ios - 导航栏外观在第一次设置后不会改变

Question

当应用程序激活时，我为导航栏的标题设置了一定的垂直偏移量:

[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-3.0f forBarMetrics:UIBarMetricsDefault];

然后，在导航层次结构的后面，我需要设置一个不同的垂直偏移量，所以我调用:

[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:-0.5f forBarMetrics:UIBarMetricsDefault];

但我发现当我在应用程序处于事件状态的情况下导航时，新的垂直偏移并未应用。但是，如果应用程序变为非事件状态然后再次事件，则会应用它。当应用程序保持在前台时，如何更改此偏移量？

谢谢!

Answer 1

来自 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.

所以基本上你需要做一些 HACK 来删除 View ，然后立即将其添加回来，就像这样......

UIView *currentview = ((AppDelegate*)[UIApplication sharedApplication].delegate).window.rootViewController.view;
UIView *superview = currentview.superview;
[currentview removeFromSuperview];
[superview addSubview:currentview];

对于 Swift...

if let currentview = (UIApplication.sharedApplication().delegate as? AppDelegate)?.window?.rootViewController?.view {
    if let superview = currentview.superview {
        currentview.removeFromSuperview()
        superview.addSubview(currentview)
    }
}