Installation of Native Libraries

An Android .apk file can contain native libraries for one or more architectures. Historically, all native libraries for the target device are extracted at .apk installation time. This would result in two copies of native libraries on the target device: a set of native libraries which are stored compressed within the .apk, and a separate set of native libraries on the Android target filesystem.

Starting with Android v6.0 (API-23), Android added an ability for native libraries to be stored uncompressed within the .apk along with the ability to load those native libraries from the .apk without requiring a separate filesystem copy of the native libraries.

Android Things requires this new mechanism; .apk files installed on Android Things will no longer have any native libraries extracted.

As a result, the .apk will be larger, because the native libraries are stored uncompressed within the .apk, but the install size will be smaller, because there isn't a second "copy" of the native libraries (one compressed in the .apk, one outside of the .apk).

On Android versions older than Android v6.0, the native libraries will continue to be extracted during .apk installation.

In order to indicate to Android v6.0 and later that native libraries do not need to be extracted, the //application/@android:extractNativeLibs attribute within AndroidManifest.xml must be set to false.

OSS Implementation Details

When AndroidManifest.xml contains an XML attribute matching //application[@android:extractNativeLibs='false'], the Xamarin.Android build system will do the following:

1. The $(AndroidStoreUncompressedFileExtensions) MSBuild property will be automatically updated to contain the .so file extension, causing native libraries to be stored uncompressed within the .apk.

2. The __XA_DSO_IN_APK environment variable will be set within the created .apk file with the value of 1, indicating to the app that native libraries should be loaded from the .apk itself instead of from the filesystem.