android recycleview实现拖动排序

实现以下的效果长按拖动，从而达到排序：

image.png
image.png

自定义以下接口：

interface ItemTouchHelperAdapter {

    //数据交换
    fun onItemMove(fromPosition: Int, toPosition: Int)

    //数据删除
    fun onItemDissmiss(position: Int)

}

自定义一个类实现实现ItemTouchHelper.Callback接口：

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback{

    private ItemTouchHelperAdapter mAdapter;

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

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

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

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

    @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) {
        mAdapter.onItemDissmiss(viewHolder.getAdapterPosition());
    }
}

adapter实现ItemTouchHelperAdapter 接口：

class StoreClassAdapter(var context: Context,var listData:ArrayList<String>)
    : RecyclerView.Adapter<StoreClassAdapter.ViewHolder>(), ItemTouchHelperAdapter {

    override fun onItemMove(fromPosition: Int, toPosition: Int) {
        //交换位置
        Collections.swap(listData,fromPosition,toPosition);
        notifyItemMoved(fromPosition,toPosition)
    }

    override fun onItemDissmiss(position: Int) {
        //移除数据
        listData.removeAt(position)
        notifyItemRemoved(position)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {

        return StoreClassAdapter.ViewHolder(
            LayoutInflater.from(parent.context).inflate(
                R.layout.adapter_store_class_item_view,parent, false
            )
        )
    }

    override fun getItemCount(): Int {
        return listData.size
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {

        with(holder) {

            val itemBean = listData.get(position)

            tvName?.text = itemBean
            tvCount?.text = "商家数量：" + itemBean

        }
    }

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        var tvName: TextView? = null
        var tvCount: TextView? = null

        init {
            tvName = itemView.findViewById(R.id.tvName)
            tvCount = itemView.findViewById(R.id.tvCount)
        }
    }

}

activity中的案例代码如下：

 val linearLayoutManager = LinearLayoutManager(this)
        val dividerItemDecoration =
            DividerItemDecoration(this, DividerItemDecoration.VERTICAL)
        storeClassAdapter = StoreClassAdapter(this,listCard)
        //先实例化Callback
        val callback: ItemTouchHelper.Callback = SimpleItemTouchHelperCallback(storeClassAdapter)
        //用Callback构造ItemtouchHelper
        val touchHelper = ItemTouchHelper(callback)
        //调用ItemTouchHelper的attachToRecyclerView方法建立联系
        touchHelper.attachToRecyclerView(rvList)
        with(rvList) {
            layoutManager = linearLayoutManager
            addItemDecoration(dividerItemDecoration)
            adapter = storeClassAdapter
        }

这个是整个效果的重要方法

通过Collections的swap方法来实现list集合中的item位置互换