iOS unrecognized selector sent to instance in Swift

Question

I am having problems with trying to get a UIButton to work when the user presses it. I keep getting an error saying: unrecognised selector sent to instance

override func viewDidLoad() {
    super.viewDidLoad()

    button.addTarget(self, action: "buttonClick", forControlEvents: UIControlEvents.TouchUpInside)
    button.setTitle("Print", forState: UIControlState.Normal)
    button.font = UIFont(name: "Avenir Next", size: 14)
    button.backgroundColor = UIColor.lightGrayColor()
    self.view.addSubview(button)
}

func buttonClick(Sender: UIButton!)
{
    myLabelInfo.text = "Hello"
}

For a Swift method such as func buttonClick(Sender: UIButton) what is the correct string to pass to addTarget method for the selector? Is it "buttonClick", "buttonClick:", "buttonClickSender:" or something else?

Answer 1

You're using an invalid method signature for the action. You're supplying buttonClick, but the method has an argument, so the signature should be buttonClick:

button.addTarget(self, action: "buttonClick:", forControlEvents: UIControlEvents.TouchUpInside)

For more information about how to format your selectors, you can refer to the accepted answer in the post linked below. The code used in this post may be Objective-C, but all its lessons can be applied here as well.

Creating a selector from a method name with parameters

And as a side note, this code would also be valid if you used Selector("buttonClicked:") as the action, but you don't have to because string literals can be implicitly cast to the Selector type.

Quoting from Using Swift with Cocoa and Objective-C

An Objective-C selector is a type that refers to the name of an Objective-C method. In Swift, Objective-C selectors are represented by the Selector structure. You can construct a selector with a string literal, such as let mySelector: Selector = "tappedButton:". Because string literals can be automatically converted to selectors, you can pass a string literal to any method that accepts a selector.