Swift;Casting custom viewcontroller to viewcontroller

Question

I have a struct that handles alerts for me. It just has one function:

func presentAlert(_ title:String, _ message:String, _ presenter:ViewController) {

        let myAlert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
        myAlert.addAction(okAction)
        presenter.present(myAlert, animated:true, completion:nil)
    }

I can call this fine from the viewcontroller. But on a subclass, AddTopicViewController I am getting an error:

myController.alert.presentAlert("Form errors", strErrMsg, self)

//error from compiler
Cannot convert value of type 'AddTopicViewController' to expected argument type 'ViewController'

So, two questions:

Since AddTopicVC is a subclass of VC I thought it would pass through for something requiring a VC. Obviously wrong on that one. Could someone explain the flaw in my logic on that?

Any suggestions on how to accomplish my goal? The app has a lot of validation and alerts are presented whenever the user hasn't entered required data, but all the viewcontrollers are subclass. I tried extending viewcontroller with the function but the subclasses gave an error that the method wasn't available.

Thanks for the help.

Where is defined AddTopicViewController? I'd tend to say/guess that's it's inherited from UIViewController, not ViewController. — Larme
– Larme, Commented Nov 2, 2017 at 16:14

vadian · Accepted Answer · 2017-11-02 16:15:16Z

1

The easiest way is to use the presumed base class, UIViewController, which all view controllers inherit from.

func presentAlert(_ title:String, _ message:String, _ presenter:UIViewController)

Alternatively use an extension of UIViewController

extension UIViewController {

    func presentAlert(_ title:String, _ message:String) {

        let myAlert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
        myAlert.addAction(okAction)
        present(myAlert, animated:true, completion:nil)
    }

}

answered Nov 2, 2017 at 16:15

vadian

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1 Comment

PruitIgoe Over a year ago

Ah, I see where I fell off the rails. Thanks!

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