iOS更换默认的启动ViewController的几种方法总结

新建一个iOS工程，系统会自动创建ViewController，并在Main.storyboard中引用它作为主页面。这是一个基本的ViewController，如果要改成带导航栏的UINavigationController或者其他的，就得更换。网上搜了一下，资料很乱，改的地方很多，而且有的生效，有的不生效。

总结整理了一下有四种方法。

方法一：修改Main.Storyboard

如图，选中Main.Storyboard - My View Controller，选择右边的蓝色标签，把Class类名改成你的类即可，当然这个类只能是ViewController类型的。

方法二：修改Main.Storyboard，更换其他类型的Controller

以UINavigationController为例，选中Main.Storyboard，点右上角加号，在如下弹窗中输入UINavigationController，选择它添加到Storyboard中。

这时会出现三个Controller，一个系统创建的ViewController，还有就是刚添加的UINavigationController和它的rootViewController。把ViewController最左边的箭头也就是Entry Point拖动到UINavigationController左边，再点击ViewController按删除键删除。最后跟方法一一样，点击rootViewController，把Class类名改成你的类。

方法三：修改SceneDelegate

大部分网上教程都是修改AppDelegate，但是Xcode11以后会自动创建SceneDelegate文件，这时修改AppDelegate是无效的。需要修改SceneDelegate，在SceneDelegate的willConnectTo方法中设置window的rootViewController。

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
        guard let _ = (scene as? UIWindowScene) else { return }
        
        let vc = MyViewController()
        let nc = UINavigationController(rootViewController: vc)
        window?.rootViewController = nc
    }

方法四：修改AppDelegate，删除SceneDelegate

先删除SceneDelegate，全局搜索SceneDelegate，把Info文件中的Application Scene Manifest节点删掉

并且把AppDelegate中和Scene相关的两个方法：configurationForConnecting和didDiscardSceneSessions删掉。这样SceneDelegate就不起作用了，可以直接删除。

class AppDelegate: UIResponder, UIApplicationDelegate {

    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    }


}

最后在AppDelegate中的didFinishLaunchingWithOptions方法中设置window和rootViewController就可以生效了。

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        
        let window = UIWindow(frame: UIScreen.main.bounds)
        let vc = ViewController()
        let nc = UINavigationController(rootViewController: vc)
        window.rootViewController = nc
        self.window = window
        window.makeKeyAndVisible()
        
        return true
    }

}