仅在显示导航控制器的最顶部页面时才使UINavigationBar透明吗？

Question

I have created a custom subclass of UINavigationController that has a fully transparent background, with this code in the custom class:

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(true)
    self.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: UIBarMetrics.Default)
    self.navigationBar.shadowImage = UIImage()
    self.navigationBar.translucent = true        
}

I'd like to show a semi-transparent background on the navigation bar on subsequent screens in the navigation, for example underneath the back button in a detail view. I've added the following line to the above code to create the appearance I want:

self.navigationBar.backgroundColor = UIColorFromHex(0xFFFFFF, alpha: 0.8)

UIColorFromHex is a helper function to generate UIColors.

func UIColorFromHex(rgbValue:UInt32, alpha:Double=1.0)->UIColor {
    let red = CGFloat((rgbValue & 0xFF0000) >> 16)/256.0
    let green = CGFloat((rgbValue & 0xFF00) >> 8)/256.0
    let blue = CGFloat(rgbValue & 0xFF)/256.0

    return UIColor(red:red, green:green, blue:blue, alpha:CGFloat(alpha))
}

So far, I can only make the navigation bar is transparent for all screens, or semi-transparent for all screens.

Is there a way to toggle the appearance between transparent and semi-transparent when the root screen in the navigation stack is presented?

Answer 1

Try this.

if let rootViewController = self.navigationController.viewControllers[0] as? YourClassName {
    //Code for transparent bar
} else {
   //Code for simple bar

}

Try this in viewWillAppear method of every class, where YourClassName will be the respective class name in which you put check.. Or create a separate method and call it as necessary.