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

Question

RecyclerView 的 ItemTouchHelper 有问题。

我在做游戏。游戏板实际上是一个 RecyclerView。 RecyclerView 有 GridLayoutManager 和一些跨度数。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 函数有效？我怎样才能做到这一点？

Answer 1

拖放项目时，可以多次调用onMove()，但会调用一次clearView()。所以你可以用它来表示拖动已经结束(发生了下降)。并使用两个变量 dragFrom 和 dragTo 来跟踪完成的“拖放”中的真实位置。

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) 如下所示:

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