><br/>
        <code>stylus</code><br/>
        <code>finger</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code notouch}: Device does not have a touchscreen.</li>
          <li>{@code stylus}: Device has a resistive touchscreen that's suited for use with a
stylus.</li>
          <li>{@code finger}: Device has a touchscreen.</li>
        </ul>
        <p>Also see the {@link android.content.res.Configuration#touchscreen} configuration field,
which indicates the type of touchscreen on the device.</p>
      </td>
    </tr>
    <tr id="KeyboardAvailQualifier">
      <td>Keyboard availability</td>
      <td>
        <code>keysexposed</code><br/>
        <code>keyssoft</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code keysexposed}: Device has a keyboard available. If the device has a
software keyboard enabled (which is likely), this may be used even when the hardware keyboard is
<em>not</em> exposed to the user, even if the device has no hardware keyboard. If no software
keyboard is provided or it's disabled, then this is only used when a hardware keyboard is
exposed.</li>
          <li>{@code keyshidden}: Device has a hardware keyboard available but it is
hidden <em>and</em> the device does <em>not</em> have a software keyboard enabled.</li>
          <li>{@code keyssoft}: Device has a software keyboard enabled, whether it's
visible or not.</li>
        </ul>
        <p>If you provide <code>keysexposed</code> resources, but not <code>keyssoft</code>
resources, the system uses the <code>keysexposed</code> resources regardless of whether a
keyboard is visible, as long as the system has a software keyboard enabled.</p>
        <p>This can change during the life of your application if the user opens a hardware
keyboard. See <a href="runtime-changes.html">Handling Runtime Changes</a> for information about how
this affects your application during runtime.</p>
        <p>Also see the configuration fields {@link
android.content.res.Configuration#hardKeyboardHidden} and {@link
android.content.res.Configuration#keyboardHidden}, which indicate the visibility of a hardware
keyboard and and the visibility of any kind of keyboard (including software), respectively.</p>
      </td>
    </tr>
    <tr id="ImeQualifier">
      <td>Primary text input method</td>
      <td>
        <code>nokeys</code><br/>
        <code>qwerty</code><br/>
        <code>12key</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code nokeys}: Device has no hardware keys for text input.</li>
          <li>{@code qwerty}: Device has a hardware qwerty keyboard, whether it's visible to the
user
or not.</li>
          <li>{@code 12key}: Device has a hardware 12-key keyboard, whether it's visible to the user
or not.</li>
        </ul>
        <p>Also see the {@link android.content.res.Configuration#keyboard} configuration field,
which indicates the primary text input method available.</p>
      </td>
    </tr>
    <tr id="NavAvailQualifier">
      <td>Navigation key availability</td>
      <td>
        <code>navexposed</code><br/>
        <code>navhidden</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code navexposed}: Navigation keys are available to the user.</li>
          <li>{@code navhidden}: Navigation keys are not available (such as behind a closed
lid).</li>
        </ul>
        <p>This can change during the life of your application if the user reveals the navigation
keys. See <a href="runtime-changes.html">Handling Runtime Changes</a> for
information about how this affects your application during runtime.</p>
        <p>Also see the {@link android.content.res.Configuration#navigationHidden} configuration
field, which indicates whether navigation keys are hidden.</p>
      </td>
    </tr>
    <tr id="TouchQualifier">
      <td>Primary non-touch navigation method</td>
      <td>
        <code>nonav</code><br/>
        <code>dpad</code><br/>
        <code>trackball</code><br/>
        <code>wheel</code>
      </td>
      <td>
        <ul class="nolist">
          <li>{@code nonav}: Device has no navigation facility other than using the
touchscreen.</li>
          <li>{@code dpad}: Device has a directional-pad (d-pad) for navigation.</li>
          <li>{@code trackball}: Device has a trackball for navigation.</li>
          <li>{@code wheel}: Device has a directional wheel(s) for navigation (uncommon).</li>
        </ul>
        <p>Also see the {@link android.content.res.Configuration#navigation} configuration field,
which indicates the type of navigation method available.</p>
      </td>
    </tr>
<!-- DEPRECATED
    <tr>
      <td>Screen dimensions</td>
      <td>Examples:<br/>
        <code>320x240</code><br/>
        <code>640x480</code><br/>
        etc.
      </td>
      <td>
        <p>The larger dimension must be specified first. <strong>This configuration is deprecated
and should not be used</strong>. Instead use "screen size," "wider/taller screens," and "screen
orientation" described above.</p>
      </td>
    </tr>
-->
    <tr id="VersionQualifier">
      <td>System Version (API Level)</td>
      <td>Examples:<br/>
        <code>v3</code><br/>
        <code>v4</code><br/>
        <code>v7</code><br/>
        etc.</td>
      <td>
        <p>The API Level supported by the device. For example, <code>v1</code> for API Level
1 (devices with Android 1.0 or higher) and <code>v4</code> for API Level 4 (devices with Android
1.6 or higher). See the <a
href="{@docRoot}guide/appendix/api-levels.html">Android API Levels</a> document for more information
about these values.</p>
        <p class="caution"><strong>Caution:</strong> Android 1.5 and 1.6 only match resources
with this qualifier when it exactly matches the system version. See the section below about <a
href="#KnownIssues">Known Issues</a> for more information.</p>
      </td>
    </tr>
</table>


