TouchUpOutside无法正常工作

Question

我用一些自定义UIButton创建了一个menue。我只更改了drawRect函数：

for button in buttons {
            button.addTarget(self, action: #selector(showLabel), forControlEvents: .TouchDown)
            button.addTarget(self, action: #selector(buttonAction), forControlEvents: .TouchUpInside)
            button.addTarget(self, action: #selector(labelDelete), forControlEvents: .TouchUpOutside)
            button.addTarget(self, action: #selector(labelDelete), forControlEvents: .TouchCancel)
        }

我有三个功能来处理touchevents：

func labelDelete(sender: HexagonButton!) {
        label?.alpha = 0
        label?.hidden = true
    }
    func showLabel(sender: HexagonButton!) {
        label!.frame = CGRect(x: self.view.frame.width/2 - 150 + lastContentOffset, y: 5, width: 300, height: 30)
        label!.text = sender.labelName
        self.label?.hidden = false
        UIView.animateWithDuration(1.0, animations:{
            self.label?.alpha = 1
        })

    }
    func buttonAction(sender: HexagonButton!) {
        label?.alpha = 0
        label?.hidden = true
        if sender.viewControllerName != "nil" {
            let storyboard = UIStoryboard(name: "Main", bundle: nil)
            let vc = storyboard.instantiateViewControllerWithIdentifier(sender.viewControllerName)
            self.navigationController?.pushViewController(vc, animated: true)
        }

    }

如果我触摸一个按钮，标签就会显示出来。但是，如果我将手指从按钮移开并离开显示器，它仍然会调用.TouchUpInside函数。只有当我的手指离按钮很远时，它才能正常工作。这有什么问题？

请问！