1 page.title=Support Library 2 page.metaDescription=The Android Support Library offers backward-compatible versions of a number of features that are not built into the framework. 3 4 @jd:body 5 6 <div id="qv-wrapper"> 7 <div id="qv"> 8 9 <h2>In this document</h2> 10 <ol> 11 <li><a href="#overview">Overview</a></li> 12 <li><a href="#backward">Backward Compatibility</a></li> 13 <li><a href="#layout-patterns">Support for General Layout Patterns</a></li> 14 <li><a href="#form-factors">Support for Different Form Factors</a></li> 15 <li><a href="#utils">General Utilities</a></li> 16 </ol> 17 18 <h2>See also</h2> 19 <ol> 20 <li><a href="{@docRoot}topic/libraries/support-library/features.html"> 21 Support Library Features</a></li> 22 <li><a href="{@docRoot}topic/libraries/support-library/setup.html"> 23 Support Library Setup</a></li> 24 <li><a href="{@docRoot}topic/libraries/support-library/revisions.html"> 25 Support Library Revision History</a></li> 26 27 </ol> 28 29 </div> 30 </div> 31 32 <p> 33 The Android Support Library offers a number of features that are not built 34 into the framework. These libraries offer backward-compatible versions of 35 new features, provide useful UI elements that are not included in the 36 framework, and provide a range of utilities that apps can draw on. 37 </p> 38 39 <h2 id="overview">Overview</h2> 40 41 <p> 42 In many cases, a feature may be valuable to many app developers, but not 43 appropriate to include in the Android framework itself. For example, an app 44 might only need a feature for specialized use cases, such as to smooth the 45 transition between different versions of the Android system. 46 </p> 47 48 <p> 49 To address these situations, the Android SDK includes several libraries 50 collectively called the <em>Android Support Library</em>. App developers 51 can include any of these libraries if they want to incorporate the 52 library functionality into their apps. 53 </p> 54 55 <p> 56 Support libraries provide a range of different features: 57 </p> 58 59 <ul> 60 <li> 61 <a href="#backward">Backward-compatible</a> versions of framework 62 components. 63 </li> 64 65 <li>UI elements to implement the recommended Android <a href= 66 "#layout-patterns">layout patterns</a>. 67 </li> 68 69 <li>Support for different <a href="#form-factors">form factors</a>. 70 </li> 71 72 <li>Miscellaneous <a href="#utils">utility</a> functions. 73 </li> 74 </ul> 75 76 <h2 id="backward">Backward Compatibility</h2> 77 78 <div class="figure" style="width:300px"> 79 <img src="{@docRoot}images/tools/support-library/appbar-kitkat.png" 80 srcset="{@docRoot}images/tools/support-library/appbar-kitkat.png 1x, 81 {@docRoot}images/tools/support-library/appbar-kitkat_2x.png 2x" 82 alt="" width="300"> 83 <p class="img-caption"> 84 <strong>Figure 1.</strong> Because this app uses support library UI 85 elements its interface incorporates material design principles, even though 86 it is running on Android 4.4, which does not include native support for 87 material design. 88 </p> 89 </div> 90 91 <p> 92 Support libraries allow apps running on older versions of the Android 93 platform to support features made available on newer versions of the 94 platform. For example, an app running on a version of Android lower than 5.0 95 (API level 21) that relies on framework classes cannot display 96 material-design elements, as that version of the Android framework doesn't 97 support material design. However, if the app incorporates the Support 98 Library's <a href="{@docRoot}tools/support-library/features.html">appcompat 99 library</a>, the app has access to many of the features available in API 100 level 21, including support for material design. As a result, your app can 101 deliver a more consistent experience across a broader range of platform 102 versions. 103 </p> 104 105 106 <p> 107 In some cases, the support library version of a class depends as much as 108 possible on the functionality that the framework provides. In these cases, 109 if an app calls one of the support class's methods, the support library's 110 behavior depends on what version of Android the app is running on. If the 111 framework provides the necessary functionality, the support library calls on 112 the framework to perform the task. If the app is running on an earlier 113 version of Android, and the framework doesn't expose the needed 114 functionality, the support library may try to provide the functionality 115 itself, or may act as a no-op. In either case, the app generally doesn't 116 need to check what version of Android it's running on; instead, the app 117 can rely on the support library to do those checks and choose appropriate 118 behavior. Generally, classes whose names end in 119 <code>Compat</code> (like {@link android.support.v4.app.ActivityCompat}) 120 behave this way. 121 </p> 122 123 <p> 124 In other cases, the support library class provides a complete, standalone 125 version of a framework class that does not rely on the availability of 126 any framework APIs. These 127 methods provide consistent behavior across all supported platforms. 128 </p> 129 130 <p> 131 In either case, the app does not need to check the system version at run 132 time. The app can rely on the support library class to do the appropriate 133 system checks, and modify its behavior as necessary. 134 </p> 135 136 <h2 id="layout-patterns">Support for General Layout Patterns</h2> 137 138 <p> 139 Support libraries provide user interface elements not offered by 140 the Android framework. For example, the Android Support Library offers additional 141 layout classes, like {@link android.support.v4.widget.DrawerLayout}. These 142 classes follow recommended Android design practices; for example, the Design 143 Library follows the principles of material design in a way that works across 144 many versions of Android. 145 </p> 146 147 <p> 148 By using these support library classes, you can avoid having to reinvent the 149 wheel; if your app has a particular user interface requirement, you can draw 150 on existing code, which provides a user interface that users will already be 151 familiar with. These elements also help you build an app that looks and feels 152 like a part of the Android ecosystem. For example, many apps need to display 153 arbitrarily long lists of elements, and need to be able to quickly and 154 efficiently reuse those elements as the list changes; this might be a list of 155 emails, contacts, music albums, and so on. Those apps can use the support 156 library {@link android.support.v7.widget.RecyclerView} widget to display the 157 list. This saves the app developer from having to develop the list from 158 scratch, and also ensures that the user will see a list that looks and 159 behaves like lists in other apps. 160 </p> 161 162 <h2 id="form-factors">Support for Different Form Factors</h2> 163 164 <p> 165 The Android SDK provides libraries for a number of different form factors, 166 such as TV and wearables. An app can depend on the appropriate support 167 library to provide functionality across a wide range of platform versions, 168 and can provide content on external screens, speakers, and other destination 169 devices. 170 </p> 171 172 <h2 id="utils">General Utilities</h2> 173 174 <p> 175 The Android Support Library provides backward-compatible utility functions. 176 Apps can use these utility functions to provide an appropriate user 177 experience across a wide range of Android system versions. For example, 178 support library permission methods behave appropriately depending on what 179 platform version your app is running on. If the platform supports the 180 runtime permissions model, these methods request the appropriate permission 181 from the user; on platform versions that do not support the runtime 182 permissions model, the methods check whether the appropriate permission was 183 granted at install time. 184 </p> 185
