//獲取當前屏幕顯示的ViewController
- (UIViewController *)getCurrentVC
{
    UIViewController *result = nil;
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    if (window.windowLevel != UIWindowLevelNormal)
    {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow * tempWindow in windows)
        {
            if (tempWindow.windowLevel == UIWindowLevelNormal)
            {
                window = tempWindow;
                break;
            }
        }
    }
    UIView *frontView = [[window subviews] objectAtIndex:0];
    id nextResponder = [frontView nextResponder];
    if ([nextResponder isKindOfClass:[UIViewController class]])
        result = nextResponder;
    else
        result = window.rootViewController;
    return result;
}