swift - 按下时终止的自定义按钮

Question

我正在尝试创建一个自定义的UIButton。此自定义按钮显示未选中的框，当用户按下按钮时，该框将变为复选框。当用户按下复选框时，它将返回到未选中状态。

我遇到运行时错误。调试器显示它因NSException类型的未捕获异常而终止。

哪里出错了？

复选框的代码

import UIKit

class CheckBox: UIButton {

    //Images
    let checkedImage = UIImage(named: "checked")
    let unCheckedImage = UIImage(named: "unchecked")

    //bool property
    var isChecked:Bool = false {
        didSet {
            if isChecked == true{
                self.setImage (checkedImage, forState: .Normal)
            }
            else {
                self.setImage(unCheckedImage, forState: .Normal)
            }
        }
    }

    override func awakeFromNib() {
        self.addTarget(self, action: "buttonClicked", forControlEvents: UIControlEvents.TouchUpInside)
        self.isChecked = false
    }

    func buttonClicked(sender:UIButton) {
        if(sender == self) {
            if isChecked == true {
                isChecked = false
            } else {
                isChecked = true
            }
        }
    }
}

Answer 1

如果要使用所选属性，则可以执行以下操作：

class CheckBox: UIButton {

//Images
let checkedImage = UIImage(named: "checked")
let unCheckedImage = UIImage(named: "unchecked")

    //bool property
    override func awakeFromNib() {
        self.addTarget(self, action: "buttonClicked", forControlEvents: UIControlEvents.TouchUpInside)

        self.setImage (checkedImage, forState: .Selected)

        self.setImage(unCheckedImage, forState: .Normal)
    }

    func buttonClicked(sender:UIButton) {
        if(sender == self) {

            self.selected = !self.selected
        }
    }
}