从ListView开始，就有许多开源的滑动删除和拖拽的开源库。不过大多是基于View.OnDragListener实现的。还有的自己写touch事件监听，即繁琐又不优雅。RecyclerView的出现，让人耳目一新。拖拽和侧滑的实现当然也不能再low了。
正如用GestureDetectorCompat为RecycleView添加点击事件一样，拖拽和侧滑Google也有针对RecycleView的api。用起来so easy。

onInterceptTouchEvent

onInterceptTouchEvent类，包含在Android Support Library之中。它的功能正如注释所说：

  /**
 * This is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.
 * <p>
 * It works with a RecyclerView and a Callback class, which configures what type of interactions
 * are enabled and also receives events when user performs these actions.
 * <p>
 * Depending on which functionality you support, you should override
 * {@link Callback#onMove(RecyclerView, ViewHolder, ViewHolder)} and / or
 * {@link Callback#onSwiped(ViewHolder, int)}.
 * <p>
 * This class is designed to work with any LayoutManager but for certain situations, it can be
 * optimized for your custom LayoutManager by extending methods in the
 * {@link ItemTouchHelper.Callback} class or implementing {@link ItemTouchHelper.ViewDropHandler}
 * interface in your LayoutManager.
 * <p>
 * By default, ItemTouchHelper moves the items' translateX/Y properties to reposition them. On
 * platforms older than Honeycomb, ItemTouchHelper uses canvas translations and View's visibility
 * property to move items in response to touch events. You can customize these behaviors by
 * overriding {@link Callback#onChildDraw(Canvas, RecyclerView, ViewHolder, float, float, int,
 * boolean)}
 * or {@link Callback#onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int,
 * boolean)}.
 * <p/>
 * Most of the time, you only need to override <code>onChildDraw</code> but due to limitations of
 * platform prior to Honeycomb, you may need to implement <code>onChildDrawOver</code> as well.
 */

Google为我们实现了两千多行的代码。我们需要关心的只有ItemTouchHelper.Callback接口的三个方法而已。

/**设置我们拖动的方向以及侧滑的方向的*/
@Override
 public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
 return 0;
 }
 /**拖动item时会回调此方法*/
 @Override
 public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {

 return false;
 }
 /**侧滑item时会回调此方法*/
 @Override
 public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {

 }

开搞：
第一步，新建SimpleItemTouchHelperCallback类继承ItemTouchHelper.Callback。重写上述三个方法。由于RecycleView的布局有多种，所以我们首先要判断拖拽方向，如果是ListView形式的，就是上下拖拽，如果的GridvView形式的，就上下左右均可拖拽,所以对getMovementFlags重写：

   //如果是ListView样式的RecyclerView
        if (recyclerView.getLayoutManager() instanceof LinearLayoutManager){
            //设置拖拽方向为上下
            final int dragFlags = ItemTouchHelper.UP|ItemTouchHelper.DOWN;
            //设置侧滑方向为从左到右和从右到左都可以
            final int swipeFlags = ItemTouchHelper.START|ItemTouchHelper.END;
            //将方向参数设置进去
            return makeMovementFlags(dragFlags,swipeFlags);
        }else{//如果是GridView样式的RecyclerView
            //设置拖拽方向为上下左右
            final int dragFlags = ItemTouchHelper.UP|ItemTouchHelper.DOWN|
                    ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT;
            //不支持侧滑
            final int swipeFlags = 0;
            return makeMovementFlags(dragFlags,swipeFlags);
        }

拖拽后位置的变动需要我们的Adapter数据改变才，所以声明一个接口，

    public interface onMoveAndSwipedListener {
    boolean onItemMove(int fromPosition , int toPosition);
    void onItemDismiss(int position);
    }

通过构造方法传进来Adapter的监听：

    private onMoveAndSwipedListener mAdapter;
public SimpleItemTouchHelperCallback(onMoveAndSwipedListener listener)
{
    mAdapter =  listener;
}

实现拖拽，在onMove里调用：

        //回调adapter中的onItemMove方法
    mAdapter.onItemMove(viewHolder.getAdapterPosition(),target.getAdapterPosition());

实现侧滑删除，在onSwiped里调用：

 //回调adapter中的onItemDismiss方法
    mAdapter.onItemDismiss(viewHolder.getAdapterPosition());

ItemTouchHelper就编写好了。。。简单吧。下面Adapter去实现着这个回掉接口：

//还是我们的第一个适配器。。。
implements SimpleItemTouchHelperCallback.onMoveAndSwipedListener{


@Override
public boolean onItemMove(int fromPosition, int toPosition)
{
    //交换mItems数据的位置
    Collections.swap(mData,fromPosition,toPosition);
    //交换RecyclerView列表中item的位置
    notifyItemMoved(fromPosition,toPosition);
    return true;
}

@Override
public void onItemDismiss(int position)
{
    //删除mItems数据
    mData.remove(position);
    //删除RecyclerView列表对应item
    notifyItemRemoved(position);
}

ok。运行试试吧：

1.gif

想试试多布局？用上篇的MoreItemAdapter实现接口：

public class MoreItemAdapter extends MultiItemTypeAdapter<String> implements SimpleItemTouchHelperCallback.onMoveAndSwipedListener

1.gif

一样好使。
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