如果它是根，则可以执行此操作

You can do this if it's the root

if let vc = self.window?.rootViewController as? ViewController {
    vc.result.text = u
}

对于完整的解决方案，您应该使用获得最高的UIViewController 来获得最高的vc ，然后像上面一样投射

For a complete solution you should get the top most vc with Get top most UIViewController then cast it like above