Beginning with API Level 8, you can allow your application to be installed on the external storage (for example, the device's SD card). This is an optional feature you can declare for your application with the {@code android:installLocation} manifest attribute. If you do not declare this attribute, your application will be installed on the internal storage only and it cannot be moved to the external storage.
To allow the system to install your application on the external storage, modify your
manifest file to include the {@code
android:installLocation} attribute in the <manifest> element,
with a value of either "{@code preferExternal}" or "{@code auto}". For example:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
android:installLocation="preferExternal"
... >
If you declare "{@code preferExternal}", you request that your application be installed on the external storage, but the system does not guarantee that your application will be installed on the external storage. If the external storage is full, the system will install it on the internal storage. The user can also move your application between the two locations.
If you declare "{@code auto}", you indicate that your application may be installed on the external storage, but you don't have a preference of install location. The system will decide where to install your application based on several factors. The user can also move your application between the two locations.
When your application is installed on the external storage:
Warning: When the user enables USB mass storage to share files with a computer or unmounts the SD card via the system settings, the external storage is unmounted from the device and all applications running on the external storage are immediately killed.
The ability for your application to install on the external storage is a feature available only on devices running API Level 8 (Android 2.2) or greater. Existing applications that were built prior to API Level 8 will always install on the internal storage and cannot be moved to the external storage (even on devices with API Level 8). However, if your application is designed to support an API Level lower than 8, you can choose to support this feature for devices with API Level 8 or greater and still be compatible with devices using an API Level lower than 8.
To allow installation on external storage and remain compatible with versions lower than API Level 8:
<manifest>
element.When your application is installed on a device with an API Level lower than 8, the {@code android:installLocation} attribute is ignored and the application is installed on the internal storage.
Caution: Although XML markup such as this will be ignored by older platforms, you must be careful not to use programming APIs introduced in API Level 8 while your {@code minSdkVersion} is less than "8", unless you perform the work necessary to provide backward compatibility in your code. For information about building backward compatibility in your application code, see the Backward Compatibility article.
When the user enables USB mass storage to share files with their computer (or otherwise unmounts or removes the external storage), any application installed on the external storage and currently running is killed. The system effectively becomes unaware of the application until mass storage is disabled and the external storage is remounted on the device. Besides killing the application and making it unavailable to the user, this can break some types of applications in a more serious way. In order for your application to consistently behave as expected, you should not allow your application to be installed on the external storage if it uses any of the following features, due to the cited consequences when the external storage is unmounted:
If your application uses any of the features listed above, you should not allow your application to install on external storage. By default, the system will not allow your application to install on the external storage, so you don't need to worry about your existing applications. However, if you're certain that your application should never be installed on the external storage, then you should make this clear by declaring {@code android:installLocation} with a value of "{@code internalOnly}". Though this does not change the default behavior, it explicitly states that your application should only be installed on the internal storage and serves as a reminder to you and other developers that this decision has been made.
In simple terms, anything that does not use the features listed in the previous section are safe when installed on external storage. Large games are more commonly the types of applications that should allow installation on external storage, because games don't typically provide additional services when innactive. When external storage becomes unavailable and a game process is killed, there should be no visible effect when the storage becomes available again and the user restarts the game (assuming that the game properly saved its state during the normal Activity lifecycle).
If your application requires several megabytes for the APK file, you should carefully consider whether to enable the application to install on the external storage so that users can preserve space on their internal storage.