Presenting view controllers on detached view controllers is discouraged - screen view turns black

Question

I have two view controllers: VC1 and VC2. From VC1, press a button will navigate app to VC2. VC2 has a network request function in viewDidLoad() which shows an alert if the request is failed.

If everything is fine, no request failure on VC2, when I move back to VC1, it would call to deinit function of VC2.

However, if the request failed and an error alert is shown, the deinit function (of VC2) wouldn't be called when I move back VC1. Moreover, it causes an error of "Presenting view controllers on detached view controllers is discouraged" while it's trying to show that alert after the screen displays VC1, screen then turns black except for navigation bar and the error alert of VC2 is shown on VC1 (The reason is when the VC2 is going to present the error alert, user suddenly press the back button on navigation bar to move back to previous screen). My alert is a global variable.

Here is the code I handle request and show alert on VC2:

func sendRegisterRequest() {
    registerAPI.request(parameters: parameters) {
        [weak self] (response) in

        if let strongSelf = self {
            strongSelf.handleResponse(response)
        }
    }
}

func handleResponse(response: Response<AnyObject, NSError>) {
    let result = ResponseHandler.responseHandling(response)

    if result.messageCode != MessageCode.Success {
        // Show alert
        handleResponseError(LocalizedStrings.registerFailedTitle, message: result.messageInfo, requestType: .Register)
        return
    }
}

func handleResponseError(title: String, message: String?, requestType: RequestType?) {
    alert = UIAlertController(title: title, message: message, preferredStyle: .Alert)
    let action = UIAlertAction(title: LocalizedStrings.okButton, style: UIAlertActionStyle.Default) { (action) -> Void in
        self.handleAlertViewAction(requestType)
    }

    alert.addAction(action)

    dispatch_async(dispatch_get_main_queue(), {
        self.presentViewController(self.alert, animated: true, completion: nil)
    })
}

I attach the screenshot here:

Could anyone have solution for this issue? Any help could be appreciated,

Lucy Nguyen.

I think you are presenting alert on VC2 and then dismissing VC2. You should dismiss VC2 on tapping the OK button. OR you should dismiss VC2 and then display the alert — san
The alert is shown depends on the request result. And when the VC2 is going to present the alert, user suddenly press the back button on navigation bar to move back to previous screen. That causes this error. — Lucy
I call deinit function to know does the VC2 get deinit or not, if yes the alert is released. Let me add some code. — Lucy

Mijeong.J Mijeong.J · Accepted Answer · 2016-06-22T12:26:38

I've got the same problem when I build my app. To solve this problem, I tried many changes and finally removed the error message.

I made an alert window in first VC to give user some notice. And I write the alert control code in - (void)viewDidLoad. I think you did it same or in - (void)viewWillAppear.

Just move your alert code to - (void)viewDidAppear. Then, error will be gone.

Presenting view controllers on detached view controllers is discouraged - screen view turns black

1 Answers