android 拖拽交换位置

Android 拖拽交换位置可以通过自定义 RecyclerView.ItemTouchHelper.Callback 来实现。具体步骤如下：

1. 自定义 RecyclerView.ItemTouchHelper.Callback 类，并重写以下方法：

- onMove()：返回 true 表示可以移动 item，保存被移动的 item 和目标位置的 item，然后交换它们的位置。
- onSwiped()：返回 true 表示可以滑动 item，不做任何操作即可。
- getMovementFlags()：返回可以支持的移动和滑动方向。

2. 在 RecyclerView 中调用 ItemTouchHelper.attachToRecyclerView() 方法，将自定义的 ItemTouchHelper.Callback 作为参数传入。

3. 在 RecyclerView.Adapter 中实现自定义的 ItemTouchHelper.Adapter 接口，并重写以下方法：

- onItemMove()：交换被移动的 item 和目标位置的 item。
- onItemDismiss()：不做任何操作即可。

示例代码如下：

public class ItemTouchHelperCallback extends ItemTouchHelper.Callback {
    private final ItemTouchHelperAdapter mAdapter;

    public ItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
        mAdapter = adapter;
    }

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

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

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

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
                          RecyclerView.ViewHolder target) {
        mAdapter.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        // do nothing
    }

    public interface ItemTouchHelperAdapter {
        boolean onItemMove(int fromPosition, int toPosition);

        void onItemDismiss(int position);
    }
}

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder>
        implements ItemTouchHelperCallback.ItemTouchHelperAdapter {
    private List<String> mData;

    public MyAdapter(List<String> data) {
        mData = data;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_view, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        holder.mTextView.setText(mData.get(position));
    }

    @Override
    public int getItemCount() {
        return mData.size();
    }

    @Override
    public boolean onItemMove(int fromPosition, int toPosition) {
        Collections.swap(mData, fromPosition, toPosition);
        notifyItemMoved(fromPosition, toPosition);
        return true;
    }

    @Override
    public void onItemDismiss(int position) {
        // do nothing
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;

        public ViewHolder(View view) {
            super(view);
            mTextView = view.findViewById(R.id.text_view);
        }
    }
}

public class MainActivity extends AppCompatActivity {
    private RecyclerView mRecyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mRecyclerView = findViewById(R.id.recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        List<String> data = new ArrayList<>();
        for (int i = 1; i <= 100; i++) {
            data.add("Item " + i);
        }
        MyAdapter adapter = new MyAdapter(data);
        ItemTouchHelperCallback callback = new ItemTouchHelperCallback(adapter);
        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(callback);
        itemTouchHelper.attachToRecyclerView(mRecyclerView);
        mRecyclerView.setAdapter(adapter);
    }
}