我有一个在应用程序启动时加载的类 MasterViewController。在 viewDidLoad() 中，它检查用户是否登录，并根据结果显示一个或另一个 View Controller 。如果您没有登录然后继续登录，应用程序会加载一个新的 MasterViewController。我的目标是基本上用一个新实例替换现有的 MasterViewController，以便它再次执行 viewDidLoad 中的检查。我尝试了以下方法，它们都有效:

// changing the root view controller
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

appDelegate.window = UIWindow(frame: UIScreen.mainScreen().bounds)
appDelegate.window!.rootViewController = MasterViewController()
appDelegate.window!.makeKeyAndVisible()

// using presentViewControllerAnimated
someViewController.presentViewControllerAnimated(MasterViewController(), animated: true, completion: nil)

...但是虽然 presentViewControllerAnimated 有一个很好的动画，但改变 root 却没有。更重要的是，更改 Root View Controller 不会破坏现有的 View Controller (至少永远不会调用 deinit ..)，显然 presentViewControllerAnimated 也不会这样做，所以在这两种情况下我都有这个 View Controller 漂浮在我不再想要的地方。

我可以想象这样一种场景，用户反复注销并重新登录，突然间我有 10 个 MasterViewController 一个叠一个。有什么方法可以完全清除 View Controller ？或者这完全没有必要？

编辑

刚记起 presentViewControllerAnimated 是用于模态呈现 vc，所以这绝对不是我想要的。不过，用类似的动画更改 Root View Controller 会很好。我看到的所有更改 root vc 的动画都非常不稳定。

最佳答案

以下 Stackoverflow 线程涉及您对内存中残留的旧 UIViewController 的担忧:

Stackoverflow: Changing root view controller of a iOS Window

serge-k的答案来自 UIWindow Class Reference :

var rootViewController: UIViewController?

The root view controller for the window.

The root view controller provides the content view of the window. Assigning a view controller to this property (either programmatically or using Interface Builder) installs the view controller’s view as the content view of the window. If the window has an existing view hierarchy, the old views are removed before the new ones are installed. The default value of this property is nil.

Resource Management in UIViewController UIViewController Programming Guide 的部分也包含关于此的注释:

The default behavior for a view controller is to load its view hierarchy when the view property is first accessed and thereafter keep it in memory until the view controller is disposed of. The memory used by a view to draw itself onscreen is potentially quite large. However, the system automatically releases these expensive resources when the view is not attached to a window. The remaining memory used by most views is small enough that it is not worth it for the system to automatically purge and recreate the view hierarchy.

You can explicitly release the view hierarchy if that additional memory is necessary for your app. Listing 4-3 overrides the didReceiveMemoryWarning method to accomplish this. First, is calls the superclass’s implementation to get any required default behavior. Then, it cleans up the view controller’s resources. Finally, it tests to see if the view controller’s view is not onscreen. If the view is associated with a window, then it cleans up any of the view controller’s strong references to the view and its subviews. If the views stored data that needs to be recreated, the implementation of this method should save that data before releasing any of the references to those views.

关于iOS - presentViewControllerAnimated 与 window.rootViewController，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30679428/