ItemTouchHelper.SimpleCallback onMove() is not triggered

Question

I want to realize drag and drop in my RecyclerView. As I found out, the best way to implement this is by attaching an ItemTouchHelper to the RecyclerView.

onSwiped() works fine, but onMove() is never triggered.

This is what I do:

EditIngredientsRecyclerViewAdapter premixableIngredientsAdapter = new EditIngredientsRecyclerViewAdapter(this, typeOfComponents);
        GridLayoutManager gridLayoutManager1 = new GridLayoutManager(getContext(), 1);
        recyclerView.setAdapter(premixableIngredientsAdapter);
        recyclerView.setLayoutManager(gridLayoutManager1);

        ItemTouchHelper.SimpleCallback simpleItemTouchCallback = new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT) {
            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                Log.d(TAG, "onMove: ");
                return false;
            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
                Log.d(TAG, "onSwiped: ");
            }
        };

        ItemTouchHelper touchHelper = new ItemTouchHelper(simpleItemTouchCallback);
        touchHelper.attachToRecyclerView(recyclerView);

Answer 1

I forgot two things:

**1. update the SimpleCallback to this:

ItemTouchHelper.SimpleCallback simpleItemTouchCallback = new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT) {
            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                // Notify Adapter of the moved item!
                recyclerView.getAdapter().notifyItemMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
                return true;
            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
                // No swipe action
            }

            @Override
            public boolean isItemViewSwipeEnabled() {
                // Disable swipe (dont override this method or return true, if you want to have swipe)
                return false;
            }

            @Override
            public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
                // Set movement flags to specify the movement direction
                // final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.RIGHT | ItemTouchHelper.LEFT;  <-- for all directions
                // In this case only up and down is allowed
                final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
                final int swipeFlags = 0;
                return makeMovementFlags(dragFlags, swipeFlags);
            }
        };

Especially important is to overwrite getMovementFlags() to specify the direction for dragging and notify the adapter of the moved Item, as I do in onMove()

2. Trigger dragging by itemTouchHelper.startDrag(viewHolderElement):

I did this by creating a small interface in the RecyclerViewAdapter:

public interface OnStartDragListener {
        void onStartDrag(RecyclerView.ViewHolder holder);
    }

When creating the Adapter pass in a new OnStartDragListenerElement like so:

EditIngredientsRecyclerViewAdapter premixableIngredientsAdapter = new EditIngredientsRecyclerViewAdapter(this, typeOfComponents, new EditIngredientsRecyclerViewAdapter.OnStartDragListener() {
            @Override
            public void onStartDrag(RecyclerView.ViewHolder holder) {
                touchHelper.startDrag(holder);
                Log.d(TAG, "onStartDrag: ");
            }
        });

and calling onStartDrag(viewHolder) in an Touchlistener put on a button in the view like so:

holder.itemBinding.dragBtn.setOnTouchListener(new View.OnTouchListener() {
                @Override
                public boolean onTouch(View v, MotionEvent event) {
                    mOnStartDragListener.onStartDrag(holder);
                    return false;
                }
            });

I am sure, there are more efficient implementations and once somebody posts one here, I will accept it. However, this at least made it working for me.

Answer 2

I've listed code for both ItemTouchHelper.SimpleCallback and ItemTouchHelper.Callback(). Comments are listed in the code to help break down whats happening.

ItemTouchHelper.SimpleCallback In the Activity/Fragment under the RecyclerView implementation Create a ItemTouchHelper.SimpleCallback object. You'll need to override onMove() and onSwiped() methods.

ItemTouchHelper(object : ItemTouchHelper.SimpleCallback(
    ItemTouchHelper.UP or ItemTouchHelper.DOWN,
    ItemTouchHelper.RIGHT or ItemTouchHelper.LEFT
) {


    // You'll need to Override
    override fun onMove(
        recyclerView: RecyclerView,
        viewHolder: ViewHolder,
        target: ViewHolder
    ): Boolean {
        // Get the position start position of the item
        val startPosition = viewHolder.adapterPosition
        // Get the endPosition, where you draged it to. 
        val endPosition = target.adapterPosition

        // Submit start and end position to notifyItemMoved. 
        recyclerView.adapter?.notifyItemMoved(startPosition, endPosition)

        // true if moved, false otherwise
        return true
    }

    override fun onSwiped ...

If you want to create a CustomItemTouchCallback

Create a customItemTouchHelper class that extends ItemTouchHelper.Callback(), you'll need to override getMovementFlags(), onMove(), and onSwiped()

class CustomItemTouchHelper(mContext: Context, val viewModel: MyViewModel) : ItemTouchHelper.Callback() {

    override fun getMovementFlags(
        recyclerView: RecyclerView,
        viewHolder: RecyclerView.ViewHolder
    ): Int {
        val  dragFlags = ItemTouchHelper.UP or ItemTouchHelper.DOWN
        val swipeFlags = ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT
        return makeMovementFlags(dragFlags, swipeFlags)
    }

    override fun onMove(
        recyclerView: RecyclerView,
        viewHolder: RecyclerView.ViewHolder,
        target: RecyclerView.ViewHolder
    ): Boolean {
        val startPosition = viewHolder.adapterPosition
        val endPosition = target.adapterPosition
        
        recyclerView.adapter?.notifyItemMoved(fromPosition, toPosition)
        // true if moved, false otherwise 
        return true
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        val editList: MutableList<User>? = viewModel.usersList?.value as MutableList<User>?
        val editListCopy = editList?.toMutableList()
        editListCopy?.removeAt(viewHolder.adapterPosition)
        viewModel.usersList?.postValue(editListCopy)
    }

    override fun isItemViewSwipeEnabled(): Boolean {
        // Allows items to be swiped left or right.
        return true
    }

    override fun isLongPressDragEnabled(): Boolean {
        // Allows for long click so items can be dragged, moved up or down in the list. 
        return true
    }
}

Now in your Activity or Fragment, you'll need to create a CustomItemHelper object and then attach the RecyclerView to it.

val rv = findViewById<RecyclerView>(R.id.recycler_view)
    rv.apply {
        ...
        val customItemTouchHelper = ItemTouchHelper(CustomItemTouchHelper(context, viewModel))
        customItemTouchHelper.attachToRecyclerView(rv)

        }

Answer 3

I'm sorry, I don't have enough reputation to comment under the question. Try changing return false to return true

Answer 4

Your ItemTouchHelper.SimpleCallback should set the move flags in the constructor and the onMove method should return true.

int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
int swipeFlags = ItemTouchHelper.LEFT;
ItemTouchHelper.SimpleCallback simpleItemTouchCallback = new ItemTouchHelper.SimpleCallback(moveFlags, swipeFlags) {
            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                Log.d(TAG, "onMove: ");
                int fromPosition = viewHolder.getAdapterPosition();
                int toPosition = target.getAdapterPosition();
                // Swap list items in adapter...
                return true;
            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
                Log.d(TAG, "onSwiped: ");
            }
        }