Calling presentViewController from custom class

Question

I read this post and this one on how to call a presentViewController form outside a UIViewController subclass. In my case, the custom class is a subclass of NSObject. The following approach is the only one that works (from the examples I read):

UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController, animated: true, completion: nil)

My question: is there a better solution that does not rely on the appDelegate (as I understood this approach is design-wise not very neat)...

score 11 · Accepted Answer · edited Jun 20 '20 at 09:12

11

I sometimes create a utilities class to display alerts and such. What I usually do is have my methods for presenting view controllers take the current view controller as a parameter. That approach works pretty well.

EDIT:

Here is an example method from a file Utils.swift in one of my projects. It defines a class function that displays a UIAlertController alert on the current view controller:

class Utils
{
  static let sharedUtils = Utils()
  
  class func showAlertOnVC(
    targetVC: UIViewController, 
    var title: String, 
    var message: String)
  {
    title = NSLocalizedString(title, comment: "")
    message = NSLocalizedString(message, comment: "")
    let alert = UIAlertController(
      title: title, 
      message: message, 
      preferredStyle: UIAlertControllerStyle.Alert)
    let okButton = UIAlertAction(
      title:"OK",
      style: UIAlertActionStyle.Default,
      handler:
      {
        (alert: UIAlertAction!)  in
    })
    alert.addAction(okButton)
    targetVC.presentViewController(alert, animated: true, completion: nil)
  }
}

The code above defines a class Utils. Note that it does not have any base class, which is Ok in Swift.

Next it defines a public static variable sharedUtils that you can use to get access to the singleton Utils class.

Finally, it defines a class method showAlertOnVC that can be used to display a UIAlertController alert on top of the current view controller. To use showAlertOnVC you call it from the current view controller and pass self as the targetVC parameter.

edited Jun 20 '20 at 09:12

Community

1
1

answered May 10 '15 at 20:03

Duncan C

128,072
22
173
272

And what class does that utilities class subclass? – Pieter May 10 '15 at 20:14
Doesn't matter. In Objective-C, NSObject. In Swift, no base class. – Duncan C May 10 '15 at 20:22
But that is comparable to my current solution, which also has no base class. My question is how to avoid calling the AppDelegate, which I guess will still be necessary if this class does not subclass a ViewController... – Pieter May 12 '15 at 10:29
No. Create a utilities class. Put your methods in that. You can make the methods class methods if they need instance variables, or you can make the utilities class a singleton. Classes in Swift don't have to subclass anything, unlike Objective-C. – Duncan C May 12 '15 at 10:58
This seems to work! For clarity, you may consider formatting your code as code. Nevertheless, I accepted your answer... thanks! – Pieter May 13 '15 at 18:27
Yup. I tend to type code not indented, and then indent it before posting. In this case I forgot to indent the code before posting. – Duncan C May 13 '15 at 18:56
In my comment above I should have said "you can make the methods class methods if they **don't** need instance variables, or you can make the utilities class a singleton." – Duncan C Jan 16 '17 at 20:01

score 3 · Answer 2 · edited Dec 17 '15 at 10:37

This in my opinion is the easiest solution:

class Utils {
  static  func displayTheAlert(targetVC: UIViewController, title: String, message: String){
        let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction((UIAlertAction(title: "OK", style: .Default, handler: {(action) -> Void in
        })))
        targetVC.presentViewController(alert, animated: true, completion: nil)
    }
}

// then to call it

Utils.displayTheAlert(self, title: "Fout", message: "Uw bestelling is nog niet klaar")

score 2 · Answer 3 · answered Dec 24 '16 at 06:24

2

From the design point of View, it is not advisable for the model class(NSObject) to interact directly with View. It does not conform to the MVC Pattern . Avoid using UIKIT in the NSObject class.

answered Dec 24 '16 at 06:24

Piyush Vaish

107
8

Calling presentViewController from custom class

3 Answers3

EDIT: