獲取當前頁面所在的controller

這是從IQKeyBoardManager裏面看到的兩個函數，覺得臥槽。太有用啦。跟大家分享一下：

//獲取最上層的控制器：window最上層的控制器：包含UINavigationController

- (UIViewController*)topMostController
{
    UIViewController *topController = [self rootViewController];
    
    //  Getting topMost ViewController
    while ([topController presentedViewController])    topController = [topController presentedViewController];
    
    //  Returning topMost ViewController
    return topController;
}

//當最上層的控制器是UINavigationController時。你需要通過該方法來獲取UINavigationController的子控制器棧的最上層的UIViewController
- (UIViewController*)currentViewController;
{
    UIViewController *currentViewController = [self topMostController];
    
    while ([currentViewController isKindOfClass:[UINavigationController class]] && [(UINavigationController*)currentViewController topViewController])
        currentViewController = [(UINavigationController*)currentViewController topViewController];
    
    return currentViewController;
}