Android RecyclerView的Item点击事件实现整理

自从开始使用RecyclerView代替ListView，会发现有很多地方需要学习。前一段时间的学习记录有：

RecyclerView的滚动事件研究 - DevWiki
RecyclerView的ViewHolder和Adapter的封装优化 - DevWiki
RecyclerView问题记录 - DevWiki

实现 RecyclerView的Item的点击事件有三种方式：

1. 在创建 ItemView时添加点击监听
2. 当 ItemView attach RecyclerView时实现
3. 通过RecyclerView已有的方法addOnItemTouchListener()实现

1.在创建ItemView时添加点击监听

思路是：因为ViewHolder我们可以拿到每个Item的根布局，所以如果我们为根布局设置单独的OnClick监听并将其开放给Adapter，那不就可以在组装RecyclerView时就能够设置ItemClickListener，只不过这个Listener不是设置到RecyclerView上而是设置到Adapter。具体实现代码如下：

public class SampleAdapter extends RecyclerView.Adapter<SampleAdapter.SampleViewHolder> { 

  private List<DataBean> mDatas;
  private OnItemClickListener mListener; // Item点击事件 

  public DataBean getItem(int position) {
    return mDatas == null ? null : mDatas.get(position);
  } 

  @Override
  public SampleViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent,false);
    return new SampleViewHolder(itemView);
  } 

  @Override
  public void onBindViewHolder(SampleViewHolder holder, int position) { 

  } 

  @Override
  public int getItemCount() {
    return mDatas == null ? 0 : mDatas.size();
  } 

  class SampleViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener, View.OnLongClickListener { 

    public SampleViewHolder(View itemView) {
      super(itemView);
      // TODO:初始化View
      ... 

      itemView.setOnClickListener(this);
      itemView.setOnLongClickListener(this);
    } 

    @Override
    public void onClick(View v) {
      if (mListener != null) {
        mListener.onItemClick(SampleAdapter.this, v, getLayoutPosition());
      }
    } 

    @Override
    public boolean onLongClick(View v) {
      if (mListener != null) {
        mListener.onItemLongClick(SampleAdapter.this, v, getLayoutPosition());
        return true;
      }
      return false;
    }
  }
}

2.当ItemView attach RecyclerView时实现

该实现方法是在阅读国外的一篇博客时发现的,原文链接如下：Getting your clicks on RecyclerView
实现的代码如下：

public class ItemClickSupport { 

  private static final int KEY = 0x99999999;
  private final RecyclerView mRecyclerView;
  private OnItemClickListener mOnItemClickListener;
  private OnItemLongClickListener mOnItemLongClickListener; 

  private View.OnClickListener mOnClickListener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      if (mOnItemClickListener != null) {
        RecyclerView.ViewHolder holder = mRecyclerView.getChildViewHolder(v);
        mOnItemClickListener.onItemClicked(mRecyclerView, v, holder.getAdapterPosition());
      }
    }
  }; 

  private View.OnLongClickListener mOnLongClickListener = new View.OnLongClickListener() {
    @Override
    public boolean onLongClick(View v) {
      if (mOnItemLongClickListener != null) {
        RecyclerView.ViewHolder holder = mRecyclerView.getChildViewHolder(v);
        return mOnItemLongClickListener.onItemLongClicked(mRecyclerView, v, holder.getAdapterPosition());
      }
      return false;
    }
  }; 

  private RecyclerView.OnChildAttachStateChangeListener mAttachListener = new RecyclerView.OnChildAttachStateChangeListener() { 

    @Override
    public void onChildViewAttachedToWindow(View view) {
      if (mOnItemClickListener != null) {
        view.setOnClickListener(mOnClickListener);
      }
      if (mOnItemLongClickListener != null) {
        view.setOnLongClickListener(mOnLongClickListener);
      }
    } 

    @Override
    public void onChildViewDetachedFromWindow(View view) {
    }
  }; 

