Change UIScrollView Offset to top from another viewController in Swift 4

Question

I have mainViewController and inside have scrollView and I have secondViewController I want to change scrollView offset to top from secondViewController when I want to try it with NSNotificationCenter gives me ;

: unrecognized selector sent to instance 0x7ff83e024200'

How can I fix it ? My codes under below.

mainViewController

       override func viewDidLoad() {
            super.viewDidLoad()

            NotificationCenter.default.addObserver(self, selector: "gotop:", name: NSNotification.Name(rawValue: "gotop"), object: nil)

    }

  func gotop(){
         scrollView.setContentOffset(CGPoint(x:0, y:0), animated: false)
    }

secondViewController

@IBAction func goButton (sender : UIButton){

        NotificationCenter.default.post(name: NSNotification.Name(rawValue: "gotop"), object: nil)


    }

https://stackoverflow.com/questions/24049020/nsnotificationcenter-addobserver-in-swift — Subin K Kuriakose, Nov 07 '17 at 08:42

score 2 · Answer 1 · answered Nov 07 '17 at 08:48

2

I have used below code in my project to add notification :

NotificationCenter.default.addObserver(self, selector: #selector(YourViewController.gotop), name: NSNotification.Name(rawValue: "gotop"), object: nil)

Try if it works in your scenario.

answered Nov 07 '17 at 08:48

Amit

4,837
5
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Suhit Patil · Accepted Answer · 2017-11-07T11:04:15.267

2

check your addObserver code, selector should have below signature

NotificationCenter.default.addObserver(self, selector: #selector(MainViewController.goTop(notification:)), name: Notification.Name("gotop"), object: nil)

Method handler for received Notification:

func goTop(notification: Notification){
   scrollView.setContentOffset(CGPoint(x:0, y:0), animated: false)
}

For posting notification

NotificationCenter.default.post(name: Notification.Name("gotop"), object: nil)

Remove Notification in denit

deinit {
  NotificationCenter.default.removeObserver((self, name: Notification.Name("gotop"), object: nil)
}

edited Nov 07 '17 at 11:04

answered Nov 07 '17 at 08:51

Suhit Patil

11,748
3
50
60

Great it worked. Don't forget to remote notification in deinit method – Suhit Patil Nov 07 '17 at 09:04
what is in deinit ? I need to add extra coding ? – SwiftDeveloper Nov 07 '17 at 09:42
where can i put denit code ? after posting notification ? – SwiftDeveloper Nov 07 '17 at 11:18
same file where you have added observer, in MainViewController – Suhit Patil Nov 07 '17 at 12:40

score 1 · Answer 3 · answered Nov 07 '17 at 08:44

1

the definition of your "goTop" func is wrong :

instead of

func gotop(){
  //do your stuff
}

try this :

func gotop(notification : NSNotification){
   //do your stuff
}

let me know if this solve your problem.

answered Nov 07 '17 at 08:44

Leonardo

218
4
17

trying I will let – SwiftDeveloper Nov 07 '17 at 08:46

Change UIScrollView Offset to top from another viewController in Swift 4

3 Answers3