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Commit 6aa2b625 authored by Scott Main's avatar Scott Main
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docs: update screen support doc to de-emphasize support for 1.5 

this includes a variety of other revisions to reorganize some of the content in the main document
and also add separate documents for how to enable screen filtering and add screen support on 1.5

For more change history, also see Change-Id: Iadebc9ca3f2f5a0e7490466811f0d741fe2b2b8c

Change-Id: I78825116f5f7825da42120e840e5bc6d8d1e359c
parent 5cf78ecd

docs/html/guide/guide_toc.cs

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@@ -652,9 +652,19 @@ 
      <li><a href="<?cs var:toroot ?>guide/practices/compatibility.html">

            <span class="en">Compatibility</span>

          </a></li>

      <li><a href="<?cs var:toroot ?>guide/practices/screens_support.html">

      <li class="toggle-list">

        <div><a href="<?cs var:toroot ?>guide/practices/screens_support.html">

          <span class="en">Supporting Multiple Screens</span>

        </a></div>

        <ul>

          <li><a href="<?cs var:toroot ?>guide/practices/screens-distribution.html">

            <span class="en">Distributing to Specific Screens</span>

          </a></li>

          <li><a href="<?cs var:toroot ?>guide/practices/screens-support-1.5.html">

            <span class="en">Strategies for Android 1.5</span>

          </a></li>

        </ul>

      </li>

      <li><a href="<?cs var:toroot ?>guide/practices/optimizing-for-3.0.html">

            <span class="en">Optimizing Apps for Android 3.0</span>

          </a></li>

docs/html/guide/practices/screens-distribution.jd

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page.title=Distributing to Specific Screens

parent.title=Supporting Multiple Screens

parent.link=screens_support.html



@jd:body



<div id="qv-wrapper">

<div id="qv">



  <h2>Quickview</h2>

  <ul>

    <li>If necessary, you can control distribution of your application based on the device

screen configuration</li>

  </ul>



  <h2>In this document</h2>

  <ol>

    <li><a href="#FilteringHansetApps">Filtering a Handset Application from Tablets</a></li>

    <li><a href="#FilteringTabletApps">Filtering a Tablet Application from Handsets</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/practices/optimizing-for-3.0.html">Optimizing Apps for Android 3.0</a></li>

  </ol>



</div>

</div>







<p>Although we recommend that you design your application to function properly on multiple

configurations of screen size and density, you can instead choose to limit the distribution of your

application to certain types of screens, such as only tablets and other large devices or only

handsets and similar-sized devices. To do so, you can enable filtering by external services such as

Android Market by adding elements to your manifest file that specify the screen configurations your

application supports.</p>



<p>However, before you decide to restrict your application to certain screen configurations, you

should understand the techniques for <a

href="{@docRoot}guide/practices/screens_support.html">supporting multiple screens</a> and implement

them to the best of your ability. By supporting multiple screens, your application can be made

available to the greatest number of users with different devices, using a single {@code .apk}.</p>







<h2 id="FilteringHandsetApps">Filtering a Handset Application from Tablets</h2>



<p>Because the system generally scales applications to fit larger screens well, you shouldn't

need to filter your application from larger screens. As long as you follow the <a

href="{@docRoot}guide/practices/screens_support.html#screen-independence">Best Practices for Screen

Independence</a>, your application should work well on larger screens such as tablets. However, you

might discover that your application can't scale up well or perhaps you've decided to publish two

versions of your application for different screen configurations. In such a case, you can use the <a

href="{@docRoot}guide/topics/manifest/compatible-screens-element.html">{@code

&lt;compatible-screens>}</a> element to manage the distribution of your application based on

combinations of screen size and density. External services such as Android Market use this

information to apply filtering to your application, so that only devices that have a screen

configuration with which you declare compatibility can download your application.</p>



<p>The <a href="{@docRoot}guide/topics/manifest/compatible-screens-element.html">{@code

&lt;compatible-screens>}</a> element must contain one or more {@code &lt;screen&gt;} elements. Each

{@code &lt;screen&gt;} element specifies a screen configuration with which your application is

compatible, using both the {@code android:screenSize} and {@code android:screenDensity} attributes.

