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         ItemTouchHelper是谷歌提供的用于实现Recyclerview 拖拽效果的帮助类，今天我们来学习下它的基本用法

首先ItemTouchHelper需要实现它的一个内部抽象类CallBack

public class ItemTouchHelperCallback extends ItemTouchHelper.Callback {    private IMoveAndSwipeCallback iMoveAndSwipeCallback;    public void setiMoveAndSwipeCallback(IMoveAndSwipeCallback iMoveAndSwipeCallback) {        this.iMoveAndSwipeCallback = iMoveAndSwipeCallback;    }    /**     * 设置拖拽和item滑动的可支持方向     *     * @param recyclerView     * @param viewHolder     * @return     */    @Override    public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {        //支持上下拖拽        final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;        //item支持左滑        final int swipeFlags = ItemTouchHelper.LEFT;        return makeMovementFlags(dragFlags, swipeFlags);    }    /**     * 拖拽结束后（手指抬起）会回调的方法     *      * @param recyclerView     * @param viewHolder 手指拖拽的item     * @param viewHolder1 移动到的item     * @return     */    @Override    public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder viewHolder1) {        if (iMoveAndSwipeCallback != null) {            iMoveAndSwipeCallback.onMove(viewHolder.getAdapterPosition(), viewHolder1.getAdapterPosition());        }        return true;    }    /**     * 侧滑回调     *      * @param viewHolder     * @param swipeDir 方向     */    @Override    public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int swipeDir) {        if (iMoveAndSwipeCallback != null) {            iMoveAndSwipeCallback.onSwiped(viewHolder.getAdapterPosition());        }    }}

主要用到三个方法，getMovementFlags方法用于确定支持的拖拽方向和侧滑方向，onMove方法是拖拽结束后（手指抬起）会回调的方法，onSwiped则是侧滑回调，我这边还用了一个接口来给外部调用监听onMove和onSwiped

/** * 拖拽和侧滑抽象接口 */public interface IMoveAndSwipeCallback {    void onMove(int prePosition, int postPosition);    void onSwiped(int position);}

接下是我们在Activity中给RecyclerView设置ItemTouchHelper

public class ItemTouchHelperActivity extends AppCompatActivity implements IMoveAndSwipeCallback {    RecyclerView rv;    private List
   
     strings;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_item_touch_helper);        rv = findViewById(R.id.rv);        rv.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));        rv.addItemDecoration(new MyDecoration(this, MyDecoration.HORIZONTAL_LIST));        initData();        MyAdapter myAdapter = new MyAdapter(this);        rv.setAdapter(myAdapter);        //给RecyclerView设置ItemTouchHelper        ItemTouchHelperCallback itemTouchHelperCallback = new ItemTouchHelperCallback();        itemTouchHelperCallback.setiMoveAndSwipeCallback(this);        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(itemTouchHelperCallback);        itemTouchHelper.attachToRecyclerView(rv);    }    private void initData() {        strings = new ArrayList<>();        for (int i = 0; i < 20; i++) {            strings.add(String.valueOf(i));        }    }    @Override    public void onMove(int prePosition, int postPosition) {        Collections.swap(strings, prePosition, postPosition);        if (rv.getAdapter() != null) {            rv.getAdapter().notifyItemMoved(prePosition, postPosition);        }    }    @Override    public void onSwiped(int position) {        strings.remove(position);        if (rv.getAdapter() != null) {            rv.getAdapter().notifyItemRemoved(position);        }    }    class MyAdapter extends RecyclerView.Adapter {        private Context context;        public MyAdapter(Context context) {            this.context = context;        }        @NonNull        @Override        public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {            return new MyViewHolder(LayoutInflater.from(context).inflate(R.layout.item_text, viewGroup, false));        }        @Override        public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int i) {            MyViewHolder myViewHolder = (MyViewHolder) viewHolder;            myViewHolder.tv.setText(strings.get(i));        }        @Override        public int getItemCount() {            return strings.size();        }        class MyViewHolder extends RecyclerView.ViewHolder {            public TextView tv;            public MyViewHolder(@NonNull View itemView) {                super(itemView);                tv = itemView.findViewById(R.id.tv);            }        }    }}
   

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