1 page.title=Android Compatibility 2 @jd:body 3 4 <div id="qv-wrapper"> 5 <div id="qv"> 6 7 <h2>See also</h2> 8 <ol> 9 <li><a 10 href="{@docRoot}guide/google/play/filters.html">Filtering on Google Play</a></li> 11 <li><a 12 href="{@docRoot}guide/topics/resources/providing-resources.html#AlternativeResources">Providing Alternative Resources</a></li> 13 <li><a 14 href="{@docRoot}guide/practices/screens_support.html">Supporting Multiple Screens</a></li> 15 <li style="margin-top:3px;"><code><a 16 href="{@docRoot}guide/topics/manifest/supports-screens-element.html"><supports-screens></a></code></li> 17 <li><code><a 18 href="{@docRoot}guide/topics/manifest/uses-configuration-element.html"><uses-configuration></a></code></li> 19 <li><code><a 20 href="{@docRoot}guide/topics/manifest/uses-feature-element.html"><uses-feature></a></code></li> 21 <li><code><a 22 href="{@docRoot}guide/topics/manifest/uses-library-element.html"><uses-library></a></code></li> 23 <li><code><a 24 href="{@docRoot}guide/topics/manifest/uses-permission-element.html"><uses-permission></a></code></li> 25 <li><code><a 26 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html"><uses-sdk></code></a></li> 27 </ol> 28 29 30 </div> </div> 31 32 <p>Android is designed to run on many different types of devices. For 33 developers, the range and number of devices means a huge potential audience: the 34 more devices that run Android apps, the more users who can access your app. In 35 exchange, however, it also means that your apps will have to cope with that same 36 variety of hardware.</p> 37 38 <p>Fortunately, Android has built-in tools and support that make it easy for 39 your apps to do that, while at the same time letting you maintain control of 40 what types of devices your app is available to. With a bit of forethought and 41 some minor changes in your app's manifest file, you can ensure that users 42 whose devices cant run your app will never see it on Google Play, and 43 will not get in trouble by downloading it. This page explains how you can 44 control which devices have access to your apps, and how to prepare your apps to 45 make sure they reach the right audience.</p> 46 47 48 <h3 id="defined">What does compatibility mean?</h3> 49 50 <p>A device is Android compatible if it can correctly run apps written for the 51 <em>Android execution environment</em>. The exact details of the Android execution 52 environment</em> are defined by the Android Compatibility Definition Document, 53 but the single most important characteristic of a compatible device is the 54 ability to install and correctly run an Android <code>.apk</code> file.</p> 55 56 <p>There is exactly one Android API for each <a 57 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#ApiLevels">API level</a>, and its the same 58 API no matter what kind of device its installed on. No parts of the API are 59 optional, and you never have to worry about parts of the API missing on some 60 devices. Every compatible Android device your app will land on will include 61 every class and every API for that API level.</p> 62 63 <p>Of course, some APIs wont work correctly if a particular device lacks the 64 corresponding hardware or feature. But thats not a problem: we also designed 65 Android to prevent apps from being visible to devices which dont have features 66 the apps require. Weve built support for this right into the SDK tools, and 67 its part of the Android platform itself, as well as part of Google Play.</p> 68 69 <p>As a developer, you have complete control of how and where your apps are 70 available. Android provides tools as a first-class part of the platform that let 71 you manage this. You control the availability of your apps, so that they reach 72 only the devices capable of running them.</p> 73 74 <h3 id="how">How does it work?</h3> 75 76 <p>You manage your apps availability through a simple three-step process:</p> 77 78 <ol> 79 <li>You state the features your app requires by declaring <a 80 href="{@docRoot}guide/topics/manifest/uses-feature-element.html"><code><uses-feature></code></a> 81 elements its manifest file.</li> 82 <li>Devices are required to declare the features they include to Google 83 Play.</li> 84 <li>Google Play uses your apps stated requirements to filter it from devices 85 that dont meet those requirements.</li> 86 </ol> 87 88 <p>This way, users never even see apps that wont work properly on their 89 devices. As long as you accurately describe your apps requirements, you dont 90 need to worry about users blaming you for compatibility problems.</p> 91 92 <p>If youre familiar with web development, you may recognize this model as 93 capability detection. Web developers typically prefer this approach to 94 browser detection, because its very difficult to keep up as new browsers and 95 new versions of current browsers are released. By checking for support for 96 specific required capabilities instead of the current browser, web developers 97 get better fine-grained control. Thats the same approach Android uses: since 98 its impossible to keep up with all the Android devices being released, you 99 instead use the fine-grained controls Android provides.</p> 100 101 <h3>Filtering for technical reasons</h3> 102 103 <div class="sidebox-wrapper"> 104 <img id="rule" src="{@docRoot}assets/images/grad-rule-qv.png"> 105 <div id="qv-sub-rule"> 106 <img src="{@docRoot}assets/images/icon_play.png" style="float:left;margin:0;padding:0;"> 107 <p style="color:#669999;">Filtering on Google Play</p> 108 109 <p>Google Play filters the applications that are visible to users, so 110 that users can see and download only those applications that are compatible with 111 their devices.</p> 112 113 <p style="margin-top:1em;">One of the ways Google Play filters applications is by 114 feature compatibility. To do this, Google Play checks the 115 <code><uses-feature></code> elements in each application's manifest, to 116 establish the app's feature needs. Google Play then shows or hides the application to 117 each user, based on a comparison with the features available on the user's 118 device. 119 120 <p style="margin-top:1em;">For information about other filters that you can 121 use to control the availability of your apps, see the 122 <a href="{@docRoot}guide/google/play/filters.html">Filters on Google Play</a> 123 document.</p> 124 </div> 125 </div> 126 127 <p>Android includes support for a lot of features, some hardware and some 128 software. Examples include compass and accelerometer sensors, cameras, and Live 129 Wallpapers. However, not every device will support every feature. For instance, 130 some devices dont have the hardware horsepower to display Live Wallpapers 131 well.