Declaration of Handlers doesn't work - ios

Question

I've read a few examples on declaring handlers for UIAlertViews and somehow I just can't grasp the concept of the proper syntax. I've seen a few examples where they do one of the following:
- handler: someFunction
- handler: {action in SomeFunction} (what does "action in" mean?)
- handler: { _ in print("Foo!") (again, what does "in" mean?)
My biggest concern is that I don't know what these things mean. and I'm trying to use the first style however I get the following error: "Variable used within its own initial value"
let answerVCAlert = UIAlertController(title: "Your turn", message: "What's the answer?", preferredStyle: .alert)
let submitAnswer = UIAlertAction(title: "Submit", style: .default, handler: submitAnswer(answer: " ")) //grab from textfield
let noAnswer = UIAlertAction(title: "No Answer", style: .default, handler: submitAnswer(answer: " "))
func submitAnswer(answer: String) {
print ("The string passed is \(answer)")
//compare answer to correct answer
}
func attemptAnswer() {
answerVCAlert.addAction(submitAnswer)
answerVCAlert.addAction(noAnswer)
//answerVCAlert.addTextField //how ??? too many different examples
self.present(answerVCAlert, animated: true, completion: nil)
}

Answer 1

As mentioned in the comments, now's the time to learn how to using closures or completion handlers. It's time well spent.
Here's some working code (based on your's but with some minor changes) that also includes a textfield. A good Swift 3 example of getting the text from an alert textfield is this SO answer. There is a change in Swift 4 syntax in my code below.
I've indented the code in hopes it helps you understand completion handlers better. I added some inline comments also.
Here's the alert:
// I changed the name of your alert controller for brevity
let alertVC = UIAlertController(
title: "Your turn",
message: "What's the answer?",
preferredStyle: .alert)
// Add a textfield called answerText. You may not want the placeholder to be blank.
alertVC.addTextField(configurationHandler: {(answerText: UITextField!) in
answerText.placeholder = "Default answer"
})
// Add a Submit button that will call submitAnswer()
let submitAnswer = UIAlertAction(
title: "Submit",
style: .default,
handler: { action -> Void in
self.submitAnswer(alertVC.textFields![0])
})
alertVC.addAction(submitAnswer)
// Add a No Answer button that will call noAnswer()
// NOTE: I changed this to be style of cancel... check out how it's rendered.
let noAnswer = UIAlertAction(
title: "No Answer",
style: .cancel,
handler: { action -> Void in
self.noAnswer()
})
alertVC.addAction(noAnswer)
// I think you *want* everybody to try to answer, so let's make that the preferred action.
alertVC.preferredAction = submitAnswer
present(
alertVC,
animated: true,
completion: nil)
And here's the results:
func submitAnswer(_ answer: String) {
print ("The answer is \(answer)")
//compare answer to correct answer
}
func noAnswer() {
print ("Cancel was tapped.")
}
Among the changes I made are:
Changed the style of one action from .default to .cancel to give you an idea of what that does.
Added self to the completion handler calls - they are required.
Changed the signature of submitAnswer() to no longer need the parameter label. It's Swiftier that way.
Changed the noAnswer action call from submitAnswer() to noAnswer() to distinguish what the user tapped on.