1 page.title=App Install Location 2 page.tags="sdcard","external" 3 @jd:body 4 5 6 <div id="qv-wrapper"> 7 <div id="qv"> 8 9 <h2>Quickview</h2> 10 <ul> 11 <li>You can allow your application to install on the device's external storage.</li> 12 <li>Some types of applications should <strong>not</strong> allow installation on the external 13 storage.</li> 14 <li>Installing on the external storage is ideal for large applications that are not tightly 15 integrated with the system (most commonly, games).</li> 16 </ul> 17 18 <h2>In this document</h2> 19 <ol> 20 <li><a href="#Compatiblity">Backward Compatibility</a></li> 21 <li><a href="#ShouldNot">Applications That Should NOT Install on External Storage</a></li> 22 <li><a href="#Should">Applications That Should Install on External Storage</a></li> 23 </ol> 24 25 <h2>See also</h2> 26 <ol> 27 <li><code><a href="{@docRoot}guide/topics/manifest/manifest-element.html"> 28 <manifest></a></code></li> 29 </ol> 30 31 </div> 32 </div> 33 34 <p>Beginning with API Level 8, you can allow your application to be installed on the 35 external storage (for example, the device's SD card). This is an optional feature you can declare 36 for your application with the <a 37 href="{@docRoot}guide/topics/manifest/manifest-element.html#install">{@code 38 android:installLocation}</a> manifest attribute. If you do 39 <em>not</em> declare this attribute, your application will be installed on the internal storage 40 only and it cannot be moved to the external storage.</p> 41 42 <p>To allow the system to install your application on the external storage, modify your 43 manifest file to include the <a 44 href="{@docRoot}guide/topics/manifest/manifest-element.html#install">{@code 45 android:installLocation}</a> attribute in the <code><a 46 href="{@docRoot}guide/topics/manifest/manifest-element.html"><manifest></a></code> element, 47 with a value of either "{@code preferExternal}" or "{@code auto}". For example:</p> 48 49 <pre> 50 <manifest xmlns:android="http://schemas.android.com/apk/res/android" 51 android:installLocation="preferExternal" 52 ... > 53 </pre> 54 55 <p>If you declare "{@code preferExternal}", you request that your application be installed on the 56 external storage, but the system does not guarantee that your application will be installed on 57 the external storage. If the external storage is full, the system will install it on the internal 58 storage. The user can also move your application between the two locations.</p> 59 60 <p>If you declare "{@code auto}", you indicate that your application may be installed on the 61 external storage, but you don't have a preference of install location. The system will 62 decide where to install your application based on several factors. The user can also move your 63 application between the two locations.</p> 64 65 <p>When your application is installed on the external storage:</p> 66 <ul> 67 <li>There is no effect on the application performance so long 68 as the external storage is mounted on the device.</li> 69 <li>The {@code .apk} file is saved on the external storage, but all private user data, 70 databases, optimized {@code .dex} files, and extracted native code are saved on the 71 internal device memory.</li> 72 <li>The unique container in which your application is stored is encrypted with a randomly 73 generated key that can be decrypted only by the device that originally installed it. Thus, an 74 application installed on an SD card works for only one device.</li> 75 <li>The user can move your application to the internal storage through the system settings.</li> 76 </ul> 77 78 <p class="warning"><strong>Warning:</strong> When the user enables USB mass storage to share files 79 with a computer or unmounts the SD card via the system settings, the external storage is unmounted 80 from the device and all applications running on the external storage are immediately killed.</p> 81 82 83 84 <h2 id="Compatiblity">Backward Compatibility</h2> 85 86 <p>The ability for your application to install on the external storage is a feature available only 87 on devices running API Level 8 (Android 2.2) or greater. Existing applications that were built prior 88 to API Level 8 will always install on the internal storage and cannot be moved to the external 89 storage (even on devices with API Level 8). However, if your application is designed to support an 90 API Level <em>lower than</em> 8, you can choose to support this feature for devices with API Level 8 91 or greater and still be compatible with devices using an API Level lower than 8.</p> 92 93 <p>To allow installation on external storage and remain compatible with versions lower than API 94 Level 8:</p> 95 <ol> 96 <li>Include the {@code android:installLocation} attribute with a value of "{@code auto}" or 97 "{@code preferExternal}" in the <code><a 98 href="{@docRoot}guide/topics/manifest/uses-sdk-element.html"><manifest></a></code> 99 element.</li> 100 <li>Leave your {@code android:minSdkVersion} attribute as is (something <em>less 101 than</em> "8") and be certain that your application code uses only APIs compatible with that 102 level.</li> 103 <li>In order to compile your application, change your build target to API Level 8. This is 104 necessary because older Android libraries don't understand the {@code android:installLocation} 105 attribute and will not compile your application when it's present.</li> 106 </ol> 107 108 <p>When your application is installed on a device with an API Level lower than 8, the {@code 109 android:installLocation} attribute is ignored and the application is installed on the internal 110 storage.