android - 使用 GridLayoutManager 在 RecyclerView 中拖放项目

Question

我想要实现的目标:有一个带有 GridLayoutManager 的 RecyclerView，它支持拖放并在拖动时重新排列项目。

旁注:第一次使用拖放开发任何东西。

关于如何使用 ListView 实现此功能的主题很多，例如:https://raw.githubusercontent.com/btownrippleman/FurthestProgress/master/FurthestProgress/src/com/anappforthat/android/languagelineup/DynamicListView.java

但是，示例通常包含大量代码，用于创建拖动 View 的位图，感觉应该可以使用 View.startDrag(...) 和RecyclerView 带有 notifyItemAdded()、notifyItemMoved() 和 notifyItemRemoved()，因为它们提供重新排列动画。

所以我玩了一些并想出了这个:

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);

这段代码有点工作，我得到了交换，但非常不稳定/不稳定，有时当它刷新时，整个网格会重新排列回原始顺序或随机的东西。无论如何，上面的代码只是我的第一次快速尝试，我真正更感兴趣的是是否有一些标准/最佳实践方法可以使用 ReyclerView 进行拖放，或者解决它的正确方法是否仍然相同多年来一直用于 ListViews？

Answer 1

实际上有更好的方法来实现这一点。您可以使用一些 RecyclerView 的“companion”类:

ItemTouchHelper ，即

a utility class to add swipe to dismiss and drag & drop support to RecyclerView.

及其ItemTouchHelper.Callback ，即

the contract between ItemTouchHelper and your application

// 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);
    }
};

有关更多详细信息，请查看他们的文档。