Why is the button that triggers an unwind segue instantly disappearing?

Question

I am developing an app where I use custom segues to navigate between two UIViewController.

The segue to the second UIViewController animates just fine. But when the unwind segue is triggered, the button that triggers it instantly disappears while slowly animating the rest just fine.

The Button is set up via Storyboard and I ctrl-dragged from it to the Exit of that UIViewController. An unwind segue showed up and I set up all the necessary files.

I assign my custom class to the Unwind segue and now override the perform()-method like so:

override func perform() {

    let settingsVCView = self.sourceViewController.view
    let startVCView = self.destinationViewController.view

    let screenHeight = UIScreen.mainScreen().bounds.size.height
    let screenWidth = UIScreen.mainScreen().bounds.size.width

    let window = UIApplication.sharedApplication().keyWindow
    window?.insertSubview(startVCView, aboveSubview: settingsVCView)

    UIView.animateWithDuration(0.8, delay: 0, options: .CurveEaseInOut, animations: { () -> Void in

            settingsVCView.frame = CGRectMake(0, -(screenHeight), screenWidth, screenHeight)
            startVCView.frame = CGRectMake(0, 0, screenWidth, screenHeight)

        }) { (finished) -> Void in

            self.sourceViewController.dismissViewControllerAnimated(false, completion: nil)

    }

}

Everything is set up and the animation is done like you can see in the gif. Some would say the animation works properly now, but the early disappearing of that button really bothers me. I tried:

• Adjusting the buttons highlighted state
• Installing the button not just in Compact/Regular
• Setting the Buttons Type from System to Custom
• Tried to trace the exact moment, the button disappears via breakpoints (couldn't find it, but found out, that setting the frames in the closure-block isn't a problem either)
• Commented out the dismissViewControllerAnimated: function

I did not find any solution.

Answer 1

I finally got the issue resolved by first clearing all the layout constraints of that Button. I then tapped it again and it didn't disappear, so it had something to do with the constraints.

This is what the constraint should be set like.

The mistake was pinning the top constraint of the button to the Top Layout Guide and not the View top. Changing this anchor resolved my problem and my Button stopped hiding :)