Passing functions as parameters in Swift

Question

I have the following function working as I expect, in iOS 8:

func showConfirmBox(msg:String, title:String,
    firstBtnStr:String,
    secondBtnStr:String,
    caller:UIViewController) {
        let userPopUp = UIAlertController(title:title,
            message:msg, preferredStyle:UIAlertControllerStyle.Alert)
        userPopUp.addAction(UIAlertAction(title:firstBtnStr, style:UIAlertActionStyle.Default,
            handler:{action in}))
        userPopUp.addAction(UIAlertAction(title:secondBtnStr, style:UIAlertActionStyle.Default,
            handler:{action in}))
        caller.presentViewController(userPopUp, animated: true, completion: nil)
}

I would like to make something like the following, in order to pass as arguments the methods to be executed when one or the other of the buttons are going to be touched:

func showConfirmBox(msg:String, title:String,
    firstBtnStr:String, firstSelector:Selector,
    secondBtnStr:String, secondSelector:Selector,
    caller:UIViewController) {
        let userPopUp = UIAlertController(title:title,
            message:msg, preferredStyle:UIAlertControllerStyle.Alert)
        userPopUp.addAction(UIAlertAction(title:firstBtnStr, style:UIAlertActionStyle.Default,
            handler:{action in caller.firstSelector()}))
        userPopUp.addAction(UIAlertAction(title:secondBtnStr, style:UIAlertActionStyle.Default,
            handler:{action in caller.secondSelector()}))
        caller.presentViewController(userPopUp, animated: true, completion: nil)
}

Obviously I am not doing the right thing with firstSelector and secondSelector, because what I have tried up to now did not work. I suppose I am not using the right syntax for what I want, but I am sure it is possible to do what I would like to do. Any idea of the way to do it properly?

Answer 1

Oneword answer for your question is Closures

The Default Syntax for closures is () -> ()

Instead of Selector you could directly mention the method definition

func showConfirmBox(msg:String, title:String,
    firstBtnStr:String, firstSelector:(sampleParameter: String) -> returntype,
    secondBtnStr:String, secondSelector:() -> returntype,
    caller:UIViewController) {
    //Your Code
}

But using this will create readability problems so i suggest you to use typeAlias

typealias MethodHandler1 = (sampleParameter : String)  -> Void
typealias MethodHandler2 = ()  -> Void

func showConfirmBox(msg:String, title:String,
                    firstBtnStr:String, firstSelector:MethodHandler1,
                    secondBtnStr:String, secondSelector:MethodHandler2) {

    // After any asynchronous call
    // Call any of your closures based on your logic like this
    firstSelector("FirstButtonString")
    secondSelector()
}

You can call your method like this

func anyMethod() {
   //Some other logic 

   showConfirmBox(msg: "msg", title: "title", firstBtnStr: "btnString", 
         firstSelector: { (firstSelectorString) in
              print(firstSelectorString) //this prints FirstButtonString
         }, 
         secondBtnStr: "btnstring") { 
           //Invocation comes here after secondSelector is called

         }
}