获取程序最上层UIViewController

1.如何获取应用topviewcontroller?

static UIViewController *get_top_view_controller() {
    UIViewController *vc = UIApplication.sharedApplication.keyWindow.rootViewController;
    while (  [vc isKindOfClass:[UINavigationController class]] ||
             [vc isKindOfClass:[UITabBarController class]] ||
              vc.presentedViewController ) {
        if ( [vc isKindOfClass:[UINavigationController class]] )
            vc = [(UINavigationController *)vc topViewController];
        if ( [vc isKindOfClass:[UITabBarController class]] )
            vc = [(UITabBarController *)vc selectedViewController];
        if ( vc.presentedViewController )
            vc = vc.presentedViewController;
    }
    return vc;
}
//上面这个方法,如果要对外暴露成OC方法接口应该改成下面写法:

+( UIViewController *)get_top_view_controller() {
    UIViewController *vc = UIApplication.sharedApplication.keyWindow.rootViewController;
    while (  [vc isKindOfClass:[UINavigationController class]] ||
             [vc isKindOfClass:[UITabBarController class]] ||
              vc.presentedViewController ) {
        if ( [vc isKindOfClass:[UINavigationController class]] )
            vc = [(UINavigationController *)vc topViewController];
        if ( [vc isKindOfClass:[UITabBarController class]] )
            vc = [(UITabBarController *)vc selectedViewController];
        if ( vc.presentedViewController )
            vc = vc.presentedViewController;
    }
    return vc;
}

//思路: 
//1.获取应用当前rootViewController(根视图),注意:根视图是程序的最底层视图控制器层
//2.存在可能性: UINavigationController/UITabBarController/UIViewController
//3.只要当上面最后获得的VC.presentedViewController == nil
//才能说明当前的控制器是最顶层的