android - 如何捕捉与 RecyclerView 一起使用的 ItemTouchHelper 的 Drop 动作

Question

RecyclerView的ItemTouchHelper有问题。

我正在制作游戏。游戏板实际上是一个 RecyclerView。 RecyclerView 有 GridLayoutManager 和一些跨度计数。我想实现 拖放 recyclerview 的项目。任何项目都可以在所有方向（上、下、左、右）上拖动。

private void initializeLayout() {
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutFrozen(true);
    recyclerView.setNestedScrollingEnabled(false);

    // set layout manager
    GridLayoutManager layoutManager = new GridLayoutManager(getContext(), BOARD_SIZE,
        LinearLayoutManager.VERTICAL, true);
    recyclerView.setLayoutManager(layoutManager);

    // Extend the Callback class
    ItemTouchHelper.Callback itemTouchCallback = new ItemTouchHelper.Callback() {

    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        Log.w(TAG, "onMove");
        return false;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        // Application does not include swipe feature.
    }

    @Override
    public void onMoved(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
                        int fromPos, RecyclerView.ViewHolder target, int toPos, int x, int y) {
        Log.d(TAG, "onMoved");
        // this is calling every time, but I need only when user dropped item, not after every onMove function.
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return false;
    }

    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.START | ItemTouchHelper.END;
        int swipeFlags = 0;
        return makeMovementFlags(dragFlags, swipeFlags);
    }
    };

    ItemTouchHelper touchHelper = new ItemTouchHelper(itemTouchCallback);
    touchHelper.attachToRecyclerView(recyclerView);
}

那么，当我仍在 RecyclerView 上拖动项目时，为什么 ItemTouchHelper 的 onMoved 功能有效？我怎样才能做到这一点？

Answer 1

在拖放项目时，onMove() 可以被多次调用，而 clearView() 将被调用一次。所以你可以用它来表示拖动结束（发生了下降）。 并使用两个变量 dragFrom 和 dragTo 来跟踪完成的“拖放”中的实际位置。

private ItemTouchHelper.Callback dragCallback = new ItemTouchHelper.Callback() {

    int dragFrom = -1;
    int dragTo = -1;

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        return makeMovementFlags(ItemTouchHelper.UP|ItemTouchHelper.DOWN|ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT,
                0);
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {

        int fromPosition = viewHolder.getAdapterPosition();
        int toPosition = target.getAdapterPosition();


        if(dragFrom == -1) {
            dragFrom =  fromPosition;
        }
        dragTo = toPosition;

        adapter.onItemMove(fromPosition, toPosition);

        return true;
    }

    private void reallyMoved(int from, int to) {
        // I guessed this was what you want...
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {

    }

    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return false;
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);

        if(dragFrom != -1 && dragTo != -1 && dragFrom != dragTo) {
            reallyMoved(dragFrom, dragTo);
        }

        dragFrom = dragTo = -1;
    }

};

adapter.onItemMove(fromPosition, toPosition) 如下：

public void onItemMove(int fromPosition, int toPosition) {
    list.add(toPosition, list.remove(fromPosition));
    notifyItemMoved(fromPosition, toPosition);
}

Answer 2

onSelectedChanged(RecyclerView.ViewHolder, int) 回调提供有关当前 actionState 的信息：
- ACTION_STATE_IDLE:
- ACTION_STATE_DRAG
- ACTION_STATE_SWIPE

这样你就可以跟踪订单是否改变了，当状态变为ACTION_STATE_IDLE时，你可以做你需要做的！

例子：

private final class MyCallback extends ItemTouchHelper.Callback {
    private boolean mOrderChanged;

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        // Check if positions of viewHolders correspond to underlying model, and if not, flip the items in the model and set the mOrderChanged flag
        mOrderChanged = true;
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
    super.onSelectedChanged(viewHolder, actionState);

    if (actionState == ItemTouchHelper.ACTION_STATE_IDLE && mOrderChanged) {
        doSomething();
        mOrderChanged = false;
    }
}

Answer 3

我做了一些测试，onSelectedChanged(RecyclerView.ViewHolder?, Int) 对我来说似乎最可靠地检测到手势结束（下降）。每当拖动项目并传递ACTION_STATE_DRAG 的操作状态时，都会调用该方法。当拖动结束时，它以ACTION_STATE_IDLE 的动作状态被调用。

请参阅下面的解决方案。 onItemDrag(Int, Int) 回调用于在拖动项目时重新排序适配器中的项目。另一方面，onItemDragged(Int, Int) 回调用于在手势结束时更新数据库中的位置。

class ItemGestureHelper(private val listener: OnItemGestureListener) : ItemTouchHelper.Callback() {

    interface OnItemGestureListener {

        fun onItemDrag(fromPosition: Int, toPosition: Int): Boolean

        fun onItemDragged(fromPosition: Int, toPosition: Int)

        fun onItemSwiped(position: Int)
    }

    private var dragFromPosition = -1
    private var dragToPosition = -1

    // Other methods omitted...

    override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
        // Item is being dragged, keep the current target position
        dragToPosition = target.adapterPosition
        return listener.onItemDrag(viewHolder.adapterPosition, target.adapterPosition)
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        listener.onItemSwiped(viewHolder.adapterPosition)
    }

    override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
        super.onSelectedChanged(viewHolder, actionState)

        when (actionState) {
            ItemTouchHelper.ACTION_STATE_DRAG -> {
                viewHolder?.also { dragFromPosition = it.adapterPosition }
            }
            ItemTouchHelper.ACTION_STATE_IDLE -> {
                if (dragFromPosition != -1 && dragToPosition != -1 && dragFromPosition != dragToPosition) {
                    // Item successfully dragged
                    listener.onItemDragged(dragFromPosition, dragToPosition)
                    // Reset drag positions
                    dragFromPosition = -1
                    dragToPosition = -1
                }
            }
        }
    }

}

Answer 4

您必须在适配器中实现 OnMove 侦听器：

Collections.swap(youCoolList, fromPosition, toPosition); notifyItemMoved(fromPosition, toPosition);

喜欢这个人 https://medium.com/@ipaulpro/drag-and-swipe-with-recyclerview-b9456d2b1aaf#.blviq6jxp

特殊网格示例 https://medium.com/@ipaulpro/drag-and-swipe-with-recyclerview-6a6f0c422efd#.xb74uu7ke