</p> 111 112 <p class="caution"><strong>Caution:</strong> Although XML markup such as this will be ignored by 113 older platforms, you must be careful not to use programming APIs introduced in API Level 8 114 while your {@code minSdkVersion} is less than "8", unless you perform the work necessary to 115 provide backward compatibility in your code.</p> 116 117 118 119 <h2 id="ShouldNot">Applications That Should NOT Install on External Storage</h2> 120 121 <p>When the user enables USB mass storage to share files with their computer (or otherwise 122 unmounts or removes the external storage), any application 123 installed on the external storage and currently running is killed. The system effectively becomes 124 unaware of the application until mass storage is disabled and the external storage is 125 remounted on the device. Besides killing the application and making it unavailable to the user, 126 this can break some types of applications in a more serious way. In order for your application to 127 consistently behave as expected, you <strong>should not</strong> allow your application to be 128 installed on the external storage if it uses any of the following features, due to the cited 129 consequences when the external storage is unmounted:</p> 130 131 <dl> 132 <dt>Services</dt> 133 <dd>Your running {@link android.app.Service} will be killed and will not be restarted when 134 external storage is remounted. You can, however, register for the {@link 135 android.content.Intent#ACTION_EXTERNAL_APPLICATIONS_AVAILABLE} broadcast Intent, which will notify 136 your application when applications installed on external storage have become available to the 137 system again. At which time, you can restart your Service.</dd> 138 <dt>Alarm Services</dt> 139 <dd>Your alarms registered with {@link android.app.AlarmManager} will be cancelled. You must 140 manually re-register any alarms when external storage is remounted.</dd> 141 <dt>Input Method Engines</dt> 142 <dd>Your <a href="{@docRoot}guide/topics/text/creating-input-method.html">IME</a> will be 143 replaced by the default IME. When external storage is remounted, the user can open system settings 144 to enable your IME again.</dd> 145 <dt>Live Wallpapers</dt> 146 <dd>Your running <a href="http://android-developers.blogspot.com/2010/02/live-wallpapers.html">Live Wallpaper</a> 147 will be replaced by the default Live Wallpaper. When external storage is remounted, the user can 148 select your Live Wallpaper again.</dd> 149 <dt>App Widgets</dt> 150 <dd>Your <a href="{@docRoot}guide/topics/appwidgets/index.html">App Widget</a> will be removed 151 from the home screen. When external storage is remounted, your App Widget will <em>not</em> be 152 available for the user to select until the system resets the home application (usually not until a 153 system reboot).</dd> 154 <dt>Account Managers</dt> 155 <dd>Your accounts created with {@link android.accounts.AccountManager} will disappear until 156 external storage is remounted.</dd> 157 <dt>Sync Adapters</dt> 158 <dd>Your {@link android.content.AbstractThreadedSyncAdapter} and all its sync functionality will 159 not work until external storage is remounted.</dd> 160 <dt>Device Administrators</dt> 161 <dd>Your {@link android.app.admin.DeviceAdminReceiver} and all its admin capabilities will 162 be disabled, which can have unforeseeable consequences for the device functionality, which may 163 persist after external storage is remounted.</dd> 164 <dt>Broadcast Receivers listening for "boot completed"</dt> 165 <dd>The system delivers the {@link android.content.Intent#ACTION_BOOT_COMPLETED} broadcast 166 before the external storage is mounted to the device. If your application is installed on the 167 external storage, it can never receive this broadcast.</dd> 168 </dl> 169 170 <p>If your application uses any of the features listed above, you <strong>should not</strong> allow 171 your application to install on external storage. By default, the system <em>will not</em> allow your 172 application to install on the external storage, so you don't need to worry about your existing 173 applications. However, if you're certain that your application should never be installed on the 174 external storage, then you should make this clear by declaring <a 175 href="{@docRoot}guide/topics/manifest/manifest-element.html#install">{@code 176 android:installLocation}</a> with a value of "{@code internalOnly}". Though this does not 177 change the default behavior, it explicitly states that your application should only be installed 178 on the internal storage and serves as a reminder to you and other developers that this decision has 179 been made.</p> 180 181 182 <h2 id="Should">Applications That Should Install on External Storage</h2> 183 184 <p>In simple terms, anything that does not use the features listed in the previous section 185 are safe when installed on external storage. Large games are more commonly the types of 186 applications that should allow installation on external storage, because games don't typically 187 provide additional services when inactive. When external storage becomes unavailable and a game 188 process is killed, there should be no visible effect when the storage becomes available again and 189 the user restarts the game (assuming that the game properly saved its state during the normal 190 <a href="{@docRoot}guide/components/activities.html#Lifecycle">Activity lifecycle</a>).</p> 191 192 <p>If your application requires several megabytes for the APK file, you should 193 carefully consider whether to enable the application to install on the external storage so that 194 users can preserve space on their internal storage.</p> 195 196
