Drag and Drop view between two Fragments

问题

I'm currently trying to implement Drag and Drop between two Fragments. I already added them both to my Activity like this

    FragmentManager fm = getFragmentManager();
    FragmentTransaction ft = fm.beginTransaction();
    ft.add(R.id.leftContainer, new MainActivityFragment());
    ft.add(R.id.rightContainer, new CartFragment());
    ft.commit();

I have several CardViews in my MainActivityFragment. I'd like to drag them over to a ListView in my CartFragment. Then I'd add a new item to this ListView after the CardView has been dropped.

I've added this code in my MainActivityFragment so far

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

    firstProduct = (LinearLayout) currentView.findViewById(R.id.firstProduct);

    firstProduct.setOnTouchListener(new MyTouchListener());

    return currentView;
}

private final class MyTouchListener implements View.OnTouchListener {
    public boolean onTouch(View view, MotionEvent motionEvent) {
        if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
            ClipData data = ClipData.newPlainText("", "");
            View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
            view.startDrag(data, shadowBuilder, view, 0);
            return true;
        } else {
            return false;
        }
    }
}

class MyDragListener implements View.OnDragListener {
    Drawable enterShape = getResources().getDrawable(R.drawable.drag_overlay);

    @Override
    public boolean onDrag(View v, DragEvent event) {
        int action = event.getAction();
        switch (event.getAction()) {
            case DragEvent.ACTION_DRAG_STARTED:
                // do nothing
                v.setBackgroundDrawable(enterShape);

                break;
            case DragEvent.ACTION_DRAG_ENTERED:
                break;
            case DragEvent.ACTION_DRAG_EXITED:
                break;
            case DragEvent.ACTION_DROP:
                // Dropped, reassign View to ViewGroup
                View view = (View) event.getLocalState();

                view.setVisibility(View.VISIBLE);
                break;
            case DragEvent.ACTION_DRAG_ENDED:
            default:
                break;
        }
        return true;
    }
}

If the CardView I want to drag and the ListView I want to drop it on would be in the same View, I'd just just say

        listView.setOnDragListener(new MyDragListener());

But since I can't access the ListView because it's in a different Fragment I have no idea how to do this.

I've already seen this thread drag-and-drop-between-two-fragments

but still I can't figure it out.

Hope I described it well enough, thanks in advance!

回答1:

I came across this same issue and found an excellent way to implement this using abstract classes. You can write your abstract class:

public abstract class SomeFragment extends Fragment{
    //add your touch and drag listeners here
}

And then have your two classes that originally extended Fragment extend your abstract class instead:

public class MainActivityFragment extends SomeFragment{

}

Since your listeners were defined in your abstract class, these assignments would be allowed:

public class CartFragment extends SomeFragment{
    listView.setOnDragListener(new MyDragListener());
}

And, your subclasses like CartFragment will still be of type Fragment because SomeFragment is of type Fragment.

回答2:

The onDrag method must be implemented inside that fragment that will be accepting the DragEvent.Action_Drop case, and then you set this method on to the view(Fragment view) that you want to accept the dropped view

来源：https://stackoverflow.com/questions/29283904/drag-and-drop-view-between-two-fragments