App to SD functionality on Android_问答_开发者

I'm getting more and more requests about being able to use an App to SD feature that must be part of Android 2.2, but I really have no experience with it. I also don't know where to find any documentation regarding how to make my apps compatible with this feature. People have told me my apps cannot be moved to the SD card.

My mind is also telling me that this is a really bad idea for paid apps that don't have license protection of any kind.

Has anyone had any experience with this, know of any documentation, or have any tips regarding what would stop an app from being compatible with this feature?

Note: I do not use copy protection 开发者_如何学Goon my apps.

You can allow your app to be installed to the SD card using the android:installLocation manifest attribute. This can be set to preferExternal or auto, depending on whether you would like to recommend that it be installed on the SD card, or simply allow it. By default, applications cannot be installed to the SD card for backwards-compatibility reasons, so you must opt-in to this feature if you want your users to be able to use it.

From the documentation:

When your application is installed on the external storage:

There is no effect on the application performance so long as the external storage is mounted on the device.

The .apk file is saved on the external storage, but all private user data, databases, optimized .dex files, and extracted native code are saved on the internal device memory.

The unique container in which your application is stored is encrypted with a randomly generated key that can be decrypted only by the device that originally installed it. Thus, an application installed on an SD card works for only one device.

The user can move your application to the internal storage through the system settings.

Thus, you shouldn't worry about license protection too much; there is encryption built into the feature. You also generally shouldn't worry about license protection because any form of copy protection or DRM tends to be more harmful to honest users than to pirates. As long as someone is able to use your app, someone will be able to pirate it; it is well nigh impossible to create an unbreakable DRM scheme. If your app is already in internal storage, it's likely already pirated. Most users are honest, however, and will buy the app from the Market, so you won't really gain much from stopping piracy (most people who download pirated apps are those who don't have access to paid apps in the Market; it's still not available in many countries).

Anyhow, the upshot is that this should be about as secure as your app already is, and just allows users more flexibility in where to store their app. It's not enabled by default in case of bugs that cause applications that aren't expecting it to break, but it should be perfectly safe to enable.

Here you go.

And documented here.

The Android platform now allows applications to request installation onto the device's external storage media (such as the SD card), as an alternative to installation onto the device's internal memory.

Application developers can express the preferred installation location for their applications by means of a new attribute of in the manifest file, android:installLocation. The attribute supports three values: "internalOnly", "preferExternal", and"auto". At install time, the system checks the value of android:installLocation and installs the application .apk according to the preferred location, if possible. If the application has requested external installation, the system installs it into a private, encrypted partition in the external media. Once an application .apk is installed externally, the system lets the user change the storage location of the .apk and move it onto the device's internal memory if needed (and vice versa), through Manage Applications in the user settings.

By default, the system installs all applications onto the device's internal memory, except for those that explicitly request external installation. This means that the system will always install legacy applications onto internal memory, since they do not have access to theandroid:installLocation attribute. However, it is possible to configure and compile a legacy application such that it is installed internally on older versions of the platform and externally on Android 2.2 and later platforms, if necessary.

Note that requesting installation onto the device's external media is not suitable for all applications, particularly because the external media may be removable and unmounting/remounting may disrupt the user experience and system settings.

For more information about setting a preferred install location for your application, including a discussion of what types of applications should and should not request external installation, please read the App Install Location document.Install Location document.