How can a BottomSheetDialogFragment communicate with its host fragment?

Question

I have a button in my fragment which opens a BottomSheetDialogFragment. I want to notify the host fragment if the user selected an item on the BottomSheetDialogFragment. In order to achieve this, I have made an interface in my BottomSheetDialogFragment. However, that interface only communicates with the host activity, not the fragment. How can I send the information from the dialog to the fragment?

This is my interface:

public interface BottomSheetListener {
        void onButtonClicked(int index);
    }

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        try {
            mListener = (BottomSheetListener) context;
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString() + " must implement BottomSheetListener");
        }
    }

score 4 · Accepted Answer · answered Jan 19 '21 at 18:09

getParentFragment will return the parent fragment, if the current fragment is attached to a fragment else it will return null if it is attached directly to an Activity

@Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        try {
            mListener = (BottomSheetListener) getParentFragment();
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString() + " must implement BottomSheetListener");
        }
    }

score 2 · Answer 2 · answered Jan 19 '21 at 19:24

When you use a lot of fragments, nested fragments or dialogfragments it becomes messy for communicate between them. I am suggesting to use ViewModel with LiveData for passing and updating data.

first add this to build gradle :

implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

then create ViewModel class :

public class YourViewModel extends AndroidViewModel {

private MutableLiveData<Integer> yourMutableLiveData=new MutableLiveData<>();

public YourViewModel(@NonNull Application application) {
    super(application);
}

public MutableLiveData<Integer> getYourMutableLiveData() {
    return yourMutableLiveData;
}

}

This the fragment you want set value :

   public class FragmentA extends Fragment{

        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            YourViewModel yourViewModel =new ViewModelProvider(getActivity()).get(YourViewModel.class);

            yourViewModel.getYourMutableLiveData().setValue(0);
        }
    }

And this is the fragment you want to get value when updated :

 public class FragmentB extends Fragment{

        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            YourViewModel yourViewModel =new ViewModelProvider(getActivity()).get(YourViewModel.class);

            yourViewModel.getYourMutableLiveData().observe(getViewLifecycleOwner(), new Observer<Integer>() {
                @Override
                public void onChanged(Integer integer) {

                }
            });
        }
    }

It can work on dialog fragment as well as I tested.

Notes : -Do not pass context or any view into view model.

-Remember that onActivityCreated comes after onCreateView.

-Do not set this key to

 YourViewModel yourViewModel =new ViewModelProvider(this).get(YourViewModel.class);

in fragment if you want to pass data fragment to fragment but you can pass in activity.

-You can set more than one observer to the data.

Please tell me if there is any problem. Dealing with ViewModel might be problematic on your first try but it's very easy to use when you get used to it and definitely worth your trouble. — Eray Agdoğan, Jan 20 '21 at 15:34

How can a BottomSheetDialogFragment communicate with its host fragment?

2 Answers2