在项目开发中，我们经常会遇到Controller中添加多个ChildController。在我们ChildController中我们要实现页面跳转，就必须要获取当前的主Controller。
我们可以为UIApplication添加一个分类UIApplication+GYApplication.h

- (UIWindow *)mainWindow{
    return self.delegate.window;
}

- (UINavigationController *)visibleNavigationController{
    return [[self visibleViewController] navigationController];
}

- (UIViewController *)visibleViewController{
    UIViewController *rootviewcontroller = [self.mainWindow rootViewController];
    return [self getVisibleViewControllerFrom:rootviewcontroller];
} 

//逐层遍历，获取当前所在控制器
- (UIViewController *)getVisibleViewControllerFrom:(UIViewController *)vc{
    if ([vc isKindOfClass:[UINavigationController class]]) {
        return [self getVisibleViewControllerFrom:[((UINavigationController *) vc)visibleViewController]];
    }else if ([vc isKindOfClass:[UITabBarController class]]){
        return [self getVisibleViewControllerFrom:[((UITabBarController *) vc)selectedViewController]];
    }else{
        if (vc.presentedViewController) {
            return [self getVisibleViewControllerFrom:vc.presentedViewController];
        }else{
            return vc;
        }
    }
}

使用

UINavigationController *navi = [[UIApplication sharedApplication]visibleNavigationController];
[navi pushViewController:[[ViewController alloc]init] animated:YES];