Delegation in Swift - Error Cannot invoke addTarget with an argument list

Question

I'm trying to use the delegation pattern in Swift and have got the following code:

protocol NumericViewDelegate {
    func one() 
}



class NumericView: UIView {

var delegate: NumericViewDelegate?

override init(frame: CGRect) {
    super.init(frame: frame)
    var oneButton = UIButton(frame: CGRectMake(0.0, 100.0, 200.0, 100.0))
    oneButton.titleLabel?.text = "one"
    oneButton.backgroundColor = UIColor.blueColor()
    oneButton.addTarget(self.delegate!, action: "one:", forControlEvents: UIControlEvents.TouchUpOutside)
    self.addSubview(oneButton)
}

required init(coder aDecoder: NSCoder
    ) {
    super.init(coder: aDecoder)
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
override func drawRect(rect: CGRect) {
    // Drawing code
}
*/

}

But declaring self.delegate! in addTarget doesn't work. I receive the error:

Cannot invoke 'addTarget' with an argument list of type '(NumericViewDelegate, action: String, forControlEvents: UIControlEvents).

It works when declaring self in addTarget, but that's not the intended behaviour.

possible duplicate of [Passing parameters to addTarget:action:forControlEvents](http://stackoverflow.com/questions/3988485/passing-parameters-to-addtargetactionforcontrolevents) — Lord Zsolt, May 27 '15 at 09:25
The link is not related at all. It works with self as target. — user3573256, May 27 '15 at 09:26
Which class confirms to this protocol and did you set numericViewObject.delegate = self in the class which confirms to this protocol? — Amit89, May 27 '15 at 09:32
Even if it were compiling, it won't work. You tried to pass your `delegate` variable to `addTarget()` method but it's on the `init` so `delegate` will **never** be other than `nil` at this time. You probably have to rethink how you do that. — Blackus, May 27 '15 at 09:32
No argument, but it's not related to the action, because compiling works with self no matter what I define as action. But it doesn't work with self.delegate! — user3573256, May 27 '15 at 09:33

score 2 · Accepted Answer · edited Apr 01 '17 at 12:57

Change your code to:

protocol NumericViewDelegate:NSObjectProtocol {
  func one()
}

class NumericView: UIView {

  var delegate: NumericViewDelegate?

  override init(frame: CGRect) {
    var oneButton = UIButton(frame: CGRectMake(0.0, 100.0, 200.0, 100.0))
    oneButton.titleLabel?.text = "one"
    oneButton.backgroundColor = UIColor.blueColor()
    oneButton.addTarget(self.delegate!, action: "one:", forControlEvents: UIControlEvents.TouchUpOutside)
    super.init(frame: frame)
    self.addSubview(oneButton)
  }

  required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
  }
}

In this way, it will compile well, however, your delegate is nil in init - it means nothing.

Delegation in Swift - Error Cannot invoke addTarget with an argument list

1 Answers1