<h3 id="QualifierRules">Qualifier name rules</h3>

<p>Here are some rules about using configuration qualifier names:</p>

<ul>
    <li>You can specify multiple qualifiers for a single set of resources, separated by dashes. For
example, <code>drawable-en-rUS-land</code> applies to US-English devices in landscape
orientation.</li>
    <li>The qualifiers must be in the order listed in <a href="#table2">table 2</a>. For
example:
      <ul>
        <li>Wrong: <code>drawable-hdpi-port/</code></li>
        <li>Correct: <code>drawable-port-hdpi/</code></li>
      </ul>
    </li>
    <li>Alternative resource directories cannot be nested. For example, you cannot have
<code>res/drawable/drawable-en/</code>.</li>
    <li>Values are case-insensitive.  The resource compiler converts directory names
    to lower case before processing to avoid problems on case-insensitive
    file systems. Any capitalization in the names is only to benefit readability.</li>
    <li>Only one value for each qualifier type is supported. For example, if you want to use
the same drawable files for Spain and France, you <em>cannot</em> have a directory named
<code>drawable-rES-rFR/</code>. Instead you need two resource directories, such as
<code>drawable-rES/</code> and <code>drawable-rFR/</code>, which contain the appropriate files.
However, you are not required to actually duplicate the same files in both locations. Instead, you
can create an alias to a resource. See <a href="#AliasResources">Creating
alias resources</a> below.</li>
</ul>

<p>After you save alternative resources into directories named with
these qualifiers, Android automatically applies the resources in your application based on the
current device configuration. Each time a resource is requested, Android checks for alternative
resource directories that contain the requested resource file, then <a href="#BestMatch">finds the
best-matching resource</a> (discussed below). If there are no alternative resources that match
a particular device configuration, then Android uses the corresponding default resources (the
set of resources for a particular resource type that does not include a configuration
qualifier).</p>



<h3 id="AliasResources">Creating alias resources</h3>

<p>When you have a resource that you'd like to use for more than one device
configuration (but do not want to provide as a default resource), you do not need to put the same
resource in more than one alternative resource directory. Instead, you can (in some cases) create an
alternative
resource that acts as an alias for a resource saved in your default resource directory.</p>

<p class="note"><strong>Note:</strong> Not all resources offer a mechanism by which you can
create an alias to another resource. In particular, animation, menu, raw, and other unspecified
resources in the {@code xml/} directory do not offer this feature.</p>

<p>For example, imagine you have an application icon, {@code icon.png}, and need unique version of
it for different locales. However, two locales, English-Canadian and French-Canadian, need to
use the same version. You might assume that you need to copy the same image
into the resource directory for both English-Canadian and French-Canadian, but it's
not true. Instead, you can save the image that's used for both as {@code icon_ca.png} (any
name other than {@code icon.png}) and put
it in the default {@code res/drawable/} directory. Then create an {@code icon.xml} file in {@code
res/drawable-en-rCA/} and {@code res/drawable-fr-rCA/} that refers to the {@code icon_ca.png}
resource using the {@code &lt;bitmap&gt;} element. This allows you to store just one version of the
PNG file and two small XML files that point to it. (An example XML file is shown below.)</p>


<h4>Drawable</h4>

<p>To create an alias to an existing drawable, use the {@code &lt;bitmap&gt;} element.
For example:</p>