Each {@code &lt;screen&gt;} element <strong>must include both attributes</strong> to specify an

individual screen configuration&mdash;if either attribute is missing, then the element is invalid

(external services such as Android Market will ignore it).</p>



<p>For example, if your application is compatible with only small and normal size screens,

regardless of screen density, you must specify eight different {@code &lt;screen&gt;} elements,

because each screen size has four density configurations. You must declare each one of

these; any combination of size and density that you do <em>not</em> specify is considered a screen

configuration with which your application is <em>not</em> compatible. Here's what the manifest

entry looks like if your application is compatible with only small and normal screen sizes:</p>



<pre>

&lt;manifest ... >

    ...

    &lt;compatible-screens>

        &lt;!-- all small size screens -->

        &lt;screen android:screenSize="small" android:screenDensity="ldpi" />

        &lt;screen android:screenSize="small" android:screenDensity="mdpi" />

        &lt;screen android:screenSize="small" android:screenDensity="hdpi" />

        &lt;screen android:screenSize="small" android:screenDensity="xhdpi" />

        &lt;!-- all normal size screens -->

        &lt;screen android:screenSize="normal" android:screenDensity="ldpi" />

        &lt;screen android:screenSize="normal" android:screenDensity="mdpi" />

        &lt;screen android:screenSize="normal" android:screenDensity="hdpi" />

        &lt;screen android:screenSize="normal" android:screenDensity="xhdpi" />

    &lt;/compatible-screens>

    &lt;application ... >

        ...

    &lt;application>

&lt;/manifest>

</pre>



<p class="note"><strong>Note:</strong> Although you can also use the <a

href="{@docRoot}guide/topics/manifest/compatible-screens-element.html">{@code

&lt;compatible-screens>}</a> element for the reverse scenario (when your application is not

compatible with smaller screens), it's easier if you instead use the <a

href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code

&lt;supports-screens>}</a> as discussed in the next section, because it doesn't require you

to specify each screen density your application supports.</p>







<h2 id="FilteringTabletApps">Filtering a Tablet Application from Handsets</h2>



<p>If your application's UI is adversely affected when the system scales your application down to

smaller screens, you should add <a

href="{@docRoot}guide/topics/resources/providing-resources.html#AlternativeResources">alternative

layouts</a> for smaller screens to adjust the layout for those screens. However, sometimes your

layout still might not fit a smaller screen or you've explicitly designed your application only for

tablets and other large devices. In this case, you can manage the availability of your application

to smaller screens by using the <a

href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code

&lt;supports-screens>}</a> manifest element.</p>



<p>For example, if you want your application to be available only to large and extra large

screens, you can declare the element in your manifest like this:</p>



<pre>

&lt;manifest ... >

    ...

    &lt;supports-screens android:smallScreens="false"

                      android:normalScreens="false"

                      android:largeScreens="true"

                      android:xlargeScreens="true" /&gt;

    &lt;application ... >

        ...

    &lt;application>

&lt;/manifest>

</pre>



<p>External services such as Android Market read this manifest element and use it to ensure that

your application is available only to devices with either a large or an extra large screen.</p>



<p class="caution"><strong>Caution:</strong> If you use the <a

href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code

&lt;supports-screens>}</a> element for the reverse scenario (when your application is not compatible

with <em>larger</em> screens) and set the larger screen size attributes to {@code "false"}, then

external services such as Android Market <strong>do not</strong> apply filtering. Your application

will still be available to larger screens, but when it runs, it will not resize to fit the screen.

Instead, the system will draw it in a "postage stamp" window that's the same relative size as the

screen size that your application does support (see <a

href="screens-support-1.5.html#CompatMode">compatibility mode</a> for more information). If you want

to prevent your application from being downloaded on larger screens, use <a

href="{@docRoot}guide/topics/manifest/compatible-screens-element.html">{@code

&lt;compatible-screens>}</a>, as discussed in the previous section about <a

href="#FilteringHandsetApps">Filtering a Handset Application from Tablets</a>.</p>



<p>Remember, you should strive to make your application available to as many devices as possible by

applying all necessary techniques for <a

href="{@docRoot}guide/practices/screens_support.html">supporting multiple screens</a>. You should

use <a href="{@docRoot}guide/topics/manifest/compatible-screens-element.html">{@code

