How do I pass more parameters to a UIAlertAction's handler? - ios

Question

Is there any way to pass the array "listINeed" to the handler function "handleConfirmPressed"? I was able to do this by adding it as a class variable but that seemed very hacky and now I want to do this for multiple variables so I need a better solution.
func someFunc(){
//some stuff...
let listINeed = [someObject]
let alert = UIAlertController(title: "Are you sure?", message: alertMessage, preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction(UIAlertAction(title: "Cancel", style: .Cancel, handler: nil))
alert.addAction(UIAlertAction(title: "Confirm", style: .Destructive, handler: handleConfirmPressed))
presentViewController(alert, animated: true, completion: nil)
}
func handleConfirmPressed(action: UIAlertAction){
//need listINeed here
}

Answer 1

The easiest way is to just pass a closure to the UIAlertAction constructor:
func someFunc(){
//some stuff...
let listINeed = [ "myString" ]
let alert = UIAlertController(title: "Are you sure?", message: "message", preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction(UIAlertAction(title: "Cancel", style: .Cancel, handler: nil))
alert.addAction(UIAlertAction(title: "Confirm", style: .Destructive, handler:{ action in
// whatever else you need to do here
print(listINeed)
}))
presentViewController(alert, animated: true, completion: nil)
}
If you really want to isolate the functional part of the routine, you can always just put:
handleConfirmPressedAction(action:action, needed:listINeed)
into the callback block
A slightly more obscure syntax, that would retain the feel of a function both in passing it to the completion routine and in the callback function itself would be to define handleConfirmPressed as a curried function:
func handleConfirmPressed(listINeed:[String])(alertAction:UIAlertAction) -> (){
print("listINeed: \(listINeed)")
}
and then you can addAction using:
alert.addAction(UIAlertAction(title: "Confirm", style: .Destructive, handler: handleConfirmPressed(listINeed)))
Note that the curried function is shorthand for:
func handleConfirmPressed(listINeed:[String]) -> (alertAction:UIAlertAction) -> () {
return { alertAction in
print("listINeed: \(listINeed)")
}
}

Answer 2

I think this is easier.
class MyUIAlertAction: UIAlertAction {
var params: [String: Any] = [:]
}
func someFunc(){
//some stuff...
let listINeed = [ "myString" ]
let alert = UIAlertController(title: "Are you sure?", message: "message", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
let action = MyUIAlertAction(title: "Confirm", style: .destructive, handler:{ (action: UIAlertAction) in
if let myaction = action as? MyUIAlertAction {
let listINeed = myaction.params["listINeed"] as? [String] ?? []
// whatever else you need to do here
print(listINeed)
}
})
action.params["listINeed"] = listINeed
alert.addAction(action)
}