ItemTouchHelper.SimpleCallback onMove() 未触发

Question

我想在我的

RecyclerView

中实现拖放。据我发现，实现此目的的最佳方法是将

ItemTouchHelper

附加到

RecyclerView

。

onSwiped()

工作正常，但

onMove()

永远不会被触发。

这就是我所做的：

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

我忘记了两件事：

**1。将

SimpleCallback

更新为：

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);
            }
        };

特别重要的是覆盖

getMovementFlags()

以指定拖动方向并通知适配器移动的 Item，就像我在

onMove()

中所做的那样

2。通过

itemTouchHelper.startDrag(viewHolderElement)

触发拖动：

我通过在 RecyclerViewAdapter 中创建一个小界面来做到这一点：

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

创建适配器时，传入新的 OnStartDragListenerElement，如下所示：

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

并在 Touchlistener 中调用

onStartDrag(viewHolder)

，在视图中放置一个按钮，如下所示：

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

我确信，有更有效的实现，一旦有人在这里发布一个，我会接受它。然而，这至少让它对我有用。

Answer 2

我列出了 ItemTouchHelper.SimpleCallback 和 ItemTouchHelper.Callback() 的代码。代码中列出了注释，以帮助分解发生的情况。

ItemTouchHelper.SimpleCallback 在Activity/Fragment下的RecyclerView实现中创建一个ItemTouchHelper.SimpleCallback对象。您需要重写 onMove() 和 onSwiped() 方法。

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 ...

如果你想创建一个CustomItemTouchCallback

创建一个扩展 ItemTouchHelper.Callback() 的 customItemTouchHelper 类，您需要重写 getMovementFlags()、onMove() 和 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
    }
}

现在在您的 Activity 或 Fragment 中，您需要创建一个 CustomItemHelper 对象，然后将 RecyclerView 附加到它。

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

        }

Answer 3

抱歉，我没有足够的声誉来在该问题下发表评论。尝试将

return false

更改为

return true

Answer 4

您的

ItemTouchHelper.SimpleCallback

应在构造函数中设置移动标志，并且 onMove 方法应返回

true

。

int moveFlags = 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: ");
            }
        }