  /**
   * ItemClickSupport的私有构造方法
   */
  private ItemClickSupport(RecyclerView recyclerView) {
    mRecyclerView = recyclerView;
    mRecyclerView.setTag(KEY, this);
    // 为RecyclerView设置OnChildAttachStateChangeListener事件监听
    mRecyclerView.addOnChildAttachStateChangeListener(mAttachListener);
  } 

  /**
   * 为RecyclerView设置ItemClickSupport
   */
  public static ItemClickSupport addTo(RecyclerView view) {
    ItemClickSupport support = (ItemClickSupport) view.getTag(KEY);
    if (support == null) {
      support = new ItemClickSupport(view);
    }
    return support;
  } 

  /**
   * 为RecyclerView移除ItemClickSupport
   */
  public static ItemClickSupport removeFrom(RecyclerView view) {
    ItemClickSupport support = (ItemClickSupport) view.getTag(KEY);
    if (support != null) {
      support.detach(view);
    }
    return support;
  } 

  /**
   * 为RecyclerView设置点击事件监听
   */
  public ItemClickSupport setOnItemClickListener(OnItemClickListener listener) {
    mOnItemClickListener = listener;
    return this;
  } 

  /**
   * 为RecyclerView设置长按事件监听
   */
  public ItemClickSupport setOnItemLongClickListener(OnItemLongClickListener listener) {
    mOnItemLongClickListener = listener;
    return this;
  } 

  /**
   * 为RecyclerView移除OnChildAttachStateChangeListener事件监听
   */
  private void detach(RecyclerView view) {
    view.removeOnChildAttachStateChangeListener(mAttachListener);
    view.setTag(KEY, null);
  } 

  /**
   * RecyclerView的点击事件监听接口
   */
  public interface OnItemClickListener {
    void onItemClicked(RecyclerView recyclerView, View itemView, int position);
  } 

  /**
   * RecyclerView的长按事件监听接口
   */
  public interface OnItemLongClickListener {
    boolean onItemLongClicked(RecyclerView recyclerView, View itemView, int position);
  }
}

上面的代码中给RecyclerView设置了OnChildAttachStateChangeListener事件监听，当子View attach RecyclerView时设置事件监听。

private RecyclerView.OnChildAttachStateChangeListener mAttachListener = new RecyclerView.OnChildAttachStateChangeListener() { 

 @Override
  public void onChildViewAttachedToWindow(View view) {
    if (mOnItemClickListener != null) {
      view.setOnClickListener(mOnClickListener);
    }
    if (mOnItemLongClickListener != null) {
      view.setOnLongClickListener(mOnLongClickListener);
    }
  } 

  @Override
  public void onChildViewDetachedFromWindow(View view) {}
};

使用时只需要调用addTo(RecycleView view)方法得到ItemClickSupport对象，然后调用setOnItemClickListener()方法和setOnItemLongClickListener()方法设置ItemView的点击事件和长按事件监听即可。

3.通过RecyclerView已有的方法addOnItemTouchListener()实现

3.1、查看源码

查看RecyclerView源码可以看到,RecyclerView预留了一个Item的触摸事件方法：

/**
 * Add an {@link OnItemTouchListener} to intercept touch events before they are dispatched
 * to child views or this view's standard scrolling behavior.
 *
 * <p>Client code may use listeners to implement item manipulation behavior. Once a listener
 * returns true from
 * {@link OnItemTouchListener#onInterceptTouchEvent(RecyclerView, MotionEvent)} its
 * {@link OnItemTouchListener#onTouchEvent(RecyclerView, MotionEvent)} method will be called
 * for each incoming MotionEvent until the end of the gesture.</p>
 *
 * @param listener Listener to add
 * @see SimpleOnItemTouchListener
 */
public void addOnItemTouchListener(OnItemTouchListener listener) {
  mOnItemTouchListeners.add(listener);
}

