java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference

Question

I always get an Error in my Android Project.

java.lang.NullPointerException: Attempt to invoke virtual method \'android.view.View android.app.Activi

Answer 1

In addition to what @Selvin pointed out, it looks like this:

Button add = (Button) activity.findViewById(R.id.add);

...should be changed to this:

Button add = (Button) rootView.findViewById(R.id.add);