Swift 在将数据从一个ViewController传递到下一个ViewController时遇到问题

几个月来我一直在学习swift，有一件事我一直搞砸了，那就是在ViewController之间传递数据。当我从

prepareForSegue

方法中输入前瞻变量的路径时，该值是完整的。但当新的ViewController实际出现时，我检查了它的值，此时它为零。如果有人能给我指出正确的方向，我将非常感激

class LoginViewController: UIViewController {

var user_ID:String = ""

//this below is within another method activated by button
  Auth.auth().signIn(withEmail: email, password: password) { (result, error) in
        if error != nil {
            print ("there was an error signing in")
            print (error!.localizedDescription)
            return
        }
        else {
            //go to home screen
            let userUID = result?.user.uid
            print (userUID)
            self.user_ID = userUID
            
            self.performSegue(withIdentifier: "MainSegue", sender: self)
        }
    

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    
    //this is the destination VC
    let viewController = segue.destination as! ViewController
        
    viewController.user_ID = self.user_ID
    
    //NOTE: if I break here and PO viewConroller.user_ID the value is intact

    let homeViewController = (self.storyboard?.instantiateViewController(withIdentifier: "MainVC"))! as! ViewController
             
                //let mainViewController = ViewController()
                //mainViewController.user_ID = userUID
                                  
    self.present(homeViewController, animated: true, completion: nil)
   
}








class ViewController: UIViewController {

var persons = [Person]()
let db = Firestore.firestore()

 var user_ID:String = ""

 //NOTE: WHEN `viewdidload` runs value of user_ID is nil

---

Phillip在上述评论中提供了解决方案。当前的ViewController就是问题所在。赛格已经做到了。谢谢你

self.user_ID，您在哪里初始化用户_ID？我已在LoginViewController（原始VC）和ViewController类（目标）中声明：var user_ID:String=“”，不创建和显示第二个视图控制器。让segue在

目的地中放置一个。您正在一个实例中设置数据，然后呈现另一个实例。谢谢Phillip！！！你说得很对，这很有效。你是个天才！！！