Navigation Bar Jumping After Transition - ios

Question

I am making an app that uses a tab bar to navigate between view controllers. I wanted to add a transition effect that would cross dissolve between each view when a tab button was pressed. I have implemented this transition with UIView.transitionFromView, however the navigation bar is not working as expected during the transition. During a transition to a view for the first time, the navigation bar is displayed too high, but jumps back into place once the transitions is complete. However, the next time you switch to the same view, the navigation bar is in the correct place during and after the transition.
I have seen an answer here to fix the problem for a custom animation, but I could not figure out how to get it to work with my current implementation.
MY Question
I have seen answers fixing the issue by forcing the view down by a few points (44 points), but is there a way to do it without directly changing the points? This might work the first time, but the issue resolves itself when any view is transitioned to a second time, thus making the view too low if you change the points.
Here is my code for the tab bar controller and the transition:
import UIKit
class MainTabBarViewController: UITabBarController, UITabBarControllerDelegate {
override func viewDidLoad() {
super.viewDidLoad()
self.delegate = self
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
// Method used to detect when a tab bar button has been tapped
func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
// Creating the 'to' and 'from' views for the transition
let fromView = tabBarController.selectedViewController!.view
let toView = viewController.view
if fromView == toView {
// If views are the same, then don't do a transition
return false
}
self.view.userInteractionEnabled = false
UIView.transitionFromView(fromView, toView: toView, duration: 2.0, options: .TransitionCrossDissolve, completion: nil)
self.view.userInteractionEnabled = true
return true
}
}
And here is what the issue looks like:

Answer 1

You can try with this code:
import UIKit
class MainTabBarViewController: UITabBarController, UITabBarControllerDelegate {
override func viewDidLoad() {
super.viewDidLoad()
self.delegate = self
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
// Method used to detect when a tab bar button has been tapped
func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
// Creating the 'to' and 'from' views for the transition
let fromView = tabBarController.selectedViewController!.view
let toView = viewController.view
if fromView == toView {
// If views are the same, then don't do a transition
return false
}
self.view.userInteractionEnabled = false
if let window = fromView.window {
let overlayView = UIScreen.mainScreen().snapshotViewAfterScreenUpdates(false)
viewController.view.addSubview(overlayView)
UIView.transitionFromView(fromView, toView: toView, duration: 2.0, options: .TransitionCrossDissolve, completion: { (finish) in
window.rootViewController = viewController
UIView.animateWithDuration(0.4, delay: 0.0, options: .TransitionCrossDissolve, animations: {
overlayView.alpha = 0
}, completion: { (finish) in
overlayView.removeFromSuperview()
})
})
}
self.view.userInteractionEnabled = true
return true
}
}

Answer 2

In my case, call toView.layoutIfNeeded() before the transition fixed the issue.