通过按钮可Push ViewController，代理方式却失效的问题排查

• 故事板结构：NavigationController -> HomeScreenVC -> LogInVC（模态弹出）
• 需求：登录成功后，先dismiss LogInVC，再由HomeScreenVC Push MyAccountVC
• 异常现象：通过代理通知HomeScreenVC登录成功后，代理方法logInSucceded()中的Push操作无效；但按钮触发的Push完全正常，控制台能打印delegate123，说明代理配置无问题

相关代码 #

func logInSucceded() {
    print("delegate123")
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let viewController = storyboard.instantiateViewController(withIdentifier: "MyAccountViewController") as! MyAccountViewController
    navigationController?.pushViewController(viewController, animated: true)
}


@IBAction func loginbutton(_ sender: Any) {
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let viewController = storyboard.instantiateViewController(withIdentifier: "MyAccountViewController") as! MyAccountViewController
    navigationController?.pushViewController(viewController, animated: true)
}

解决思路 #

1. 调整dismiss与代理调用的顺序
   核心问题大概率是代理方法调用时，LogInVC还未完成dismiss操作，此时HomeScreenVC的navigationController处于状态不稳定的状态。需要确保先完成LogInVC的dismiss，再触发Push操作：

   // 在LogInVC的登录成功逻辑中修改
   dismiss(animated: true) { [weak self] in
       self?.delegate?.logInSucceded()
   }
   

2. 排查navigationController是否为nil
   按钮触发时正常，但代理方法调用时navigationController可能临时为nil。可以在代理方法中添加打印确认：

   func logInSucceded() {
       print("delegate123")
       print("navigationController状态: \(navigationController)") // 确认是否为nil
       let storyboard = UIStoryboard(name: "Main", bundle: nil)
       let viewController = storyboard.instantiateViewController(withIdentifier: "MyAccountViewController") as! MyAccountViewController
       navigationController?.pushViewController(viewController, animated: true)
   }
   

   如果确实为nil，可尝试直接获取根导航控制器来执行Push：

   guard let rootNav = UIApplication.shared.windows.first?.rootViewController as? UINavigationController else { return }
   rootNav.pushViewController(viewController, animated: true)
   

3. 确认HomeScreenVC是否在导航栈顶层
   检查代理方法调用时，HomeScreenVC是否还是navigationController的顶层视图控制器。如果有其他页面被Push过，Push操作会指向错误的导航栈。可添加打印排查：

   func logInSucceded() {
       print("delegate123")
       print("当前导航栈视图控制器: \(navigationController?.viewControllers ?? [])")
       // 后续Push代码
   }
   

内容的提问来源于stack exchange，提问作者Norbinette