使用三根手指触发触摸取消

Question

我有一个简单的应用程序，可以打印所有触摸事件的坐标。 在模拟器中它很有效。

在我的设备（iPhone）上，它最适合，最多两个手指。当我用快速序列中的三根手指点击时，会触发事件touchesCancelled。

有人可以向我解释一下吗？ 这是我的UIView中的打印代码（如果问题出现在那里）。

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInView:touch.view];
        NSLog(@"Began  %f %f",  location.x, location.y);
    }
}


-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{  
    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInView:touch.view];
        NSLog(@"Moved  %f %f",  location.x, location.y);
    }
}


-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInView:touch.view];
        NSLog(@"Ended  %f %f",  location.x, location.y);
    }
}

-(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"Phase: Touches cancelled");

    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInView:touch.view];
        NSLog(@"Cancelled  %f %f",  location.x, location.y);

    }
}

序列的一个例子就是这个：

Began  38.000000 263.000000
Began  173.500000 238.500000
Moved  41.500000 263.000000
Phase: Touches cancelled   <<<< third touch
Cancelled  41.500000 263.000000
Cancelled  173.500000 238.500000

谢谢。