I want my button to call a method in a fragment

Question

So I have (WorkoutList Activity) -> (WorkoutList Fragment) -> (ExerciseList Fragment) -> (addExercise Fragment)

Theres a button in AddExercise, and I want it to invoke a method in ExerciseList

The problem is that with the current set-up I'm getting `Attempt to invoke virtual method

void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

XML for AddExercise button:

<Button
    android:id="@+id/add_exercise_button"
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:text="@string/add_workout_message_done"
    android:layout_weight="0"
    android:onClick="addExerciseDone"
    />

code snippet of ExerciseList inside the OnCreateView method:

     View rootView = inflater.inflate(R.layout.fragment_exercise_list, container, false);
    Button AddExerciseDoneButton = (Button) getActivity().findViewById(R.id.add_exercise_button);
    AddExerciseDoneButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            addExerciseDone(v);
        }
    });

Note: This is in response to chinmay's suggestion** I have the viewroot set to the ExerciseList's XML file so I can make my adapter to display my listview, so I'm not sure how return the view I created so I can reference the buttons. For example, I made

final View tmpView = inflater.inflate(R.layout.fragment_add_exercise, container, false);

    Button AddExerciseDoneButton = (Button) tmpView.findViewById(R.id.add_exercise_button);

Answer 1

you are getting NullPointerException because your reference to AddExerciseDoneButton is not a valid one. You haven't specified any layout which has the button ID - R.id.add_exercise_button and when you are trying to use that button it will give NullPointer

instead your onCreateView should look like

public static class ExampleFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.example_fragment, container, false);
    }
}

make your view refer to the view which onCreateView is returning it will get the button ID

for reference : http://developer.android.com/guide/components/fragments.html

you are doing this

View rootView = inflater.inflate(R.layout.fragment_exercise_list, container, false);
    Button AddExerciseDoneButton = (Button) getActivity().findViewById(R.id.add_exercise_button);

instead of that to this

     View rootView = inflater.inflate(R.layout.fragment_exercise_list, container, false);
        Button AddExerciseDoneButton = (Button) 
rootView.findViewById(R.id.add_exercise_button);