问题描述：UITableView添加手势后，经过一次滚动不能再次滚动
解决办法：将添加的手势delegate设置为self，并在self中实现协议<UIGestureRecognizerDelegate>如下：
-(BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{
return YES;
}
该方法官方说明：
Asks the delegate if two gesture recognizers should be allowed to recognize gestures simultaneously.
询问委托如果有两个手势，是否允许一起识别。
