When developing Apps for the Android OS you might end up in the situation where you have common Activities or Services which could be reused in multiple Apps with just a little modification. As you don’t want to copy these classes into every single project – which would lead to a hardly maintainable code – you would seek a way to reference the source of these classes from multiple projects. For non-android applications an approach for this problem would be to break up the code into multiple libraries so that the required functionality can be referenced from multiple projects. As long as you are not interacting with external resources this attempt is also possible in Android projects (build a jar and reference it from the projects). But if you are using external resources these classes can’t be used within a library. This is caused by the fact that the Android SDK won’t generate matching ids within the “R” class for external resources which are included in a referenced jar file. In this post I want to show you different solutions for this problem which can avoid the necessity to copy the source code into the projects.