</p> 132 133 <p>To manage this, Android defines <em>feature IDs</em>. Every capability has a 134 corresponding feature ID defined by the Android platform. For instance, the 135 feature ID for compass is <code>android.hardware.sensor.compass</code>, 136 while the feature 137 ID for Live Wallpapers is <code>android.software.live_wallpapers</code>. Each of these IDs 138 also has a corresponding Java-language constant on the 139 {@link android.content.pm.PackageManager} class that you can use to query whether 140 feature is supported at runtime. As Android adds support for new features in 141 future versions, new feature IDs will be added as well.</p> 142 143 <p>When you write your application, you specify which features your app requires 144 by listing their feature IDs in <code><uses-feature></code> elements in 145 the <code>AndroidManifest.xml</code> file. This is the information that Google 146 Play uses to match your app to devices that can run it. For instance, if you 147 state that your app requires android.software.live_wallpapers, it wont be shown 148 to devices that dont support Live Wallpapers.</p> 149 150 <p>This puts you in total control of your app — because you dont have to 151 declare these features. Consider an example involving cameras.</p> 152 153 <p>If youre building a really impressive next-generation augmented-reality app, 154 your app wont function at all without a camera. However, if youre building a 155 shopping app that only uses the camera for barcode scanning, users without 156 cameras might still find it useful even if they cant scan barcodes. While both 157 apps need to acquire the permission to access the camera, only the first app 158 needs to state that it requires a camera. (The shopping app can simply check at 159 runtime and disable the camera-related features if theres no camera 160 present.)</p> 161 162 <p>Since only you can say what the best approach is for your app, Android 163 provides the tools and lets you make your own tradeoff between maximizing 164 audience size and minimizing development costs.</p> 165 166 167 <h3 id="filtering">Filtering for business reasons</h3> 168 169 <p>Its possible that you may need to restrict your apps availability for 170 business or legal reasons. For instance, an app that displays train schedules 171 for the London Underground is unlikely to be useful to users outside the United 172 Kingdom. Other apps might not be permitted in certain countries for business or 173 legal reasons. For cases such as these, Google Play itself provides 174 developers with filtering options that allow them control their apps 175 availability for non-technical reasons.</p> 176 177 <p>The help information for Google Play provides full details, but in a 178 nutshell, developers can use the Google Play publisher UI to:</p> 179 180 <ul> 181 <li>List the countries an app is available in.</li> 182 <li>Select which carriers users are able to access the app.</li> 183 </ul> 184 185 <p>Filtering for technical compatibility (such as required hardware components) 186 is always based on information contained within your <code>.apk</code> file. But 187 filtering for non-technical reasons (such as geographic restrictions) is always 188 handled in the Google Play user interface.</p> 189 190 <h3 id="futureproofing">Future-proofing</h3> 191 192 <p>Theres one additional quirk that we havent yet addressed: protecting apps 193 from changes made to future versions of Android. If the Android platform 194 introduces a new feature or changes how existing features are handled, what 195 happens to existing apps that were written without any knowledge of the new 196 behavior?</p> 197 198 <p>Simply put, Android commits to not making existing apps available to devices 199 where they wont work properly, even when the platform changes. The best way to 200 explain this is through examples, so here are two:</p> 201 202 <ul> 203 <li>Android 1.0 through 1.5 required a 2 megapixel camera with auto-focus. 204 However, with version 1.6, Android devices were permitted to omit the auto-focus 205 capability, though a (fixed-focus) camera was still required. Some apps such as 206 barcode scanners do not function as well with cameras that do not auto-focus. To 207 prevent users from having a bad experience with those apps, existing apps that 208 obtain permission to use the Camera were assumed by default to require 209 auto-focus. This allowed Google Play to filter those apps from devices that 210 lack auto-focus.</li> 211 212 <li>Android 2.2, meanwhile, allowed the microphone to be optional on some 213 devices, such as set-top boxes. Android 2.2 included a new feature ID for the 214 microphone which allows developers to filter their apps if necessary, but 215 — as with camera — apps that obtain permission to record audio are 216 assumed to require the microphone feature by default. If your app can use a 217 microphone but doesnt strictly need it, you can explicitly state that you dont 218 require it; but unless you do that, your app wont be shown to devices without 219 microphones.</li> 220 </ul> 221 222 <p>In other words, whenever Android introduces new features or changes existing 223 ones, we will always take steps to protect existing applications so that they 224 dont end up being available to devices where they wont work.</p> 225 226 <p>This is implemented, in part, using the <code>aapt</code> tool in the SDK. 227 To see which features your app explicitly requires or is implicitly assumed to 228 require, you can use the command <code>aapt dump badging</code>.</p> 229 230 <h3 id="conclusion">Conclusion</h3> 231 232 <p>The goal of Android is to create a huge installed base for developers to take 233 advantage of. One of the ways we will achieve this is through different kinds of 234 hardware running the same software environment. But we also recognize that only 235 developers know which kinds of devices their apps make sense on. Weve built in 236 tools to the SDK and set up policies and requirements to ensure that developers 237 remain in control of their apps, today and in the future. With the information 238 you just read, and the resources listed in the sidebar of this document, you 239 can publish your app with the confidence that only users who can run it will 240 see it.</p> 241 242 <p>For more information about Android device compatibility, please visit:</p> 243 244 <p style="margin-left:2em;"><a href="http://source.android.com/compatibility/index.html">http://source.android.com/compatibility/index.html</a></p> 245 246 247