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

<p>If you save this file as {@code icon.xml} (in an alternative resource directory, such as
{@code res/drawable-en-rCA/}), it is compiled into a resource that you
can reference as {@code R.drawable.icon}, but is actually an alias for the {@code
R.drawable.icon_ca} resource (which is saved in {@code res/drawable/}).</p>


<h4>Layout</h4>

<p>To create an alias to an existing layout, use the {@code &lt;include&gt;}
element, wrapped in a {@code &lt;merge&gt;}. For example:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;merge>
    &lt;include layout="@layout/main_ltr"/>
&lt;/merge>
</pre>

<p>If you save this file as {@code main.xml}, it is compiled into a resource you can reference
as {@code R.layout.main}, but is actually an alias for the {@code R.layout.main_ltr}
resource.</p>


<h4>Strings and other simple values</h4>

<p>To create an alias to an existing string, simply use the resource ID of the desired
string as the value for the new string. For example:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;resources>
    &lt;string name="hello">Hello&lt;/string>
    &lt;string name="hi">@string/hello&lt;/string>
&lt;/resources>
</pre>

<p>The {@code R.string.hi} resource is now an alias for the {@code R.string.hello}.</p>

<p> <a href="{@docRoot}guide/topics/resources/more-resources.html">Other simple values</a> work the
same way. For example, a color:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;resources>
    &lt;color name="yellow">#f00&lt;/color>
    &lt;color name="highlight">@color/red&lt;/color>
&lt;/resources>
</pre>




<h2 id="Compatibility">Providing the Best Device Compatibility with Resources</h2>

<p>In order for your application to support multiple device configurations, it's very important that
you always provide default resources for each type of resource that your application uses.</p>

<p>For example, if your application supports several languages, always include a {@code
values/} directory (in which your strings are saved) <em>without</em> a <a
href="#LocaleQualifier">language and region qualifier</a>. If you instead put all your string files
in directories that have a language and region qualifier, then your application will crash when run
on a device set to a language that your strings do not support. But, as long as you provide default
{@code values/} resources, then your application will run properly (even if the user doesn't
understand that language&mdash;it's better than crashing).</p>

<p>Likewise, if you provide different layout resources based on the screen orientation, you should
pick one orientation as your default. For example, instead of providing layout resources in {@code
layout-land/} for landscape and {@code layout-port/} for portrait, leave one as the default, such as
{@code layout/} for landscape and {@code layout-port/} for portrait.</p>

<p>Providing default resources is important not only because your application might run on a
configuration you had not anticipated, but also because new versions of Android sometimes add
configuration qualifiers that older versions do not support. If you use a new resource qualifier,
but maintain code compatibility with older versions of Android, then when an older version of
Android runs your application, it will crash if you do not provide default resources, because it
cannot use the resources named with the new qualifier. For example, if your <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code
minSdkVersion}</a> is set to 4, and you qualify all of your drawable resources using <a
href="#NightQualifier">night mode</a> ({@code night} or {@code notnight}, which were added in API
Level 8), then an API Level 4 device cannot access your drawable resources and will crash. In this
case, you probably want {@code notnight} to be your default resources, so you should exclude that
qualifier so your drawable resources are in either {@code drawable/} or {@code drawable-night/}.</p>

<p>So, in order to provide the best device compatibility, always provide default
resources for the resources your application needs to perform properly. Then create alternative
resources for specific device configurations using the configuration qualifiers.</p>

<p>There is one exception to this rule: If your application's <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is 4 or
greater, you <em>do not</em> need default drawable resources when you provide alternative drawable
resources with the <a href="#DensityQualifier">screen density</a> qualifier. Even without default
drawable resources, Android can find the best match among the alternative screen densities and scale
the bitmaps as necessary. However, for the best experience on all types of devices, you should
provide alternative drawables for all three types of density. If your <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code minSdkVersion}</a> is
<em>less than</em> 4 (Android 1.5 or lower), be aware that the screen size, density, and aspect
qualifiers are not supported on Android 1.5 or lower, so you might need to perform additional
compatibility for these versions.</p>


<h3 id="ScreenCompatibility">Providing screen resource compatibility for Android 1.5</h3>

