类描述：

通过系统提供的MotionEvent来监测各种手势和（触摸）事件。当一个指定的手势事件发生 时，GestureDetector.OnGestureListener回调函数将通告用户。这个类仅仅处理由触摸引发的MotionEvent（不能 处理由轨迹球引发的事件）。

类中的一些手势类型：

   1.boolean  onDoubleTap(MotionEvent e)解释：双击的第二下Touch down时触发 
   2.boolean  onDoubleTapEvent(MotionEvent e)解释：双击的第二下Touch down和up都会触发，可用e.getAction()区分。 
   3.boolean  onDown(MotionEvent e)解释：Touch down时触发 
   4.boolean  onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)解释：Touch了滑动一点距离后，up时触发。 
   5.void  onLongPress(MotionEvent e)解释：Touch了不移动一直Touch down时触发 
   6.boolean  onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY)解释：Touch了滑动时触发。 
   7.void  onShowPress(MotionEvent e)解释：Touch了还没有滑动时触发（与onDown，onLongPress）比较onDown只要Touch down一定立刻触发。而Touchdown后过一               会没有滑动先触发onShowPress再是onLongPress。所以Touchdown后一直不 滑动，onDown->onShowPress->onLongPress这个顺序触发。 
   8.boolean  onSingleTapConfirmed(MotionEvent e) 
   9.boolean  onSingleTapUp(MotionEvent e)解释：上面这两个函数都是在touch down后又没有滑动（onScroll），又没有长按（onLongPress），然后Touchup时触发。 
      点击一下非常快的（不滑动）Touchup：onDown->onSingleTapUp->onSingleTapConfirmed 
      点击一下稍微慢点的（不滑 动）Touchup：onDown->onShowPress->onSingleTapUp->onSingleTapConfirmed

使用方法：

构造出来，mGestureDetector = new GestureDetector(mGestureListener);

mGestureListener = new BookOnGestureListener();

class BookOnGestureListener implements OnGestureListener {
同时要public boolean onTouchEvent(MotionEvent event) {
    mGestureListener .onTouchEvent(event);
}

这样就可以判断手势MotionEvent 的类型了，然后做出一些处理。

下面贴出一个类做参考、

class BookOnGestureListener implements OnGestureListener {
  public boolean onDown(MotionEvent event) {
   Log.d(LOG_TAG, "onDown");
   if (mState == BookState.ANIMATING)
    return false;
   float x = event.getX(), y = event.getY();
   int w = layoutWidth, h = layoutHeight;
   if (x * x + y * y < clickCornerLen) {
    if (indexPage > 0) {
     mSelectCorner = Corner.LeftTop;
     aniStartPos = new Point(0, 0);
    }
   } else if ((x - w) * (x - w) + y * y < clickCornerLen) {
    if (indexPage < totalPageNum - 1) {
     mSelectCorner = Corner.RightTop;
     aniStartPos = new Point(layoutWidth, 0);
    }
   } else if (x * x + (y - h) * (y - h) < clickCornerLen) {
    if (indexPage > 0) {
     mSelectCorner = Corner.LeftBottom;
     aniStartPos = new Point(0, layoutHeight);
    }
   } else if ((x - w) * (x - w) + (y - h) * (y - h) < clickCornerLen) {
    if (indexPage < totalPageNum - 1) {
     mSelectCorner = Corner.RightBottom;
     aniStartPos = new Point(layoutWidth, layoutHeight);
    }
   }
   if (mSelectCorner != Corner.None) {
    aniStopPos = new Point((int) x, (int) y);
    aniTime = 800;
    mState = BookState.ABOUT_TO_ANIMATE;
    closeBook = false;
    aniStartTime = new Date();
    mBookView.startAnimation();
   }
   return false;
  }

  public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
    float velocityY) {
   Log.d(LOG_TAG, "onFling velocityX:" + velocityX + " velocityY:"
     + velocityY);
   if (mSelectCorner != Corner.None) {
    if (mSelectCorner == Corner.LeftTop) {
     if (velocityX < 0) {
      aniStopPos = new Point(0, 0);
     } else {
      aniStopPos = new Point(2 * layoutWidth, 0);
     }
    } else if (mSelectCorner == Corner.RightTop) {
     if (velocityX < 0) {
      aniStopPos = new Point(-layoutWidth, 0);
     } else {
      aniStopPos = new Point(layoutWidth, 0);
     }
    } else if (mSelectCorner == Corner.LeftBottom) {
     if (velocityX < 0) {
      aniStopPos = new Point(0, layoutHeight);
     } else {
      aniStopPos = new Point(2 * layoutWidth, layoutHeight);
     }
    } else if (mSelectCorner == Corner.RightBottom) {
     if (velocityX < 0) {
      aniStopPos = new Point(-layoutWidth, layoutHeight);
     } else {
      aniStopPos = new Point(layoutWidth, layoutHeight);
     }
    }
    Log.d(LOG_TAG, "onFling animate");
    aniStartPos = new Point((int) scrollX, (int) scrollY);
    aniTime = 1000;
    mState = BookState.ABOUT_TO_ANIMATE;
    closeBook = true;
    aniStartTime = new Date();
    mBookView.startAnimation();
   }
   return false;
  }

  public void onLongPress(MotionEvent e) {
   Log.d(LOG_TAG, "onLongPress");
  }

  public boolean onScroll(MotionEvent e1, MotionEvent e2,
    float distanceX, float distanceY) {
   mState = BookState.TRACKING;
   if (mSelectCorner != Corner.None) {
    scrollX = e2.getX();
    scrollY = e2.getY();
    mBookView.startAnimation();
   }
   return false;
  }

  public void onShowPress(MotionEvent e) {
   Log.d(LOG_TAG, "onShowPress");
  }

  public boolean onSingleTapUp(MotionEvent e) {
   Log.d(LOG_TAG, "onSingleTapUp");

   if (mSelectCorner != Corner.None) {
    if (mSelectCorner == Corner.LeftTop) {
     if (scrollX < layoutWidth / 2) {
      aniStopPos = new Point(0, 0);
     } else {
      aniStopPos = new Point(2 * layoutWidth, 0);
     }
    } else if (mSelectCorner == Corner.RightTop) {
     if (scrollX < layoutWidth / 2) {
      aniStopPos = new Point(-layoutWidth, 0);
     } else {
      aniStopPos = new Point(layoutWidth, 0);
     }
    } else if (mSelectCorner == Corner.LeftBottom) {
     if (scrollX < layoutWidth / 2) {
      aniStopPos = new Point(0, layoutHeight);
     } else {
      aniStopPos = new Point(2 * layoutWidth, layoutHeight);
     }
    } else if (mSelectCorner == Corner.RightBottom) {
     if (scrollX < layoutWidth / 2) {
      aniStopPos = new Point(-layoutWidth, layoutHeight);
     } else {
      aniStopPos = new Point(layoutWidth, layoutHeight);
     }
    }
    aniStartPos = new Point((int) scrollX, (int) scrollY);
    aniTime = 800;
    mState = BookState.ABOUT_TO_ANIMATE;
    closeBook = true;
    aniStartTime = new Date();
    mBookView.startAnimation();
   }
   return false;
  }
}