SwiftUI iOS15中windows已弃用 如何改用UIWindowScene语法获取安全边距

错误原因：UIApplication.shared.windows 从iOS15开始被废弃，UIWindowScene.windows 是实例属性，不能直接通过类名调用，需要先获取当前App活跃的窗口场景实例才能调用。

方案1：最小改动适配UIKit新API #

仅调整窗口获取逻辑，兼容iOS13及以上版本：

struct StackOverflow: View {
    var body: some View {
        Text("Hello, World!")
            .padding(.bottom, getSafeAreaBottom() ?? 15)
    }
    
    private func getSafeAreaBottom() -> CGFloat? {
        // 筛选当前前台活跃的窗口场景
        let activeScene = UIApplication.shared.connectedScenes
            .first { $0.activationState == .foregroundActive } as? UIWindowScene
        return activeScene?.windows.first?.safeAreaInsets.bottom
    }
}

方案2：纯SwiftUI原生实现（更推荐） #

直接使用SwiftUI提供的安全边距环境变量，无需依赖UIKit，性能更优：

struct StackOverflow: View {
    // 读取系统自带的安全边距环境变量
    @Environment(\.safeAreaInsets) private var safeAreaInsets
    
    var body: some View {
        Text("Hello, World!")
            .padding(.bottom, safeAreaInsets.bottom == 0 ? 15 : safeAreaInsets.bottom)
    }
}

如果需要兼容iOS14及更早版本，可以补充以下扩展实现低版本兼容：

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

private struct SafeAreaInsetsKey: EnvironmentKey {
    static var defaultValue: EdgeInsets {
        let activeScene = UIApplication.shared.connectedScenes
            .first { $0.activationState == .foregroundActive } as? UIWindowScene
        return activeScene?.windows.first?.safeAreaInsets.swiftUiInsets ?? EdgeInsets()
    }
}

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

内容的提问来源于stack exchange，提问作者SwiftUIRookie