iOS Swift3 check nil value for ViewController Object

Question

let viewControllers: [UIViewController] = self.navigationController!.viewControllers

for VC  in viewControllers  {            
    if (VC.isKind(of: HomeViewController.self)) {            
         bScreen = true
         self.navigationController?.popToViewController(VC, animated: true)
     }
}

if bScreen == false {
    let homeVC = HomeViewController()
    self.navigationController?.pushViewController(homeVC, animated: false)
}

I loop through navigation controller array to move to HomeViewController.above code is working fine.some times i am getting crash as “fatal error: unexpectedly found nil while unwrapping an Optional value”.I know the cause for this crash.Please help me how to check nil value for view controller object.any help will be appreciated.thanks in advance

yes..it is crashing at "self.navigationController?.popToViewController(VC, animated: true)" this line — arun rajesh, Mar 01 '17 at 04:52
Possible duplicate of [Using isKindOfClass with Swift](http://stackoverflow.com/questions/24019707/using-iskindofclass-with-swift) — Harshal Valanda, Mar 01 '17 at 04:55
@arunrajesh I don't think it can be possible because If vc is nil then it does not go inside the if statement. Try wth `is` instead of `kindOf` swift changed its syntax. — dahiya_boy, Mar 01 '17 at 05:01

score 2 · Answer 1 · answered Mar 01 '17 at 04:59

2

-- Swift 3 --

for vc in (self.navigationController?.viewControllers)! {
     if vc is HomeViewController {
        _ = self.navigationController?.popToViewController(vc, animated: true)
     }
}

answered Mar 01 '17 at 04:59

Harshal Valanda

5,331
26
63

score 1 · Accepted Answer · answered Mar 01 '17 at 04:58

1

Use this code. this is helpful for you.

let viewControllers: [UIViewController] = self.navigationController!.viewControllers
            for VC  in viewControllers  {
                if (VC.isKind(of: HomeViewController.self)) {
                    bScreen = true
                    self.navigationController?.popToViewController(VC, animated: true)
                    break;
                }
            }

            if bScreen == false
            {
                let homeVC = HomeViewController()
                self.navigationController?.pushViewController(homeVC, animated: false)
            }

answered Mar 01 '17 at 04:58

Brijesh Shiroya

3,323
1
13
20

This code is no different from the original code, Please add explanation why do you think it will work – Varun Naharia Mar 01 '17 at 05:02
@VarunNaharia .please see it carefully i adding break in code – Brijesh Shiroya Mar 01 '17 at 05:03
1

I know, but you should type it in the answer, and not just paste code, and if you carefully review your code it has no functional changes there it will work exactly same as original – Varun Naharia Mar 01 '17 at 05:04
@VarunNaharia. no whenver you running this code it sometimes crash. but if u add break then breaking the loop and no crashes happen. – Brijesh Shiroya Mar 01 '17 at 05:08

Parth Adroja · Answer 3 · 2017-03-01T05:05:38.867

1

Never use directly ! until you are damn sure that it will not be nil. Replace your code as below. You can use if let or guard let to unwrap optionals.

    if let viewControllers: [UIViewController] = self.navigationController?.viewControllers {
                for VC  in viewControllers  {

                    if (VC.isKind(of: ViewController.self)) {

                        bScreen = true
                        self.navigationController?.popToViewController(VC, animated: true)
                    }
                }

                if bScreen == false
                {
                    let homeVC = ViewController()
                    self.navigationController?.pushViewController(homeVC, animated: false)
                }
 } 
else {
     // IF VC is nil
}

edited Mar 01 '17 at 05:05

answered Mar 01 '17 at 05:02

Parth Adroja

13,198
5
37
71

where is the else part of if let it will work differently from the original requirement – Varun Naharia Mar 01 '17 at 05:03
Else part is not required I guess but still depends on the code. – Parth Adroja Mar 01 '17 at 05:04
1

@VarunNaharia if let condition is not contains else part. please check if let condition documentation – Brijesh Shiroya Mar 01 '17 at 05:05
@VarunNaharia That else part is not required but if someone wants to add then it can be achieved like above. – Parth Adroja Mar 01 '17 at 05:07

score 1 · Answer 4 · answered Mar 01 '17 at 05:04

let getCurrentVCIndex = self.navigationController?.viewControllers.indexOf({ (viewController) -> Bool in

if let _ = viewController as? HomeViewController {
    return true
}
return false
})


if  getCurrentVCIndex
 {
let HomeVC = self.navigationController?.viewControllers[getCurrentVCIndex!] as! HomeViewController

self.navigationController?.popToViewController(HomeVC, animated: true)
}
else
  {
 // use push
}

or use like

if  let  HomeVC =  self.navigationController?.viewControllers.filter({$0 is HomeViewController}).first
{
self.navigationController?.popToViewController(HomeVC!, animated: true)
}else
{
  // use push
}

Anuraj · Answer 5 · 2017-03-01T05:07:16.040

0

This is better to use to if let / guard for an optional value to avoid crashing.

if let viewControllers: [UIViewController] = self.navigationController.viewControllers{

        for VC  in viewControllers  {

            if (VC.isKind(of: HomeViewController.self)) {

                bScreen = true
                self.navigationController?.popToViewController(VC, animated: true)
            }
        }

if bScreen == false
        {
            let homeVC = HomeViewController()
            self.navigationController?.pushViewController(homeVC, animated: false)
        }
}

edited Mar 01 '17 at 05:07

answered Mar 01 '17 at 04:56

Anuraj

1,242
10
25

1

Add some explanation to your answer, not only a code snippet. – Mar 01 '17 at 04:57
Just added a if let check for navigationController to make sure it is not nil – Anuraj Mar 01 '17 at 04:59
2

I know, but you should type it in the answer, and not just paste code. – Mar 01 '17 at 05:00

score 0 · Answer 6 · answered Mar 01 '17 at 05:07

Based on your code, In the loop, if the navigation stack contains the respective view controller will be popped to the respective page. But the thing is if the same view controller is present two times, will lead to execute the loop for the same time. This may cause crash. So Add a break after the poptoviewcontroller will avoid this issue. Please check the below code, will help you.

 if (VC.isKind(of: HomeViewController.self)) {

                bScreen = true
                self.navigationController?.popToViewController(VC, animated: true)
                break
            }

iOS Swift3 check nil value for ViewController Object

6 Answers6

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