重新加载视图后，UINavigationBar titleTextAttributes不会完全更新

Question

这是一个棘手的问题。

这是我演示的故事板：

“设置”屏幕将转到“我的颜色”屏幕，用户可以在该屏幕中为应用选择深色或浅色配色方案。进行更改后，我会从窗口中删除所有视图，然后重新添加它们以强制当前视图立即通过UIAppearance代理应用更改。因此导航栏的颜色和导航栏的文本颜色都会立即改变。

接下来，用户展开segue以返回“设置”屏幕。在“设置”屏幕上，已应用导航栏的新颜色。导航栏文本的新颜色也已应用。但是，在segue处于转换状态的短暂瞬间，导航栏仍然显示旧的文本颜色。转换完成后才会显示新的文本颜色。当导航栏的文本突然从旧颜色变为新颜色时，这会导致轻微但明显的视觉故障。

要在用户翻转开关时更新导航栏文本的颜色，请在“我的颜色”屏幕的视图控制器中运行以下代码。 （完整的项目代码在Github上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)
            }
        }
    }
}

除了通过外观代理更改颜色外，我还尝试通过运行此行在“设置”屏幕视图控制器的viewWillAppear和viewWillLayoutSubviews方法中明确设置颜色：

self.navigationController?.navigationBar.titleTextAttributes = [NSFontAttributeName: UIFont(name: "Avenir-Medium", size: 22)!, NSForegroundColorAttributeName: textColor]

但这会导致同样的问题。我觉得令人困惑的是，通过外观代理进行的其他更改会在不遇到此问题的情况下进行更新。只有titleTextAttributes属性会受到此问题的困扰。

我认为，当转到“我的色彩”屏幕时，iOS可能会对“设置”屏幕进行某种“快照”。然后当segue反转时，使用具有旧导航条文本颜色的“快照”，并且直到segue完成后才更新新颜色。但如果这是真的，那么为什么导航栏的barTintColor也没有遇到同样的问题呢？反向segue的处理必须有不同的方式，但我似乎无法弄明白。

有没有办法在转换发生之前将颜色更改应用于标题文本，这会影响过渡本身？

感谢您的任何见解！