swift - customised button that terminate when pressed

Question

I am trying to create a customised UIButton. This customised button shows an unchecked box which will turn into a checked box, when the user presses the button. It will then return back to unchecked when user presses the checked box.

I have a runtime error. Debugger shows that it terminates because of an uncaught exception of type NSException.

Where does it goes wrong?

Code for the checked box

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

If you want to use selected attribute then you can do the following:

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
        }
    }
}