Interface communication from fragment to activity issue

Question

I've recently tried to use an interface for fragment-activity communication. The idea is that when a button is pressed in a fragment, it retrieves data from an EditText in the same fragment, it then sends the string to the MainActivty - this controls all my fragments - which then starts another fragment and delivers the string to this fragment for use later, however, I'm having trouble initially setting up the first interface which sends the data. Unfortunately nothing happens, and I cannot therefore get to the next fragment which should be displayed. Additionally I have tried using getActivity() but it cannot find the associated method within the fragment, leading me to believe that the fragments somehow aren't directly connected to MainActivity (I've only just grasped basics of Java and a little of Android, just learning.)

I've listed the relevant information below, thanks for the assistance!

Fragment

public class CreateWorkoutFragment extends Fragment implements OnClickListener {

View rootViewCreateWorkoutFragment;

EditText editTextWorkoutName;

// Using an ImageView for custom button
ImageView buttonNext;

String valueCreateWorkoutEditText;

OnDataPass dataPasser;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    rootViewCreateWorkoutFragment = inflater.inflate(R.layout.fragment_create_workout, container, false);

    buttonNext = (ImageView) rootViewCreateWorkoutFragment.findViewById(R.id.button_workout_name_next);

    editTextWorkoutName = (EditText) rootViewCreateWorkoutFragment.findViewById(R.id.edit_text_workout_name);

    buttonNext.setOnClickListener(this);

    return rootViewCreateWorkoutFragment;
}

public interface OnDataPass {
    public void onDataPass(String data);
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    dataPasser = (OnDataPass) activity;
}

public void passData(String data) {
    dataPasser.onDataPass(data);
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.button_workout_name_next:
            valueCreateWorkoutEditText = editTextWorkoutName.getText().toString();
            passData(valueCreateWorkoutEditText);
            break;
    }
}
}

Main Activity

public class MainActivity extends FragmentActivity implements OnClickListener, CreateWorkoutFragment.OnDataPass {

ImageView buttonCreate;

Fragment newFragment;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setTheme(R.style.AppThemeBlue);
    setContentView(R.layout.activity_main);

    buttonCreate = (ImageView) findViewById(R.id.create_foreground);

    buttonCreate.setOnClickListener(this);

    FragmentManager fragManager = getSupportFragmentManager();
    FragmentTransaction tranManager = fragManager.beginTransaction();
    CreateWorkoutFragment createWorkoutFrag = new CreateWorkoutFragment();

    // fragment_change is just the area in XML where fragments switch
    tranManager.add(R.id.fragment_change, createWorkoutFrag);
    tranManager.commit();

    newFragment = null;
}

@Override
public void onDataPass(String data) {
    // CreateFragment is not to be confused with CreateWorkoutFragment
    // CreateFragment is the fragment I'm trying to start when any strings
    // are obtained from CreateWorkoutFragment
    newFragment = new CreateFragment();
}

@Override
public void onClick(View v) {

    switch (v.getId()) {
    // create_foreground is just an ImageView used as a button
    // Additionaly, other buttons are used to create other fragments,
    // I've cut them out currently as they are not nessesary which is
    // why CreateWorkoutFragment is only button and default currently
    case R.id.create_foreground:
        newFragment = new CreateWorkoutFragment();
        break;
    default:
        newFragment = new CreateWorkoutFragment();
    }

FragmentTransaction tranManager = getSupportFragmentManager().beginTransaction();
    tranManager.replace(R.id.fragment_change, newFragment);
    tranManager.addToBackStack(null);
    tranManager.commit();
}
}

Sorry the code isn't exactly tidy, however, it was the most relevant code cut out from a large class. As I said, I have tried other methods yet cannot get any response from MainActivity either way. Thanks in advance!

Just before I posted: Got the app to write logcat messages to me, it manages to pass the data when the button is clicked - at least I think, and is something to do with the fragment not starting! At MainActivity>onDataPass()>new Fragment = new CreateFragment() Any ideas? As mentioned before, other buttons do exist and manage to change the fragment. However, were cutout to reduce amount of code posted.

Answer 1

getActivity() but it cannot find the associated method within the fragment

This is because getActivity() returns an Activity, not a MainActivity which is your custom subclass. You can easily fix this with a cast. For example, in your fragment, you can do this:

OnDataPass main = (OnDataPass) getActivity();
main.onDataPass(message);

Since such a cast is required, the interface seems to get in the way in my opinion. You can just as easily cast directly to MainActivity:

MainActivity main = (MainActivity) getActivity();
main.onDataPass(message);