Swift: Passing a parameter to selector

Question

Using Swift 3, Xcode 8.2.1

Method:

func moveToNextTextField(tag: Int) {
   print(tag)
}

The lines below compile fine, but tag has an uninitialized value:

let selector = #selector(moveToNextTextField)
Timer.scheduledTimer(timeInterval: 0.2, target: self, selector: selector, userInfo: nil, repeats: false)

However, I need to pass a parameter. Below fails to compile:

let selector = #selector(moveToNextTextField(tag: 2))

Swift Compile Error:
Argument of #selector does not refer to an @objc method, property, or initializer.

How can I pass an argument to a selector?

Answer 1

#selector describes method signature only. In your case the correct way to initialize the selector is

let selector = #selector(moveToNextTextField(tag:))

Timer has the common target-action mechanism. Target is usually self and action is a method that takes one parameter sender: Timer. You should save additional data to userInfo dictionary, and extract it from sender parameter in the method:

func moveToNextTextField(sender: Timer) {
   print(sender.userInfo?["tag"])
}
...
let selector = #selector(moveToNextTextField(sender:))
Timer.scheduledTimer(timeInterval: 0.2, target: self, selector: selector, userInfo: ["tag": 2], repeats: false)

Answer 2

You cannot pass a custom parameter through a Timer action.

Either

#selector(moveToNextTextField)
...
func moveToNextTextField()

or

#selector(moveToNextTextField(_:))
...
func moveToNextTextField(_ timer : Timer)

is supported, nothing else.

To pass custom parameters use the userInfo dictionary.