Android, Best way to provide app specific constants in a library project?

Question

I am creating a library project for a number of android apps. The apps all have some common functionality that I wish to include in the library project but the library project f

Answer 1

I don't know of a great schema to do that but it would certainly work this way:

define some base class in your library

// class, enum or whatever you want it to be. 
class BaseConstants {
    // use some real singleton instead
    public static final BaseConstants instance = new BaseConstants();

    // define those values - sadly static inheritance does not work
    private static final int APP_ID = 0;
    private static final int CURRENT_APP_ID_KEY = 24;

    // so we have to do that via methods
    protected int getAppId() {
        return APP_ID;
    }
    protected int getAppIdKey() {
        return CURRENT_APP_ID_KEY;
    }
}

let each Activity that wants something custom implement that

class App1Constants extends BaseConstants {
    public static final App1Constants instance = new App1Constants();

    private final static int APP_ID = 1;

    // want a different APP_ID here.
    protected int getAppId() {
        return APP_ID;
    }

    // getAppIdKey not implemented here, uses default
}

Use that class as context to the constants for your library

class Library {
    public static long getCurrentAppId(Context context, BaseConstants settings) {
        return getLongPreference(context, settings.getAppIdKey(), settings.getAppId());
    }
}

Activities would be like so

class myActivity extends Activity {
    // each Activity can implement it's own constants class and overwrite only some values
    private static final BaseConstants CONSTANTS = App1Constants.instance;

    private void whatever() {
        long appId = Library.getCurrentAppId(this, CONSTANTS);
    }
}

class myActivity2 extends Activity {
    // or could just use the default ones
    private static final BaseConstants CONSTANTS = BaseConstants.instance;

    private void whatever() {
        long appId = Library.getCurrentAppId(this, CONSTANTS);
    }
}

That schema is kind of ugly but it would work at least