设置是否支持多点触摸.默认为单点触摸
        self.multipleTouchEnabled = YES;
    


碰撞检测:过程

UIApplication --> UIWindow --> UIviewController -->视图控制器View --> 父视图 --> 子视图

事件响应

子视图 --> 父视图 --> 视图控制器 --> UIviewController --> UIWindow --> UIApplication



- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSArray * arr = [touches allObjects];


    UITouch * touch = arr[0];
   CGPoint Point_1 = [touch locationInView:self];
 

    if ([arr count] == 2) {
          UITouch * touch1 = arr[1];
        CGPoint Point_2 = [touch1 locationInView:self];
     

    }
    

获取手指对象

  UITouch * touch = [touches anyObject];


获取移动之后手指在视图上的位置

 CGPoint point = [touch locationInView:self.superview];

 self.center = CGPointMake(point.x, point.y);

  

    CGPoint currenPoint = [touch locationInView:self];


获取移动之前和移动之后的变化量

    CGFloat dx = currenPoint.x - _pervPoint.x;

   CGFloat dy = currenPoint.y - _pervPoint.y;

 

  self.center = CGPointMake(self.center.x + dx, self.center.y+dy);
    
}