对于 SwiftUI：

Code

private struct SafeAreaInsetsKey: EnvironmentKey {
    static var defaultValue: EdgeInsets {
        UIApplication.shared.windows[0].safeAreaInsets.insets
    }
}

extension EnvironmentValues {
    
    var safeAreaInsets: EdgeInsets {
        self[SafeAreaInsetsKey.self]
    }
}

private extension UIEdgeInsets {
    
    var insets: EdgeInsets {
        EdgeInsets(top: top, leading: left, bottom: bottom, trailing: right)
    }
}

使用

struct MyView: View {
    
    @Environment(\.safeAreaInsets) private var safeAreaInsets
    
    var body: some View {
        Text("Ciao")
            .padding(safeAreaInsets)
    }
}

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 })
    }
}

safeAreaLayoutGuide 当视图在屏幕上可见时，该指南反映了未被导航栏、选项卡栏、工具栏和其他祖先视图覆盖的视图部分。(在tvOS中，安全区域反映未覆盖屏幕边框的区域。)如果视图当前没有安装在视图层次结构中，或者在屏幕上还不可见，布局指南边等于视图的边。

然后在截图中获得红色箭头的高度:

self.safeAreaLayoutGuide.layoutFrame.size.height

这里有一个基于其他答案的免费函数，当你的rootController从任何地方布局时，它都应该是可调用的。你可以把它当做一个独立的函数。

    func safeAreaInsets() -> UIEdgeInsets? {
    (UIApplication
        .shared
        .keyWindow?
        .rootViewController)
        .flatMap {
            if #available(iOS 11.0, *) {
                return $0.view.safeAreaInsets
            } else {
                return .init(
                    top: $0.topLayoutGuide.length,
                    left: .zero,
                    bottom: $0.bottomLayoutGuide.length,
                    right: .zero
                )
            }
        }
}

这里有一个简单的答案，可以找到所有iphone的安全区域高度

let window = UIApplication.shared.windows[0]

let SafeAreaHeight = window.safeAreaLayoutGuide.layoutFrame.size.height

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