extension UIViewController {
    var topbarHeight: CGFloat {
        return
            (view.window?.safeAreaInsets.top ?? 0) +
            (view.window?.windowScene?.statusBarManager?.statusBarFrame.height ?? 0.0) +
            (self.navigationController?.navigationBar.frame.height ?? 0.0)
    }
}

objective - c 当keyWindow等于nil时谁有问题。 把上面的代码放在viewDidAppear中(不是viewDidLoad中)

这里的其他答案对我都没用，但这个对我有用。

var topSafeAreaHeight: CGFloat = 0
var bottomSafeAreaHeight: CGFloat = 0

  if #available(iOS 11.0, *) {
    let window = UIApplication.shared.windows[0]
    let safeFrame = window.safeAreaLayoutGuide.layoutFrame
    topSafeAreaHeight = safeFrame.minY
    bottomSafeAreaHeight = window.frame.maxY - safeFrame.maxY
  }

UIWindow *window = [[[UIApplication sharedApplication] delegate] window]; 
CGFloat fBottomPadding = window.safeAreaInsets.bottom;

Swift 5, Xcode 11.4

`UIApplication.shared.keyWindow` 

它将给出弃用警告。" keyWindow "在iOS 13.0中已弃用:不应该用于支持多场景的应用程序，因为它会在所有连接的场景中返回一个键窗口。我用这种方法。

extension UIView {

    var safeAreaBottom: CGFloat {
         if #available(iOS 11, *) {
            if let window = UIApplication.shared.keyWindowInConnectedScenes {
                return window.safeAreaInsets.bottom
            }
         }
         return 0
    }

    var safeAreaTop: CGFloat {
         if #available(iOS 11, *) {
            if let window = UIApplication.shared.keyWindowInConnectedScenes {
                return window.safeAreaInsets.top
            }
         }
         return 0
    }
}

extension UIApplication {
    var keyWindowInConnectedScenes: UIWindow? {
        return windows.first(where: { $0.isKeyWindow })
    }
}

extension UIViewController {
    var topbarHeight: CGFloat {
        return
            (view.window?.safeAreaInsets.top ?? 0) +
            (view.window?.windowScene?.statusBarManager?.statusBarFrame.height ?? 0.0) +
            (self.navigationController?.navigationBar.frame.height ?? 0.0)
    }
}