Question

Since Android introduced library projects, I’ve been converting my app into a library so that I can make several versions with appropriate tweaks (for example, a free and pro version using the same code base, but changing a few things).

I initially had trouble allowing the library project’s code access to fields in my sub-projects. In other words, my free and pro versions each had a class with a few constants in them, which the library project would use to distinguish certain features.

In the sub-project, I extended the library’s main activity and added a static initialisation block which uses reflection to change the values of fields in the library.

public class MyMainActivityProVersion extends MyMainActivity {

    public static final String TAG = Constants.APP_NAME + "/SubClass";

    static {
        try {
            ConstantsHelper.setConstants(Constants.class);
        } catch (Exception e) {
            Log.d(TAG, "--- Constants not initialised! ---");
            e.printStackTrace();
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}

In this code, ConstantsHelper is in the library, and I am providing Constants.class from my sub-project. This initialises the constants in the library project.

My approach works great, except for one particular use case. When the app hasn’t been used in a while and it is ‘stopped’ by the OS, the static fields in ConstantsHelper are forgotten.

The constants are supposed to be reset by the main activity (as shown above), but the main activity isn’t even launched because the OS resumes a different activity. The result of this is that the initialisation of the constants is forgotten and I cannot re-initialise them because the resumed activity is in the library (which has no knowledge of the sub-project).

How can I ‘tell’ other activities in the library to call code from sub-projects on resuming? Alternatively, is there a way to ensure that some code in my sub-project is called on every resume?

Answer 1

I’m afraid I never found a good answer to this question. I’ll probably continue with my terrible use of reflection and figure out some hacky workaround.

I felt I should come back and at least point out that I didn’t solve this for the benefit of others who come to this page.