android - handle dialogFragment buttons clicks

Question

I have Activity in my app with few fragments in it. One of these fragments has a DialogFragment, it called by button click. DialogFragment has 3 buttons - positive, negative and neutral.

public class CompanyNotConnectedToSRDialog extends DialogFragment {

    public static final String TAG = CompanyNotConnectedToSRDialog.class.getSimpleName();

    private NotConnectedDialogListener mNotConnectedDialogListener;

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        return new AlertDialog.Builder(getActivity(), R.style.DefaultAlertDialogTheme)
                .setTitle("Register")
                .setMessage("Do you really want to register?")
                .setNeutralButton("Skip", (dialog1, which) -> {
                    mNotConnectedDialogListener.onSkipBtnNotConnectedDialogPressed();
                })
                .setNegativeButton("Cancel", null)
                .setPositiveButton("Register", (dialog12, which) -> {
                    mNotConnectedDialogListener.onSendBtnNotConnectedDialogPressed();
                })
                .create();
    }


    public interface NotConnectedDialogListener {
        void onSkipBtnNotConnectedDialogPressed();
        void onSendBtnNotConnectedDialogPressed();
    }

    public void setListener(NotConnectedDialogListener listener) {
        this.mNotConnectedDialogListener = listener;
    }

As you can see I created public interface that contains two methods for my skip and register buttons (cancel button listener is null so it doesn't matter) and the Setter for this listener. Then I implemented this interface in my fragment that calls this dialogFragment, I Overrided methods and called dialogFragment like this:

if (mNotConnectedDialog == null) {
            mNotConnectedDialog = new CompanyNotConnectedToSRDialog();
            mNotConnectedDialog.setListener(this);
            mNotConnectedDialog.show(getActivity().getFragmentManager(), CompanyNotConnectedToSRDialog.TAG);
        } else {
            mNotConnectedDialog.show(mActivity.getFragmentManager(), CompanyNotConnectedToSRDialog.TAG);
            mNotConnectedDialog.setListener(this);
        }

The problem is I get NullPointerException if I press the button in my parent Fragment to show DialogFragment, rotate screen and press any button in my DialogFragment, because my listener is null.

java.lang.NullPointerException: Attempt to invoke interface method 'void com.myapp.ui.object.create.dialogs.CompanyNotConnectedToSRDialog$NotConnectedDialogListener.onSendBtnNotConnectedDialogPressed()' on a null object reference

at com.myapp.ui.object.create.dialogs.CompanyNotConnectedToSRDialog.lambda$onCreateDialog$1(CompanyNotConnectedToSRDialog.java:31)

How to handle these clicks and set listeners if this solution is wrong?

PS: please don't tell me about android:configChanges.

Answer 1

So the current solution doesn't work because when you rotate the dialog fragment is destroyed and recreated. So setListener isn't called. The solution depends on if your listener is an activity or another fragment.

If it's an activity you can override onAttach in your DialogFragment and set the listener there. If your listener is a fragment then in your OnCreateDialog method you can look the fragment up by the tag and set the listener that way. For example.

Fragment listenerFragment = getActivity().getSupportFragmentManager().findFragmentByTag(getString(R.string.your_listener_fragment_tag));

if( listenerFragment instanceOf NotConnectedDialogListener ) {
    listener = (NotConnectedDialogListener) listenerFragment;
} else {
    //Handle what to do if you don't have a listener here. Maybe dismiss the dialog. 
}