通过注释我们可知,此方法是在滚动事件之前调用，需要传入一个OnItemTouchListener对象。OnItemTouchListener的代码如下：

public static interface OnItemTouchListener {  

  public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e); 

  public void onTouchEvent(RecyclerView rv, MotionEvent e); 

  public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept);
}

此接口还提供了一个实现类，且官方推荐使用该实现类SimpleOnItemTouchListener：

/**
 * An implementation of {@link RecyclerView.OnItemTouchListener} that has empty method bodies and
 * default return values.
 *
 * You may prefer to extend this class if you don't need to override all methods. Another
 * benefit of using this class is future compatibility. As the interface may change, we'll
 * always provide a default implementation on this class so that your code won't break when
 * you update to a new version of the support library.
 */
public static class SimpleOnItemTouchListener implements RecyclerView.OnItemTouchListener {
  <span style="font-family:'Microsoft YaHei';">
</span>  @Override
  public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
    return false;
  } 

  @Override
  public void onTouchEvent(RecyclerView rv, MotionEvent e) {
  } 

  @Override
  public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
  }
}

在触摸接口中，当触摸时会回调一个MotionEvent对象，通过使用GestureDetectorCompat来解析用户的操作。

3.2、了解GestureDetector的工作原理

对于触摸屏，其原生的消息无非按下、抬起、移动这几种，我们只需要简单重载onTouch或者设置触摸侦听器setOnTouchListener即可进行处理。不过，为了提高我们的APP的用户体验，有时候我们需要识别用户的手势，Android给我们提供的手势识别工具GestureDetector就可以帮上大忙了。

GestureDetector的工作原理是，当我们接收到用户触摸消息时，将这个消息交给GestureDetector去加工，我们通过设置侦听器获得GestureDetector处理后的手势。

GestureDetector提供了两个侦听器接口，OnGestureListener处理单击类消息，OnDoubleTapListener处理双击类消息。
OnGestureListener的接口有这几个：

// 单击，触摸屏按下时立刻触发
abstract boolean onDown(MotionEvent e);
// 抬起，手指离开触摸屏时触发(长按、滚动、滑动时，不会触发这个手势)
abstract boolean onSingleTapUp(MotionEvent e);
// 短按，触摸屏按下后片刻后抬起，会触发这个手势，如果迅速抬起则不会
abstract void onShowPress(MotionEvent e);
// 长按，触摸屏按下后既不抬起也不移动，过一段时间后触发
abstract void onLongPress(MotionEvent e);
// 滚动，触摸屏按下后移动
abstract boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);
// 滑动，触摸屏按下后快速移动并抬起，会先触发滚动手势，跟着触发一个滑动手势
abstract boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY);
OnDoubleTapListener的接口有这几个：

// 双击，手指在触摸屏上迅速点击第二下时触发
abstract boolean onDoubleTap(MotionEvent e);
// 双击的按下跟抬起各触发一次
abstract boolean onDoubleTapEvent(MotionEvent e);
// 单击确认，即很快的按下并抬起，但并不连续点击第二下
abstract boolean onSingleTapConfirmed(MotionEvent e);

有时候我们并不需要处理上面所有手势，方便起见，Android提供了另外一个类SimpleOnGestureListener实现了如上接口，我们只需要继承SimpleOnGestureListener然后重载需要的手势即可。

3.3、实现点击事件监听

了解了GestureDetector的工作原理之后，便开始实现RecycleView的Item的点击事件。首先写一个SimpleRecycleViewItemClickListener类继承SimpleOnItemTouchListener，构造时传入Item点击回调OnItemClickListener，并覆写父类的boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e)方法，具体代码如下：

/**
 * RecyclerView的Item点击事件监听
 *
 * @author liyunlong
 * @date 2016/11/21 9:42
 */
public class SimpleRecycleViewItemClickListener extends RecyclerView.SimpleOnItemTouchListener { 

  private OnItemClickListener mListener;
  private GestureDetectorCompat mGestureDetector; 

  public SimpleRecycleViewItemClickListener(OnItemClickListener listener) {
    this.mListener = listener;
  } 