&lt;compatible-screens>}</a> or <a

href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code

&lt;supports-screens>}</a> only when you cannot provide compatibility on all screen configurations

or you have decided to provide different versions of your application for different sets of screen

configurations.</p>

docs/html/guide/practices/screens-support-1.5.jd

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page.title=Strategies for Android 1.5

parent.title=Supporting Multiple Screens

parent.link=screens_support.html



@jd:body



<div id="qv-wrapper">

<div id="qv">



  <h2>Quickview</h2>

  <ul>

    <li>Apps developed for Android 1.5 and below support only the baseline screen

configuration, by default</li>

    <li>There are some simple steps you should take to enable support for multiple screens in

an application designed for Android 1.5</li>

  </ul>



  <h2>In this document</h2>

  <ol>

    <li><a href="#strategies">Adding Multiple Screens Support</a></li>

    <li><a href="#CompatMode">Compatibility Mode</a></li>

  </ol>



  <h2>See also</h2>

  <ol>

    <li><a

href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple Screens</a></li>

  </ol>



</div>

</div>





<p>All applications written for Android 1.5 or earlier, by default, support only the

baseline HVGA screen used on the T-Mobile G1 and similar devices, which is <em>normal</em> screen

size and medium density (<em>mdpi</em>). Android 1.6 introduced support for different screen

configurations and added APIs that allow applications to control how they operate on different

screens, using alternative resources for different screen configurations.</p>



<p>If your manifest file includes the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html">{@code &lt;uses-sdk&gt;}</a> element,

with the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>

attribute set to {@code "3"} or lower, and does <em>not</em> include the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code

android:targetSdkVersion}</a> set to {@code "4"} or higher, then this document is for you. By

default, an application written for Android 1.5 or below that does not set the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code

android:targetSdkVersion}</a> set to {@code "4"} or higher runs in <a

href="#CompatMode">compatibility mode</a> when on a device with a screen larger than the

<em>normal</em> screen size (basically, the system displays the application in a small window

that is roughly the size of the normal screen size).</p>



<p>This document describes how to get your application out of <a href="#CompatMode">compatibility

mode</a> and instead support multiple screens, but also maintain compatibility with Android 1.5 and

below.</p>



<p class="note"><strong>Note:</strong> Before you begin, you should first decide whether it's even

necessary to support Android 1.5. To see the relative number of devices that are still running

Android 1.5, see the <a

href="http://developer.android.com/resources/dashboard/platform-versions.html">Platform Versions

Dashboard</a>.</p>









<h2 id="strategies">Adding Multiple Screens Support</h2>



<p>If you have already developed and published an Android application based on

Android 1.5 or earlier platform version, and want to maintain compatibility with Android 1.5, you

need to make some changes to your application in order for it to properly run on newer devices with

different screen configurations. You should be able to make these changes to your application such

that you can distribute a single {@code .apk} to all devices.</p>



<p>The recommended strategy is to develop your application against Android 1.6 (because it's the

lowest version that includes support for multiple screens) and test your application on each

platform version your application supports (especially the minimum platform, such as Android 1.5).

Here's how to do that:</p>



<ol>

  <li>Maintain compatibility with existing devices by leaving your application's <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>

attribute as it is. You <em>do not</em> need to increment the value of the attribute to support new

devices and multiple screens. </li>

  <li>Extend compatibility for Android 1.6 (and higher) devices by adding <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code

android:targetSdkVersion}</a> to the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html">{@code &lt;uses-sdk&gt;}</a> element.

Set the value of <a href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code

android:targetSdkVersion}</a> to <code>"4"</code>. This allows your application to "inherit" the

platform's multiple screens support, even though it is technically using an earlier version of the

API.

  <p>Adding this attribute will cause an error in the compiler, because the attribute is unknown to

Android 1.5. You'll fix this next.</p></li>

  <li>Change your application's build properties, such that it compiles against the Android 1.6 (API

Level 4) library, rather than against the Android 1.5 (or earlier) library. You must do this in

order for your application to successfully compile when using the new manifest attributes. Older

versions of the platform simply ignore the attributes they don't know, so your application still

runs fine on them, as long as you don't use APIs in your application code from Android 1.6. </li>

</ol>



<p>Your application is now prepared to run on multiple screens, while maintaining support for

Android 1.5 or lower.</p>



<p>Here's how you should begin testing your application:</p>



<ol>

  <li>Set up AVDs for testing your application on Android 1.6 and some new versions. Create AVDs

that use the screen sizes and densities that you want to support. When you create the AVDs, make

sure to select the Android 1.6 or higher platform as the system image to use. For more information,

see <a href="{@docRoot}guide/practices/screens_support.html#testing">How to Test Your Application on

Multiple Screens</a>.</li>

  <li>Set up AVDs for testing your application on older versions of the platform, as low as the

version declared by your <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code android:minSdkVersion}</a>.

