How to update UI in swift from a method

Question

I am new to swift, I am writing an app which needs to change images in the storyboard. i have written a function to change images in the image view. In the function there is an if condition the image should be changed when the if condition is satisfied, but i got "unexpectedly found nil while unwrapping optional value" error when if condition is executed.

   import UIKit
   import MessageUI
   import Foundation
   import CoreLocation
    class ViewController: UIViewController {

   @IBOutlet var F_IMG: UIImageView!
   @IBOutlet var FL_IMG: UIImageView!
   @IBOutlet var FR_IMG: UIImageView!


   override func viewDidLoad() {
    super.viewDidLoad()

    TimeService.initial(viewcontroller: self)

    }

    public func showImages(){

       var type: String = Otherclass.gettype()

      setImageForType(type:type)


      }


      public  func setImageForType(type:String){

        if (type == "NONE"){

              DispatchQueue.main.async {

            self.F_IMG.image = UIImage(named: "r_f")

        }

"The showImage() function is called in another class."

I have the image in the bundle, but my UI is not getting updated and it always shows the error "unexpectedly found nil while unwrapping optional value"

Go through my answer again, if it still does not work then show how you have initialised FrontImg. — Arpit Dongre, Dec 01 '16 at 17:25
So you're calling showImages() from other class. Try replacing self.F_IMG.image to ViewController.F_IMG.image & let me know if it works. — Arpit Dongre, Dec 02 '16 at 10:10

score 2 · Accepted Answer · edited May 23 '17 at 12:10

Make sure FrontImg is properly connected to Storyboard or correctly initialised through code.

Update:

As it turns out, you're calling showImages() from other class, hence it is giving nil error.

By calling ViewController.showImages() from other class, you are creating a new ViewController, not referencing an existing one. This new one doesn't have a F_IMG(imageView) yet because its view hasn't been built. You reference self.F_IMG.image is nil.

My advice is to use NSNotificationCenter for updating UI in other View Controller.

For more approaches, refer this SO Answer

score 0 · Answer 2 · answered Dec 01 '16 at 17:20

0

I believe the problem was caused in this line :

self.FrontImg.image = UIImage(named: "r_f")

If you check the Apple Docs on UIImage class, the initializer you are using init?(named name: String) actually returns optional.

So, have you tried

self.FrontImg.image = UIImage(named: "r_f")!

answered Dec 01 '16 at 17:20

Vexy

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Still it is crashing – Mithun Sreekumar Dec 02 '16 at 08:55

Sanoj Kashyap · Answer 3 · 2016-12-01T18:32:31.530

0

The only thing here which I have found to make sure your UIElement FrontImg must be connected properly.

edited Dec 01 '16 at 18:32

answered Dec 01 '16 at 17:33

Sanoj Kashyap

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How does it help? – Arpit Dongre Dec 01 '16 at 17:43
I have added the explanation, hope it will help you. – Sanoj Kashyap Dec 01 '16 at 17:45
1

I am aware of the concept of Optionals in Swift, I'm just curious how does it help to add "!" ahead of FrontImg. If it needed force unwrap, it wouldn't have complied in the first place. – Arpit Dongre Dec 01 '16 at 17:48
As the error tells as it's nil so we have to make optional so that we added, is that make sense? – Sanoj Kashyap Dec 01 '16 at 17:51
No, it still does not make any sense to me at least. – Arpit Dongre Dec 01 '16 at 17:54
It simply wouldn't have compiled if FrontImg needed an "!". The nil error is most probably because either FrontImg isn't connected to Storyboard properly or he left some value nil. – Arpit Dongre Dec 01 '16 at 17:59
As probably this is FrontImage IBOutlet connection, so error will have chance to unconnected UIElement object usage. so marking to option will make safer. now make sense? – Sanoj Kashyap Dec 01 '16 at 18:00
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/129562/discussion-between-arpit-dongre-and-sandy). – Arpit Dongre Dec 01 '16 at 18:02

How to update UI in swift from a method

3 Answers3