执行segue后，嵌入式导航栏在iOS 7（小屏幕尺寸）上消失，但不会消失iOS 9（大屏幕）

Question

I have a show segue called showPage from a view controller to a table view controller and am calling performSegueWithIdentifier() to get it to show after clicking OK on a button in an alert:

@IBAction func enterManuallyTap(sender: AnyObject) {
    var code : String!
    if #available(iOS 8.0, *) {
        let alert = UIAlertController(title: "Enter code", message: "Please enter code", preferredStyle: UIAlertControllerStyle.Alert)
        alert.addTextFieldWithConfigurationHandler({ (input:UITextField) in
            input.placeholder = "your code"
        });
        alert.addAction(UIAlertAction(title: "Cancel", style: .Cancel, handler: nil))
        alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: { (_) in
            barcode = alert.textFields!.first?.text
            self.performSegueWithIdentifier("showPage", sender: self)
        }))
        presentViewController(alert, animated: true, completion: nil)
    } else {
        let alert = UIAlertView(title: "Enter code", message: "Please enter code", delegate: self, cancelButtonTitle: "Cancel", otherButtonTitles: "OK")
        alert.alertViewStyle = UIAlertViewStyle.PlainTextInput
        alert.show()
    }
}

func alertView(alertView: UIAlertView, clickedButtonAtIndex buttonIndex: Int) {
    if buttonIndex == 1 {
        var code : String!
        code = alertView.textFieldAtIndex(0)?.text
        self.performSegueWithIdentifier("showPage", sender: self)
    }
}

This all works perfectly on my iOS 9 device, but when I try it on an iOS 7 device, the navigation bar disappears, so I can't see the title or click 'back'. The table view therefore starts at the very top of the screen and runs into the status bar.

I have tried changing the top bar from inferred to Translucent Navigation Bar and set nagivationBarHidden to false

    self.navigationController?.navigationBarHidden = false

but it still doesn't appear on iOS 7.

I just tried print(self.navigationController) in viewDidAppear() for the tableviewcontroller, and on my iOS 7 device, it prints nil , but on my iOS 9 device, it shows the controller: Optional(<UINavigationController: 0x12504e600>) ! Why does it not exist on the older device? I've seen that the navigation controller won't exist if you have a modal segue, but I'm doing a normal show segue, and I can't understand why it should work on one device but not the other.

Why does this happen, and why only on iOS 7 (or a smaller size device)?

Could this be because the iOS 9 device I'm using has a larger screen? (It's an iPhone 6S) but the iOS 7 device is an iPhone 4, which has a smaller screen. How do I go about debugging this to check whether it is a matter of screen size? However, none of the cells in the table view controller the segue goes to are cut off in any way on either device.

My storyboard (click for bigger image):

The problematic segue is the one between the 'Scan' view controller and the choose scan view controller.

Answer 1

I think the problem is with your showSegue ( showPage )

From apple developer

Show (Push)

This segue displays the new content using the showViewController:sender: method of the target view controller. For most view controllers, this segue presents the new content modally over the source view controller. Some view controllers specifically override the method and use it to implement different behaviors. For example, a navigation controller pushes the new view controller onto its navigation stack.

Make sure your first viewController is embedded into a UINavigationController in Storyboard . Make the navigationController initialViewController if your first viewController is the initialViewController . Or else it could present the new viewController modally . That means no navigationBar on top of the new viewController . I think this is happening in your case.

You can also try delete and recreate a new segue. See this:
'Show' segue in Xcode 6 presents the viewcontroller as a modal in iOS 7