<p>Android 1.5 (and lower) does not support the following configuration qualifers:</p>
<dl>
  <dt><a href="#DensityQualifier">Density</a></dt>
    <dd>{@code ldpi}, {@code mdpi}, {@code ldpi}, and {@code nodpi}</dd>
  <dt><a href="#ScreenSizeQualifier">Screen size</a></dt>
    <dd>{@code small}, {@code normal}, and {@code large}</dd>
  <dt><a href="#ScreenAspectQualifier">Screen aspect</a></dt>
    <dd>{@code long} and {@code notlong}</dd>
</dl>

<p>These configuration qualifiers were introduced in Android 1.6, so Android 1.5 (API Level 3) and
lower does not support them. If you use these configuration qualifiers and do not provide
corresponding default resources, then an Android 1.5 device might use any one of the resource
directories named with the above screen configuration qualifiers, because it ignores these
qualifiers and uses whichever otherwise-matching drawable resource it finds first.</p>

<p>For example, if your application supports Android 1.5 and includes drawable resources for
each density type ({@code drawable-ldpi/}, {@code drawable-mdpi/}, and {@code drawable-ldpi/}),
and does <em>not</em> include default drawable resources ({@code drawable/}), then
an Android 1.5 will use drawables from any one of the alternative resource directories, which
can result in a user interface that's less than ideal.<p>

<p>So, to provide compatibility with Android 1.5 (and lower) when using the screen configuration
qualifiers:</p>
<ol>
  <li>Provide default resources that are for medium-density, normal, and notlong screens.

    <p>Because all Android 1.5 devices have medium-density, normal, not-long screens, you can
place these kinds of resources in the corresponding default resource directory. For example, put all
medium density drawable resources in {@code drawable/} (instead of {@code drawable-mdpi/}),
put {@code normal} size resources in the corresponding default resource directory, and {@code
notlong} resources in the corresponding default resource directory.</p>
  </li>

  <li>Ensure that your <a href="{@docRoot}sdk/tools-notes.html">SDK Tools</a> version
is r6 or greater.

    <p>You need SDK Tools, Revision 6 (or greater), because it includes a new packaging tool that
automatically applies an appropriate <a href="#VersionQualifier">version qualifier</a> to any
resource directory named with a qualifier that does not exist in Android 1.0. For example, because
the density qualifier was introduced in Android 1.6 (API Level 4), when the packaging tool
encounters a resource directory using the density qualifier, it adds {@code v4} to the directory
name to ensure that older versions do not use those resources (only API Level 4 and higher support
that qualifier). Thus, by putting your medium-density resources in a directory <em>without</em> the
{@code mdpi} qualifier, they are still accessible by Android 1.5, and any device that supports the
density qualifer and has a medium-density screen also uses the default resources (which are mdpi)
because they are the best match for the device (instead of using the {@code ldpi} or {@code hdpi}
resources).</p>
</li>
</ol>

<p class="note"><strong>Note:</strong> Later versions of Android, such as API Level 8,
introduce other configuration qualifiers that older version do not support. To provide the best
compatibility, you should always include a set of default resources for each type of resource
that your application uses, as discussed above to provide the best device compatibility.</p>



<h2 id="BestMatch">How Android Finds the Best-matching Resource</h2>

<p>When you request a resource for which you provide alternatives, Android selects which
alternative resource to use at runtime, depending on the current device configuration. To
demonstrate how Android selects an alternative resource, assume the following drawable directories
each contain different versions of the same images:</p>

<pre class="classic no-pretty-print">
drawable/
drawable-en/
drawable-fr-rCA/
drawable-en-port/
drawable-en-notouch-12key/
drawable-port-ldpi/
drawable-port-notouch-12key/
</pre>

<p>And assume the following is the device configuration:</p>

<p style="margin-left:1em;">
Locale = <code>en-GB</code> <br/>
Screen orientation = <code>port</code> <br/>
Screen pixel density = <code>hdpi</code> <br/>
Touchscreen type = <code>notouch</code> <br/>
Primary text input method = <code>12key</code>
</p>

<p>By comparing the device configuration to the available alternative resources, Android selects
drawables from {@code drawable-en-port}. It arrives at this decision using the following logic:</p>


<div class="figure" style="width:280px">
<img src="{@docRoot}images/resources/res-selection-flowchart.png" alt="" height="590" />
<p class="img-caption"><strong>Figure 2.</strong> Flowchart of how Android finds the
best-matching resource.</p>
</div>


