ios - 登录成功后如何呈现不同的ViewController

Question

我使用 Firebase 作为后端，并编写了登录部分。当我使用测试帐户登录时，调试器打印“已登录:”。但是，当我尝试转到主视图 Controller 时，出现错误“ fatal error :在展开可选值时意外发现 nil"代码在 self.presentviewcontroller 行中断。这里做错了什么？

 if email != "" && password != ""
    {
        FIREBASE_REF.authUser(email, password: password, withCompletionBlock: {(error, FAuthData) -> Void in

            if error == nil
            {
                NSUserDefaults.standardUserDefaults().setValue(FAuthData.uid, forKey: "uid")

                print("logged in")
                self.logoutButton.hidden = false

                let storyboard = UIStoryboard(name: "Main", bundle: nil)
                let secondViewController = storyboard.instantiateViewControllerWithIdentifier("ViewController") as! ViewController
                self.presentViewController(secondViewController, animated: true, completion: nil)

            }
            else{
                print("The user was not logged in")
            }

        })
    }
    else{
        let alert = UIAlertController(title: "ERROR", message: "Please Enter Email and Password", preferredStyle: .Alert)
        let action = UIAlertAction(title: "OK", style: .Default, handler: nil)
        alert.addAction(action)
        self.presentViewController(alert, animated: true, completion: nil)
    }

Answer 1

检查您的主 Storyboard是否将标识符 ViewController 设置为您的 ViewController。