ViewController in other file - ios

Question

I'm a novice with Swift 2. I tried to create a UIAlertController in another file.
This is my code :
class my_view_error: UIViewController {
func my_error(my_title: String, my_message: String) {
let alertController = UIAlertController(title: my_title, message: my_message, preferredStyle: .Alert)
let OKAction = UIAlertAction(title: "OK", style: .Default) { (action) in }
alertController.addAction(OKAction)
self.presentViewController(alertController, animated: true) {}
}
}
I'm receiving a compile time error:
Warning: Attempt to present on whose view is not in the window hierarchy!
My question is, is it possible to create a ViewController in a file other than ViewController.swift?

Answer 1

You created a UIViewController subclass called my_view_error. The UIViewController method presentViewController expects self (a my_view_error) to be on the screen at the time the method is called.
Your my_error function is perfectly fine, but it should be moved to a view controller that is actually on the screen. There is no need to create a UIViewController just to present a UIAlertController. In fact, UIAlertController is a UIViewController, and does not need help from a custom view controller.
Just like with any view controller, the view controller that is presenting the alert must be on the screen in order to perform the presentation.
Each view controller may have its own .swift file. There is no need to create one for a UIAlertController, however.
Heres a version of the function that uses rootViewController on UIApplication to get the currently on-screen view controller, and then uses that to present your alert:
func my_error(my_title: String, my_message: String) {
let alertController = UIAlertController(title: my_title, message: my_message, preferredStyle: .Alert)
let OKAction = UIAlertAction(title: "OK", style: .Default) { (action) in }
alertController.addAction(OKAction)
// Uses UIApplication.sharedApplication().keyWindow!.rootViewController! instead of self
UIApplication.sharedApplication().keyWindow!.rootViewController!.presentViewController(alertController, animated: true) {}
}