You need AVDs running the older platforms you are targeting, so that you can ensure there are

no functional regressions.</li>

  <li>Compile your application against the Android 1.6 library and run it on the AVDs you created.

Observe the way your application looks and runs, and test all of the user interactions.</li>

  <li>Debug any display or functional issues. For issues that you resolve in

your application code, <span style="color:red">make certain not to use any APIs

introduced later than the version declared by your <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code

android:minSdkVersion}</a></span>. If you

are in doubt, refer to SDK reference documentation and look for the API Level specifier for the API

you want to use. Using newer APIs not supported by your minimum version will mean that your

application will no longer be compatible with devices running on that version.</li>

</ol>



<p>In particular, remember to test your application on an AVD that emulates a small-screen device.

Users of devices with QVGA resolution at low density may want to download your application, so you

should understand how your application will look and function on a small-screen device. In some

cases, the reduced screen area and density mean that you need to make tradeoffs in design on those

devices.</p>



<p>Also give extra attention to testing your application on an AVD that emulates an <em>xlarge</em>

screen. Devices with extra large screens are tablet-sized or larger, so you should pay close

attention to how usable your application is on such screens. You might want to design new layouts

specifically for extra large screens, to address usability aspects such as the location and size of

buttons in your UI. To test your application on an extra large screen, create an AVD targeted to

Android 3.0 and use the WXGA emulator skin.</p>



<p>Once you've completed the procedures above, you should follow the recommendations in <a

href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple Screens</a> to add

complete support for different screen configurations.</p>





<h2 id="CompatMode">Compatibility Mode</h2>



<div class="figure" style="width:450px;margin:0">

<img src="{@docRoot}images/screens_support/compat-mode-on.png" alt="" />

<p class="img-caption"><strong>Figure 1.</strong> An application running in compatibility mode

on an extra large screen.</p>

</div>



<p>To allow applications to run on larger screens without stretching the UI, Android provides a

compatibility mode that draws an application's UI in a "postage stamp" window when on larger

screens. That is, the system displays the application at the baseline size (<em>normal</em>) and

density (<em>mdpi</em>), with a black border that fills the rest of the screen.</p>



<p>Compatibility mode exists primarily to support application's developed for Android 1.5 (or lower)

when running on larger screens, because multiple screen support was not added until Android 1.6,

older applications were not designed to support different screen configurations.</p>



<p>As such, if you've set your <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#min">{@code

android:minSdkVersion}</a> to {@code "3"} or lower and have <em>not</em> set the <a

href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code

android:targetSdkVersion}</a> to {@code "4"} or higher, then compatibility mode is enabled and

the system will not scale your application, because your application implicitly declares that it

only supports the baseline screen configuration (normal screen size and medium density).</p>



<p>To disable compatibility mode, 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 "4"} or higher. For more information, see the previous

section about <a href="#strategies">Adding Multiple Screens Support</a>.</p>



<p>You can also affect whether compatibility mode is enabled by using the <a

href="{@docRoot}guide/topics/manifest/supports-screens-element.html">{@code

&lt;supports-screens>}</a> element (you can enable it by setting {@code android:resizeable} or

specific screen sizes to {@code "false"}). However, you should not explicitly enable compatibility

mode for your application, but should instead apply the necessary techniques to <a

href="{@docRoot}guide/practices/screens_support.html">supporting multiple screens</a> and allow your

application to properly fit the screen on all screen sizes.</p>

docs/html/guide/practices/screens_support.jd

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docs/html/guide/topics/resources/providing-resources.jd

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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>There is thus a 3:4:6:8 scaling ratio between the four densities, so a 9x9 bitmap

         in ldpi is 12x12 in mdpi, 18x18 in hdpi and 24x24 in xhdpi.</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