Software design consulting needed (Android Library Project)

• I have an App with my main Activity ("MainActivity")
• I have a View in a "Android Project Library". I would like to use this view in several Apps, thats why I added this view in a library.
• I can use the view from my App

But now comes the problem.

I would like to interact with my Apps MainActivity from my view.

If the view would be in the app insteed of library I would simply call...

(MainActivity)context.myfunction()

... in my view.

But in case of the library, my view doesn't know about the MainActivity, because its out of the project-scope.

How can I interact with the Activity from my view, which is placed in a library ? Any hints ?