android_frameworks_base/docs/html/guide/practices/screen-compat-mode.jd

page.title=Screen Compatibility Mode
parent.title=Supporting Multiple Screens
parent.link=screens_support.html

@jd:body


<div id="qv-wrapper">
<div id="qv">

<h2>In this document</h2>
<ol>
  <li><a href="#Disable">Disabling Screen Compatibility Mode</a></li>
  <li><a href="#Enable">Enabling Screen Compatibility Mode</a></li>
</ol>
<h2>See also</h2>
<ol>
  <li><a href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple Screens</a></li>
  <li><a href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a></li>
</ol>
</div>
</div>

<div class="figure" style="width:500px;">
<a href="{@docRoot}images/screens_support/compat-zoom.png">
<img src="{@docRoot}images/screens_support/compat-zoom-thumb.png" alt="" />
</a>
<p class="img-caption"><strong>Figure 1.</strong> An application running in compatibility mode
on an Android 3.2 tablet.</p>
</div>

<div class="figure" style="width:500px;">
<a href="{@docRoot}images/screens_support/compat-stretch.png">
<img src="{@docRoot}images/screens_support/compat-stretch-thumb.png" alt="" />
</a>
<p class="img-caption"><strong>Figure 2.</strong> The same application from figure 1, with
compatibility mode disabled.</p>
</div>

<p class="caution"><strong>Notice:</strong> If you've developed an application for a version of
Android lower than Android 3.0, but it does resize properly for larger screens such as tablets, you
should disable screen compatibility mode in order to maintain the best user experience. To learn how
to quickly disable the user option, jump to <a href="#Disable">Disabling Screen Compatibility
Mode</a>.</p>

<p>Screen compatibility mode is an escape hatch for applications that are not properly designed
to resize for larger screens such as tablets. Since Android 1.6, Android has supported a
variety of screen sizes and does most of the work to resize application layouts so that they
properly fit each screen. However, if your application does not successfully follow the guide to
<a href="{@docRoot}guide/topics/practices/screens_support.html">Supporting Multiple Screens</a>,
then it might encounter some rendering issues on larger screens. For applications with this
problem, screen compatibility mode can make the application a little more usable on larger
screens.</p>

<p>There are two versions of screen compatibility mode with slightly different behaviors:</p>
<dl>
  <dt>Version 1 (Android 1.6 - 3.1)</dt>
  <dd>The system draws the application's UI in a "postage stamp"
window. That is, the system draws the application's layout the same as it would on a
normal size handset (emulating a 320dp x 480dp screen), with a black border that fills
the remaining area of the screen.

<p>This was introduced with Android 1.6 to handle apps that were designed only for the
original screen size of 320dp x 480dp. Because there are so few active devices remaining that run
Android 1.5, almost all applications should be developed against Android 1.6 or greater and
should not have version 1 of screen compatibility mode enabled for larger screens. This version
is considered obsolete.</p>
  <p>To disable this version of screen compatibility mode, you simply need to set <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code
android:minSdkVersion}</a> or <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code
android:targetSdkVersion}</a> to {@code "4"} or higher, or set <a
href="guide/topics/manifest/supports-screens-element.html#resizeable">{@code
android:resizeable}</a> to {@code "true"}.</p>
  </dd>
  
  <dt>Version 2 (Android 3.2 and greater)</dt>
  <dd>The system draws the application's layout the same as
it would on a normal size handset (approximately emulating a 320dp x 480dp screen), then scales it
up to fill the screen. This essentially "zooms" in on your layout to make it bigger,
which will usually cause artifacts such as blurring and pixelation in your UI.
  <p>This was introduced with Android 3.2 to further
assist applications on the latest tablet devices when the applications have not yet
implemented techniques for <a
href="{@docRoot}guide/topics/practices/screens_support.html">Supporting Multiple
Screens</a>.</p>
  <p>In general, large screen devices running Android 3.2 or higher allow users to enable
screen compatibility mode when the application does not <strong>explicitly declare that it supports
large screens</strong> in the manifest file. When this is the case, an icon (with
outward-pointing arrows) appears next to the clock in the system bar, which allows the user to
toggle screen compatibility mode on and off (figure 3). An application can also explicitly
declare that it <em>does not</em> support large screens such that screen compatibility mode
is always enabled and the user cannot disable it. (How to declare your application's
support for large screens is discussed in the following sections.)</p></dd>
</dl>

<img src="{@docRoot}images/screens_support/compat-toggle.png" alt="" />
<p class="img-caption"><strong>Figure 3.</strong> The pop up menu to toggle screen compatibility
mode (currently disabled, so normal resizing occurs).</p>

<p>As a developer, you have control over when your application uses screen compatibility mode. The
following sections describe how you can choose to disable or enable screen compatibility mode for
larger screens when running Android 3.2 or higher.</p>


<h2 id="Disable">Disabling Screen Compatibility Mode</h2>

<p>If you've developed your application primarily for versions of Android lower than 3.0, but
<strong>your application does resize properly</strong> for larger screens such as tablets,
<strong>you should disable screen compatibility mode</strong> in order to maintain the best user
experience. Otherwise, users may enable screen compatibility mode and experience your application in
a less-than-ideal format.</p>

<p>By default, screen compatibility mode for devices running Android 3.2 and higher is offered to
users as an optional feature when one of the following is true:</p>

<ul>
  <li>Your application has set both <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>
and <a href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code
android:targetSdkVersion}</a> to {@code "10"} or lower and <strong>does not explicitly
declare support</strong> for large screens using the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element.</li>

