UINavigationBar titleTextAttributes does not update fully after reloading views - swift

Question

This is a tricky one.
Here is my storyboard for this demo:
The Settings screen segues to the My Color screen where users can choose either a dark or light color scheme for the app. When a change is made, I remove all views from the window and then re-add them to force the current view to immediately apply the changes via the UIAppearance proxy. So the color of the navigation bar and the nav bar's text color both change immediately.
Next, the user unwinds the segue to return to the Settings screen. On the Settings screen, the new color of the navigation bar is already applied. The new color of the nav bar's text is also already applied. However, for a brief instant while the segue is in transition, the nav bar still shows the old text color. The new text color is not shown until after the transition is complete. This results in a minor, but noticable, visual glitch as the nav bar's text suddenly changes from the old color to the new color.
To update the color of the nav bar text when the user flips the switch, I run the following code in the My Color screen's view controller. (The full project code up on Github at https://github.com/prinomen/social_demo2).
func switchValueDidChange(sender:UISwitch!) {
if (sender.on == true) {
colorIndex = 1 // nav bar is now black
UINavigationBar.appearance().barTintColor = black // set appearance proxy to the new color
// Run this switch to set the textColor global var to match the preferred color scheme, based on the value of colorIndex.
switch colorIndex {
case 0: // white
textColor = green
statusBarTextIsBlack = true
case 1: // black
textColor = red
statusBarTextIsBlack = false
default:
break;
}
// Update these appearance proxy items (they need the window to reload before they will manifest their changes).
UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName: UIFont(name: "Avenir-Medium", size: 22)!, NSForegroundColorAttributeName: textColor]
UINavigationBar.appearance().tintColor = textColor
// Remove all views from the window and then re-add them in order to force the current view to immediately apply changes to UIAppearance.
let windows : NSArray = UIApplication.sharedApplication().windows
for window in windows as! [UIWindow] {
for view in window.subviews {
view.removeFromSuperview()
window.addSubview(view)
}
}
} else {
colorIndex = 0 // nav bar is now white
UINavigationBar.appearance().barTintColor = white // set appearance proxy to the preferred color
// Run this switch to set the textColor global var to match the preferred color scheme, based on the value of colorIndex.
switch colorIndex {
case 0: // white
textColor = green
statusBarTextIsBlack = true
case 1: // black
textColor = red
statusBarTextIsBlack = false
default:
break;
}
// Update these appearance proxy items (they need the window to reload before they will manifest their changes).
UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName: UIFont(name: "Avenir-Medium", size: 22)!, NSForegroundColorAttributeName: textColor]
UINavigationBar.appearance().tintColor = textColor
// Remove all views from the window and then re-add them in order to force the current view to immediately apply changes to UIAppearance.
let windows : NSArray = UIApplication.sharedApplication().windows
for window in windows as! [UIWindow] {
for view in window.subviews {
view.removeFromSuperview()
window.addSubview(view)
}
}
}
}
Aside from changing the color via the appearance proxy, I've also tried setting the color explicitly within the viewWillAppear and viewWillLayoutSubviews methods of the Settings screen view controller by running this line:
self.navigationController?.navigationBar.titleTextAttributes = [NSFontAttributeName: UIFont(name: "Avenir-Medium", size: 22)!, NSForegroundColorAttributeName: textColor]
But this results in the same issue. What I find confusing is that the other changes made via the appearance proxy are updated without encountering this issue. Only the titleTextAttributes property is troubled by this issue.
I thought that maybe iOS makes some kind of "snapshot" of the Settings screen when segueing to the My Color screen. Then when the segue is reversed, the "snapshot" with the old nav bar text color is used and the new color is not updated until the segue is finished. But if that were true, then why doesn't the navigation bar's barTintColor also experience the same problem? There must be a different way the reverse segue is handled, but I can't seem to figure it out.
Is there a way to apply the color change to the title text before the transition happens, in a way that affects the transition itself?
Thanks for any insight!