Navigation bar appearance doesn't change after a first setting - ios

Question

I set a certain vertical offset for the navigation bar's title when the app becomes active:
[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-3.0f forBarMetrics:UIBarMetricsDefault];
Then, later in the navigation hierarchy, I need to set a different vertical offset, so I call:
[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-0.5f forBarMetrics:UIBarMetricsDefault];
But I find that the new vertical offset is not applied when I navigate being the app active. However, if app becomes inactive and then active again, it is applied. How can I change this offset while the app is kept in foreground?
Thanks!

Answer 1

From https://developer.apple.com/library/prerelease/ios/documentation/UIKit/Reference/UIAppearance_Protocol/index.html
iOS applies appearance changes when a view enters a window, it doesn’t
change the appearance of a view that’s already in a window. To change
the appearance of a view that’s currently in a window, remove the view
from the view hierarchy and then put it back.
So basically you need to do some HACK to remove the view and then immediately add it back, something like this...
UIView *currentview = ((AppDelegate*)[UIApplication sharedApplication].delegate).window.rootViewController.view;
UIView *superview = currentview.superview;
[currentview removeFromSuperview];
[superview addSubview:currentview];
And for Swift...
if let currentview = (UIApplication.sharedApplication().delegate as? AppDelegate)?.window?.rootViewController?.view {
if let superview = currentview.superview {
currentview.removeFromSuperview()
superview.addSubview(currentview)
}
}

Answer 2

Did you try doing this with animation block?
[UIView animateWithDuration:3
animations:^{
[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-3.0f forBarMetrics:UIBarMetricsDefault];
[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-0.5f forBarMetrics:UIBarMetricsDefault];
}];