用GridLayoutManager拖放RecycerView中的项

Question

附注：第一次用拖放开发任何东西。

关于如何使用ListView实现此功能，有很多主题，例如：https://raw.githubusercontent.com/btownRippleman/furthestProgress/master/furthestProgress/src/com/anappforthat/android/languagelineup/dynamicListView.java

但是，这些示例通常使用大量代码创建拖动视图的位图，并且使用view.startdrag（...）和RecyerView使用NotifyItemAddad()、NotifyItemMoved()和NotifyItemRemoved()应该可以获得相同的结果，因为它们提供了重新排列的动画。

所以我玩了一些，想出了这个：

final CardAdapter adapter = new CardAdapter(list);
adapter.setHasStableIds(true);
adapter.setListener(new CardAdapter.OnLongClickListener() {
    @Override
    public void onLongClick(View view) {
        ClipData data = ClipData.newPlainText("","");
        View.DragShadowBuilder builder = new View.DragShadowBuilder(view);
        final int pos = mRecyclerView.getChildAdapterPosition(view);
        final Goal item = list.remove(pos);

        mRecyclerView.setOnDragListener(new View.OnDragListener() {
            int prevPos = pos;

            @Override
            public boolean onDrag(View view, DragEvent dragEvent) {
                final int action = dragEvent.getAction();
                switch(action) {
                    case DragEvent.ACTION_DRAG_LOCATION:
                        View onTopOf = mRecyclerView.findChildViewUnder(dragEvent.getX(), dragEvent.getY());
                        int i = mRecyclerView.getChildAdapterPosition(onTopOf);

                        list.add(i, list.remove(prevPos));
                        adapter.notifyItemMoved(prevPos, i);
                        prevPos = i;
                        break;

                    case DragEvent.ACTION_DROP:
                        View underView = mRecyclerView.findChildViewUnder(dragEvent.getX(), dragEvent.getY());
                        int underPos = mRecyclerView.getChildAdapterPosition(underView);

                        list.add(underPos, item);
                        adapter.notifyItemInserted(underPos);
                        adapter.notifyDataSetChanged();
                        break;
                }

                return true;
            }
        });

        view.startDrag(data, builder, view, 0);
    }
});
mRecyclerView.setAdapter(adapter);

这段代码的工作，我得到了交换，但非常不稳定/不稳定，有时当它刷新时，整个网格被重新排列回到原来的顺序或一些随机的东西。无论如何，上面的代码只是我的第一次快速尝试，我真正感兴趣的是，是否有一些标准/最佳实践方法来使用ReyclerView进行拖放，或者解决它的正确方法是否仍然与ListViews多年来使用的方法相同？

Answer 1

实际上有一个更好的方法来实现这一点。您可以使用RecycerView的一些“配套”类：

ItemTouchHelper，它是

一个实用程序类，用于添加swipe以解除和RecycerView的拖放支持。

// Create an `ItemTouchHelper` and attach it to the `RecyclerView`
ItemTouchHelper ith = new ItemTouchHelper(_ithCallback);
ith.attachToRecyclerView(rv);

// Extend the Callback class
ItemTouchHelper.Callback _ithCallback = new ItemTouchHelper.Callback() {
    //and in your imlpementaion of
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        // get the viewHolder's and target's positions in your adapter data, swap them
        Collections.swap(/*RecyclerView.Adapter's data collection*/, viewHolder.getAdapterPosition(), target.getAdapterPosition());
        // and notify the adapter that its dataset has changed
        _adapter.notifyItemMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

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

    //defines the enabled move directions in each state (idle, swiping, dragging). 
    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        return makeFlag(ItemTouchHelper.ACTION_STATE_DRAG,
                ItemTouchHelper.DOWN | ItemTouchHelper.UP | ItemTouchHelper.START | ItemTouchHelper.END);
    }
};