iOS获取最顶层的ViewController

业务上，尤其是SDK的工程中，有时候需要在集中的地方获取当前显示的ViewController，便于present/dismiss或者push/pop的操作，又不会跟特定的业务ViewController产生依赖，可以用如下的方式，获取顶层的ViewController

//获取当前屏幕显示的viewcontroller
- (UIViewController *)getCurrentVC
{
    UIViewController *rootViewController = [self getViewControllerWindow].rootViewController;
    UIViewController *currentVC = [self getCurrentVCFrom:rootViewController];
    return currentVC;
}

//获取RootViewController所在的window
- (UIWindow*)getViewControllerWindow{
    UIWindow *window = [UIApplication sharedApplication].delegate.window;
    if (window.windowLevel != UIWindowLevelNormal) {
        NSArray *windows = [UIApplication sharedApplication].windows;
        for (UIWindow *target in windows) {
            if (target.windowLevel == UIWindowLevelNormal) {
                window = target;
                break;
            }
        }
    }
    return window;
}

- (UIViewController *)getCurrentVCFrom:(UIViewController *)rootVC
{
    UIViewController *currentVC;
    
    if ([rootVC presentedViewController]) {
        // 视图是被presented出来的
        while ([rootVC presentedViewController]) {
            rootVC = [rootVC presentedViewController];
        }
    }
    
    if ([rootVC isKindOfClass:[UITabBarController class]]) {
        // 根视图为UITabBarController
        currentVC = [self getCurrentVCFrom:[(UITabBarController *)rootVC selectedViewController]];
    } else if ([rootVC isKindOfClass:[UINavigationController class]]){
        // 根视图为UINavigationController
        currentVC = [self getCurrentVCFrom:[(UINavigationController *)rootVC visibleViewController]];
    } else {
        // 根视图为非导航类
        currentVC = rootVC;
        
    }
    
    return currentVC;
}