  <li>Your application has set either <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>
or <a href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code
android:targetSdkVersion}</a> to {@code "11"} or higher and <strong>explicitly declares that it does
not support</strong> large screens, using the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element.</li>
</ul>

<p>To completely disable the user option for screen compatibility mode and remove the icon in the
system bar, you can do one of the following:</p>

<ul>
  <li><strong>Easiest:</strong>
    <p>In your manifest file, add the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element and specify the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html#xlarge">{@code
android:xlargeScreens}</a> attribute to {@code "true"}:</p>
<pre>
&lt;supports-screens android:xlargeScreens="true" /&gt;
</pre>
  <p>That's it. This declares that your application supports all larger screen sizes, so the
system will always resize your layout to fit the screen. This works regardless of what values
you've set in the <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html">{@code &lt;uses-sdk&gt;}</a>
attributes.</p> 
  </li>
  
  <li><strong>Easy but has other effects:</strong>
    <p>In your manifest's <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html">{@code &lt;uses-sdk&gt;}</a>
element, set <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code
android:targetSdkVersion}</a> to {@code "11"} or higher:</p>
<pre>
&lt;uses-sdk android:minSdkVersion="4" android:targetSdkVersion="11" /&gt;
</pre>
  <p>This declares that your application supports Android 3.0 and, thus, is designed to
work on larger screens such as tablets.</p>
  <p class="caution"><strong>Caution:</strong> When running on Android 3.0 and greater, this also
has the effect of enabling the Holographic theme for you UI, adding the <a
href="{@docRoot}guide/topics/ui/actionbar.html">Action Bar</a> to your activities, and removing the
Options Menu button in the system bar.</p>
  <p>If screen compatibility mode is still enabled after you change this, check your manifest's <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> and be sure that there are no attributes set {@code "false"}. The best
practice is to always explicitly declare your support for different screen sizes using the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element, so you should use this element anyway.</p>
  <p>For more information about updating your application to target Android 3.0 devices, read <a
href="{@docRoot}guide/practices/optimizing-for-3.0.html">Optimizing Apps for Android
3.0</a>.</p>
  </li>
<!--
  <li><strong>Most control</strong> (but you must compile against Android 3.2 or higher):
    <p>In your manifest file, add the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element and specify the {@code android:compatibleWidthLimitDp}
attribute to any value <em>higher than</em> {@code "320"}:</p>
<pre>
&lt;supports-screens android:compatibleWidthLimitDp="720" /&gt;
</pre>
  <p>Using this technique allows you to specify exactly what your application's limit is for
layout resizing. Normally, only applications that are already built against Android 3.2 (or
higher) use this attribute, because the primary intention is to specify at what size should screen
compatibility mode actually be offered to users.</p>
  <p class="note"><strong>Note:</strong> Currently, screen compatibility mode only emulates
handset screens with a 320dp width, so screen compatibility mode is not applied to any device if
your value for {@code android:compatibleWidthLimitDp} is larger than 320.</p>
  </li>
  -->
</ul>



<h2 id="Enable">Enabling Screen Compatibility Mode</h2>

<p>When your application is targeting Android 3.2 (API level 13) or higher, you can affect
whether compatibility mode is enabled for certain screens by using the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens>}</a> element.</p>

<p class="note"><strong>Note:</strong> Screen compatibility mode is <strong>not</strong> a mode in
which you should want your application to run&mdash;it causes pixelation and blurring in your UI,
due to zooming. The proper way to make your application work well on large screens is to follow the
guide to <a
href="{@docRoot}guide/topics/practices/screens_support.html">Supporting Multiple Screens</a> and
provide alternative layouts for different screen sizes.</p>

<p>By default, when you've set either <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code
android:minSdkVersion}</a> or <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code
android:targetSdkVersion}</a> to {@code "11"} or higher, screen compatibility mode is
<strong>not</strong> available to users. If either of these are true and your application does not
resize properly for larger screens, you can choose to enable screen compatibility mode in one
of the following ways:</p>

<ul>
  <li>In your manifest file, add the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code
&lt;supports-screens&gt;}</a> element and specify the <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html#compatibleWidth">{@code
android:compatibleWidthLimitDp}</a> attribute to {@code "320"}:</p>
<pre>
&lt;supports-screens android:compatibleWidthLimitDp="320" /&gt;
</pre>
  <p>This indicates that the maximum "smallest screen width" for which your application is designed
is 320dp. This way, any devices with their smallest side being larger than this value will offer
screen compatibility mode as a user-optional feature.</p>
  <p class="note"><strong>Note:</strong> Currently, screen compatibility mode only emulates
handset screens with a 320dp width, so screen compatibility mode is not applied to any device if
your value for <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html#compatibleWidth">{@code
android:compatibleWidthLimitDp}</a> is larger than 320.</p>
  </li>

  <li>If your application is functionally broken when resized for large screens and you want to
force users into screen compatibility mode (rather than simply providing the option), you can use
the <a href="{@docRoot}guide/topics/manifest/supports-screens-element.html#largestWidth">{@code
android:largestWidthLimitDp}</a> attribute:
<pre>
&lt;supports-screens android:largestWidthLimitDp="320" /&gt;
</pre>
  <p>This works the same as <a
href="{@docRoot}guide/topics/manifest/supports-screens-element.html#compatibleWidth">{@code
android:compatibleWidthLimitDp}</a> except it force-enables
screen compatibility mode and does not allow users to disable it.</p>
  </li>
</ul>