How to Implement Communication Between a Fragment and a Custom Cursor Adapter?

Interfacing Fragment and Adapter

Introduction:
Creating a communication channel between a fragment and a custom cursor adapter can facilitate seamless data exchange and event handling between these components.

Problem:
A fragment contains a ListView associated with a cursor adapter. The adapter features a button in each list row with an onClick listener. The goal is to notify the fragment when this button is pressed.

Solution:

1. Define an Interface in the Adapter:

   • Create an AdapterInterface within the adapter class with a method buttonPressed().

2. Implement the Interface in the Fragment:

   • In the fragment class, implement the AdapterInterface and override the buttonPressed() method.

3. Pass the Fragment as an Argument to the Adapter:

   • Add a constructor to the adapter class that accepts an AdapterInterface object.
   • When instantiating the adapter, pass the fragment (which implements AdapterInterface) as an argument.

4. Invoke the Interface from the Adapter's OnClickListener:

   • Inside the adapter's bindView() method, set the onClick listener for the button.
   • Within the listener, call the buttonPressed() method of the passed-in fragment.

Example Code:

public class MyListAdapter extends CursorAdapter {

    public interface AdapterInterface {
        public void buttonPressed();
    }

    private AdapterInterface buttonListener;

    public MyListAdapter (Context context, Cursor c, int flags, AdapterInterface buttonListener) {
        super(context,c,flags);
        this.buttonListener = buttonListener;
    }

    @Override
    public void bindView(final View view, final Context context, final Cursor cursor) {
        ViewHolder holder = (ViewHolder) view.getTag();

        ...

        holder.button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                buttonListener.buttonPressed();
            }
        });
    }
}

public MyListFragment extends Fragment implements AdapterInterface {

    @Override
    public void buttonPressed() {
        // some action
    }
}

5. Usage:

   • Create an instance of the adapter, passing the fragment as an argument:

     MyListAdapter adapter = new MyListAdapter (getActivity(), myCursor, myFlags, this);

6. Caution for Orientation Changes:

   • Note that fragment recreation on orientation changes can lead to a lingering adapter reference to a non-existent fragment. To prevent this, consider recreating the adapter as well.

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