//获取当前屏幕显示的viewcontroller 
- (UIViewController *)getCurrentVC {
    
    UIViewController *result = nil;
    
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    
    //寻找当前显示的window    （若项目只有一个window  可省略）
    if (window.windowLevel != UIWindowLevelNormal)  {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow * tmpWin in windows)  {
            
            if (tmpWin.windowLevel == UIWindowLevelNormal)  {
                
                window = tmpWin;
                break;
            }
        }
    }
    
    UIViewController *root = window.rootViewController;
    
    while (root) {
        if ([root isKindOfClass:[UITabBarController class]]) {
            UITabBarController *tab = (UITabBarController *)root;
            root = tab.selectedViewController;
        }
//        else if ([root isKindOfClass:[GKNavigationController class]]){
//            root = ((GKNavigationController *)root).gk_topViewController;
//        }
        else if([root isKindOfClass:[UINavigationController class]]) {
            root = root.childViewControllers.lastObject;
        }
        else if (root.presentedViewController){
            root = root.presentedViewController;
        }
        else{
            result = root;
            root = nil;
        }
    }
    return result;
}