<ol>
  <li>Eliminate resource files that contradict the device configuration.
    <p>The <code>drawable-fr-rCA/</code> directory is eliminated, because it
contradicts the <code>en-GB</code> locale.</p>
<pre class="classic no-pretty-print">
drawable/
drawable-en/
<strike>drawable-fr-rCA/</strike>
drawable-en-port/
drawable-en-notouch-12key/
drawable-port-ldpi/
drawable-port-notouch-12key/
</pre>
<p class="note"><strong>Exception:</strong> Screen pixel density is the one qualifier that is not
eliminated due to a contradiction. Even though the screen density of the device is hdpi,
<code>drawable-port-ldpi/</code> is not eliminated because every screen density is
considered to be a match at this point. More information is available in the <a
href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
Screens</a> document.</p></li>

  <li>Pick the (next) highest-precedence qualifier in the list (<a href="#table2">table 2</a>).
(Start with MCC, then move down.) </li>
  <li>Do any of the resource directories include this qualifier?  </li>
    <ul>
      <li>If No, return to step 2 and look at the next qualifier. (In the example,
  the answer is &quot;no&quot; until the language qualifier is reached.)</li>
      <li>If Yes, continue to step 4.</li>
    </ul>
  </li>

  <li>Eliminate resource directories that do not include this qualifier. In the example, the system
eliminates all the directories that do not include a language qualifier:</li>
<pre class="classic no-pretty-print">
<strike>drawable/</strike>
drawable-en/
drawable-en-port/
drawable-en-notouch-12key/
<strike>drawable-port-ldpi/</strike>
<strike>drawable-port-notouch-12key/</strike>
</pre>
<p class="note"><strong>Exception:</strong> If the qualifier in question is screen pixel density,
Android selects the option that most closely matches the device screen density.
In general, Android prefers scaling down a larger original image to scaling up a smaller
original image. See <a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple
Screens</a>.</p>
  </li>

  <li>Go back and repeat steps 2, 3, and 4 until only one directory remains. In the example, screen
orientation is the next qualifier for which there are any matches.
So, resources that do not specify a screen orientation are eliminated:
<pre class="classic no-pretty-print">
<strike>drawable-en/</strike>
drawable-en-port/
<strike>drawable-en-notouch-12key/</strike>
</pre>
<p>The remaining directory is {@code drawable-en-port}.</p>
  </li>
</ol>

<p>Though this procedure is executed for each resource requested, the system further optimizes
some aspects. One such optimization is that once the device configuration is known, it might
eliminate alternative resources that can never match. For example, if the configuration
language is English ("en"), then any resource directory that has a language qualifier set to
something other than English is never included in the pool of resources checked (though a
resource directory <em>without</em> the language qualifier is still included).</p>

<p class="note"><strong>Note:</strong> The <em>precedence</em> of the qualifier (in <a
href="#table2">table 2</a>) 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 than these other qualifiers, so
<code>drawable-port-notouch-12key</code> is out.</p>

<p>To learn more about how to use resources in your application, continue to <a
href="accessing-resources.html">Accessing Resources</a>.</p>




<h2 id="KnownIssues">Known Issues</h2>

<h3>Android 1.5 and 1.6: Version qualifier performs exact match, instead of best match</h3>

<p>The correct behavior is for the system to match resources marked with a <a
href="#VersionQualifier">version qualifier</a> equal
to or less than the system version on the device, but on Android 1.5 and 1.6, (API Level 3 and 4),
there is a bug that causes the system to match resources marked with the version qualifier
only when it exactly matches the version on the device.</p>

<p><b>The workaround:</b> To provide version-specific resources, abide by this behavior. However,
because this bug is fixed in versions of Android available after 1.6, if
you need to differentiate resources between Android 1.5, 1.6, and later versions, then you only need
to apply the version qualifier to the 1.6 resources and one to match all later versions. Thus, this
is effectively a non-issue.</p>

<p>For example, if you want drawable resources that are different on each Android 1.5, 1.6,
and 2.0.1 (and later), create three drawable directories: {@code drawable/} (for 1.5 and lower),
{@code drawable-v4} (for 1.6), and {@code drawable-v6} (for 2.0.1 and later&mdash;version 2.0, v5,
is no longer available).</p>