iOS学习—在View等页面实现控制器跳转等操作_获取navigationcontroller

 通过以下方法，直接通过[self getNavigationController]获取

iOS13之前：

 
/// 获取Nav
- (UINavigationController *)getNavigationController {
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    if ([window.rootViewController isKindOfClass:[UINavigationController class]]) {
        return (UINavigationController *)window.rootViewController;
    } else if ([window.rootViewController isKindOfClass:[UITabBarController class]]) {
        UIViewController *selectedVC = [((UITabBarController *)window.rootViewController)selectedViewController];
        if ([selectedVC isKindOfClass:[UINavigationController class]]) {
            return (UINavigationController *)selectedVC;
        }
    }
    return nil;
}

iOS13之后：

iOS13之后会提示‘keyWindow‘ is deprecated: first deprecated in iOS 13.0 - Should not be used for applications that 

由于iOS 13.0中已弃用“ keyWindow”：不应将其用于支持多个场景的应用程序，因为它会返回所有已连接场景的关键窗口。

我们将[UIApplication sharedApplication].keyWindow 改为 [[[UIApplication sharedApplication] windows] objectAtIndex:0]，具体如下：

- (UINavigationController *)getNavigationController {
    UIWindow *window = [[[UIApplication sharedApplication] windows] objectAtIndex:0];
    if ([window.rootViewController isKindOfClass:[UINavigationController class]]) {
        return (UINavigationController *)window.rootViewController;
    } else if ([window.rootViewController isKindOfClass:[UITabBarController class]]) {
        UIViewController *selectedVC = [((UITabBarController *)window.rootViewController)selectedViewController];
        if ([selectedVC isKindOfClass:[UINavigationController class]]) {
            return (UINavigationController *)selectedVC;
        }
    }
    return nil;
}