以导航控制器为初始视图控制器的依赖注入问题解决

我查遍了状态共享相关的依赖注入教程，都没提到导航控制器作为初始视图控制器的场景。我尝试在AppDelegate里注入BidDetailsController，但因为HomeViewController被嵌入在导航控制器中，注入没有成功，导致使用BidDetailsController内的值时一直出现nil错误。

我原来的AppDelegate代码：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // 导航栏样式配置
    let navigationBarAppearance = UINavigationBarAppearance()
    navigationBarAppearance.configureWithTransparentBackground()
    navigationBarAppearance.titleTextAttributes = [.foregroundColor: UIColor.white]
    navigationBarAppearance.backgroundColor = #colorLiteral(red: 0.9686274529, green: 0.78039217, blue: 0.3450980484, alpha: 1)
    UINavigationBar.appearance().tintColor = .white
    
    UINavigationBar.appearance().standardAppearance = navigationBarAppearance
    UINavigationBar.appearance().compactAppearance = navigationBarAppearance
    UINavigationBar.appearance().scrollEdgeAppearance = navigationBarAppearance
    
    // 尝试依赖注入，但无效
    let homeViewController = HomeViewController()
    homeViewController.bidDetailsController = BidDetailsController()
    
    return true
}

相关视图控制器代码：

class HomeViewController: UIViewController {
    
    var bidDetailsController: BidDetailsController!

    override func viewDidLoad() {
        super.viewDidLoad()
        title = "HOME"
        // 这里重新实例化会覆盖注入的对象
        bidDetailsController = BidDetailsController()
    }
    
    @IBAction func menuBtnTapped(_ sender: Any) {
        print("Show Menu")
    }
    
    @IBAction func newBidBtnTapped(_ sender: Any) {
        performSegue(withIdentifier: "homeToInfoSegue", sender: self)
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let infoViewController = segue.destination as? InfoViewController {
            infoViewController.bidDetailsController = bidDetailsController
        }
    }
    
}

class BidDetailsController {
    var exampleVariableOne = String()
    var exampleVariableTwo = Bool()
}

问题出在两个核心点：

• 你在AppDelegate里新建了一个HomeViewController实例，但实际运行时用的是Storyboard中导航控制器自带的HomeViewController实例，两者不是同一个对象，所以注入完全无效。
• HomeViewController的viewDidLoad里重新实例化了BidDetailsController，就算之前注入成功，也会被覆盖成新的实例。

按照以下步骤修改即可解决：

1. 修正AppDelegate中的注入逻辑 #

从Storyboard中获取实际运行的初始导航控制器，再拿到它的根视图控制器（也就是你的HomeViewController），然后注入共享的BidDetailsController实例：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // 保留原有导航栏样式配置代码
    let navigationBarAppearance = UINavigationBarAppearance()
    navigationBarAppearance.configureWithTransparentBackground()
    navigationBarAppearance.titleTextAttributes = [.foregroundColor: UIColor.white]
    navigationBarAppearance.backgroundColor = #colorLiteral(red: 0.9686274529, green: 0.78039217, blue: 0.3450980484, alpha: 1)
    UINavigationBar.appearance().tintColor = .white
    
    UINavigationBar.appearance().standardAppearance = navigationBarAppearance
    UINavigationBar.appearance().compactAppearance = navigationBarAppearance
    UINavigationBar.appearance().scrollEdgeAppearance = navigationBarAppearance
    
    // 正确的依赖注入逻辑
    guard let window = UIApplication.shared.windows.first,
          let navController = window.rootViewController as? UINavigationController,
          let homeVC = navController.rootViewController as? HomeViewController else {
        return true
    }
    // 创建全局共享的BidDetailsController实例
    let sharedBidController = BidDetailsController()
    homeVC.bidDetailsController = sharedBidController
    
    return true
}

2. 移除HomeViewController中的重复实例化代码 #

删除viewDidLoad里重新创建BidDetailsController的代码，避免覆盖注入的共享实例：

class HomeViewController: UIViewController {
    
    var bidDetailsController: BidDetailsController!

    override func viewDidLoad() {
        super.viewDidLoad()
        title = "HOME"
        // 移除这行代码：bidDetailsController = BidDetailsController()
    }
    
    // 其余方法保持不变
}

3. 验证状态共享 #

现在HomeViewController里的bidDetailsController是从AppDelegate注入的全局共享实例，通过prepare(for:sender:)传递给InfoViewController后，两个页面操作的是同一个BidDetailsController对象，状态会自动保持同步。

内容的提问来源于stack exchange，提问作者Christian W