  @Override
  public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
    if (mGestureDetector == null) {
      initGestureDetector(rv);
    }
    if (mGestureDetector.onTouchEvent(e)) { // 把事件交给GestureDetector处理
      return true;
    } else {
      return false;
    }
  } 

  /**
   * 初始化GestureDetector
   */
  private void initGestureDetector(final RecyclerView recyclerView) {
    mGestureDetector = new GestureDetectorCompat(recyclerView.getContext(), new GestureDetector.SimpleOnGestureListener() { // 这里选择SimpleOnGestureListener实现类，可以根据需要选择重写的方法 

      /**
       * 单击事件
       */
      @Override
      public boolean onSingleTapUp(MotionEvent e) {
        View childView = recyclerView.findChildViewUnder(e.getX(), e.getY());
        if (childView != null && mListener != null) {
          mListener.onItemClick(childView, recyclerView.getChildLayoutPosition(childView));
          return true;
        }
        return false;
      } 

      /**
       * 长按事件
       */
      @Override
      public void onLongPress(MotionEvent e) {
        View childView = recyclerView.findChildViewUnder(e.getX(), e.getY());
        if (childView != null && mListener != null) {
          mListener.onItemLongClick(childView, recyclerView.getChildLayoutPosition(childView));
        }
      } 

      /**
       * 双击事件
       */
      @Override
      public boolean onDoubleTapEvent(MotionEvent e) {
        int action = e.getAction();
        if (action == MotionEvent.ACTION_UP) {
          View childView = recyclerView.findChildViewUnder(e.getX(), e.getY());
          if (childView != null && mListener != null) {
            mListener.onItemDoubleClick(childView, recyclerView.getChildLayoutPosition(childView));
            return true;
          }
        }
        return false;
      } 

    }); 

  } 

  /**
   * RecyclerView的Item点击事件监听接口
   *
   * @author liyunlong
   * @date 2016/11/21 9:43
   */
  public interface OnItemClickListener { 

    /**
     * 当ItemView的单击事件触发时调用
     */
    void onItemClick(View view, int position); 

    /**
     * 当ItemView的长按事件触发时调用
     */
    void onItemLongClick(View view, int position); 

    /**
     * 当ItemView的双击事件触发时调用
     */
    void onItemDoubleClick(View view, int position);
  } 

  /**
   * RecyclerView的Item点击事件监听实现
   *
   * @author liyunlong
   * @date 2016/11/21 10:05
   */
  public class SimpleOnItemClickListener implements OnItemClickListener { 

    @Override
    public void onItemClick(View view, int position) { 

    } 

    @Override
    public void onItemLongClick(View view, int position) { 

    } 

    @Override
    public void onItemDoubleClick(View view, int position) { 

    }
  }
}

在GestureDetectorCompat的手势回调中我们覆写：

1. boolean onSingleTapUp(MotionEvent e)：单击事件回调
2. void onLongPress(MotionEvent e)：长按事件回调
3. boolean onDoubleTapEvent(MotionEvent e)：双击事件回调

如果我们只需要监听单击事件，而不需要监听长按事件和双击事件，构造SimpleRecycleViewItemClickListener时只需要传入SimpleOnItemClickListener即可，如果需要处理其它的手势监听，也可以覆写对应的手势回调方法。

4.三种方法对比

以上三种方式分别是：

1. 在创建ItemView时添加点击监听
2. 当ItemView attach RecyclerView时实现
3. 通过RecyclerView已有的方法addOnItemTouchListener()实现

从以上三种方式的实现过程可知:

三种均可实现ItemView的点击事件和长按事件的监听。

第一种和第二种方式可以很方便对ItemView中的子View进行监听。

第三种方式可以很方便获取用户点击的坐标。

第二种方式和第三种方式可以写在单独的类中，相对于第一种写在Adapter的方式可使代码更独立整洁。

综上所述:

如果你只想监听ItemView的点击事件或长按事件，三种方式均可。

如果你想监听ItemView中每个子View的点击事件，采用第一种或者第二种比较方便。

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