Port of the work in the following blog to the new Gradle based Android Studio build system, as per this thread on StackOverflow

As the Android Studio Gradle plugin now provides native multidex support, which effectively solves the Android 65k method limit, the main motivation for using custom class loading at runtime is now extensibility. In my particular case, I'm trying to make a plugin framework for AnkiDroid.

Therefore the main focus of this version of the project is on building the secondary jar file in a clean and modular manner, which makes it easy to update the main project without having to update the plugins. The main apk is in the app module, and the library which shows the toast is in the libraries/lib1 module with its own namespace com.example.toastlib

##STEP

1.Define interface in app main module,and implement them in libraries:lib1 module wait to generate dex file

2.Add ':libraries:lib1' in settings.gradle let libraries become a module

3.Change app.gradle from apply plugin: 'com.android.application' to apply plugin: 'com.android.library' to be dependency by libraries:lib1 (line 35)

4.Config local.properties in libraries:lib1.gradle in line 63 to get android SDK

5.Run in command line gradlew assembleExternalJar to get dex file,file name can be configured in gradle.properties by PLUGIN_NAMESPACE ,then dex file inside jar archive can be found in /libraries/lib1/build/outputs/PLUGIN_NAMESPACE.jar

6.Copy PLUGIN_NAMESPACE.jar into app' assets file

7.Change app.gradle from apply plugin: 'com.android.library' to apply plugin: 'com.android.application' and remove ':libraries:lib1' from settings.gradle