展开控制器中的导航控制器清除

Question

I have a segue connecting two views. In the parent view, the navigation bar is a gray color, and in the child view, it's clear. When unwinding the segue, the navigation bar in the parent controller is now clear as well. How to fix this?

Parent Controller

  override func viewWillAppear(animated: Bool) {
    self.navigationItem.title = "FEED"
    self.navigationController?.navigationBar.barTintColor = UIColor(white:0.97, alpha:1.0)
    let navBarLineView = UIView(frame: CGRectMake(0,
        CGRectGetHeight((navigationController?.navigationBar.frame)!),
        CGRectGetWidth((self.navigationController?.navigationBar.frame)!),
        1))
    navBarLineView.backgroundColor = UIColor(red:0.91, green:0.91, blue:0.92, alpha:1.0)
    navigationController?.navigationBar.addSubview(navBarLineView)
}

Child Controller

 override func viewWillAppear(animated: Bool) {
    self.navigationItem.title = "Space
    self.navigationController?.navigationBar.barTintColor = UIColor.whiteColor()

    navigationController!.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: UIBarMetrics.Default)
    navigationController!.navigationBar.shadowImage = UIImage()
    navigationController!.navigationBar.translucent = true
}

Answer 1

Setting background and shadow images to nil in viewWillDisappear method in the child controller worked fine for me when I wanted to restore default style of navigation bar:

override func viewWillDisappear(animated: Bool) {
    navigationController!.navigationBar.setBackgroundImage(nil, forBarMetrics: UIBarMetrics.Default)
    navigationController!.navigationBar.shadowImage = nil
}