Activity And Fragment Interaction

Question

I have an Activity with multiple Fragments. I want to show a DialogFragment or open another Fragment from one of the Fragments. I know that an Activity should be the one tasked with opening Fragments so instead I have tried a couple things.

FIRST
I tried to use getActivity() and cast it so I can call a method in the Activity to show a Fragment however this creates a dependency in the Fragment with the Activity and I would like to avoid adding a dependency if possible.

SECOND
Next I tried a listener to notify the Activity that it should show a Fragment. So I created a class in the Activity to implement the listener interface. But I had problems because I had to use New MyActivity().new Listener(); and it would throw an Exception when I tried to use getSupportFragmentManager() since this instance of the Activity is not initialized.

THIRD
I then tried to have the Activity implement the listener directly which works because then I am only creating a dependency with the listener and not the Activity. However now I am getting to the point where my Activity will be implementing 2 - 4 different interfaces which is making me hesitant because it will severely reduce cohesion.

So any way I have tried I seem to be running into a brick wall and creating dependancies I'm not sure I need to be creating. Am I screwed and have to go with one of these options? If so which option would be best? Any help or suggestions are are greatly appreciated.

Answer 1

Create interface

public interface ListenFromActivity {
    void doSomethingInFragment();
}

In Activity class keep refrence of ListenFromActivity interface

 public ListenFromActivity activityListener;   

Make public method to set listener

 public void setActivityListener(ListenFromActivity activityListener) {
        this.activityListener = activityListener;
    }

Add some trigger point in activity class, here I have used user interaction

    @Override
    public void onUserInteraction() {
        super.onUserInteraction();

        if (null != activityListener) {
            activityListener.doSomethingInFragment();
        }
    }

Now in Fragment class

make your fragment implement interface class

public class SomeFragment extends Fragment implements ListenFromActivity

Android studio will prompt you to implement method of interface in fragment

 void doSomethingInFragment()
{//Add your code here 
}

Final part part listener instance to activity like this in fragment onCreate method

((ListnerActivity) getActivity()).setActivityListener(SomeFragment.this);

DONE!!. now you can call fragment method from activity.

Answer 2

Personally I would say that fragments should be thought as reusable and modular components. So in order to provide this re-usability, fragments shouldn't know much about their parent activities. But in return activities must know about fragments they are holding.

So, the first option should never be considered in my opinion for the dependency reason you mentioned causing a very highly coupled code.

About the second option, fragments may delegate any application flow or UI related decisions (showing a new fragment, deciding what to do when a fragment specific event is triggered etc..) to their parent activities. So your listeners/callbacks should be fragment specific and thus they should be declared in fragments. And the activities holding these fragments should implement these interfaces and decide what to do.

So for me the third option makes more sense. I believe that activities are more readable in terms of what they are holding and doing on specific callbacks. But yes you are right your activity might become a god object.

Maybe you can check Square's Otto project if you don't want to implement several interfaces. It's basically an event bus.