How to "restart" iOS app / re-instanciate inital view controller from UIApplicationDelegate instance?

Question

My first iOS app (utility) release is nearing completion but one issue remains: The app runs an automated sequence. On most other platforms, the sequence would complete/fail/cancel then would be followed by clean up and exit(x).

I realise that my iOSapp should not exit() so it returns to the UIApplicationDelegate where it performs the clean up; setting all of the controllers to nil (using ARC), leaving only the appDelegate instance standing. The app then should re-instanciate the initial view controller, effectively starting the app again.

What call from the UIApplicationDelegate does this? I expect that it should be the same as that called by iOS upon initial storyboarded app startup.

Answer 1

You should define a (public) method in your application delegate class and call it when necessary. In that method, you should re-instantiate your initial view controller and set it as root view controller of your UIWindow instance (you should have an ivar with it).

AppDelegate.h:

- (void) resetApp;

AppDelegate.m:

- (void) resetApp {
    TopViewController* controller = [[TopViewController alloc] init];

    _window.rootViewController = controller;
}

---

Edit: If you are usign storyboards, this code works:

AppDelegate.swift (because it's 2017):

func resetApp() {
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    guard let newRoot = storyboard.instantiateInitialViewController() else {
        return // This shouldn't happen
    }
    self.window?.rootViewController = newRoot
}

(This assumes your app's initial storyboard -the one specified in Info.plist- is called "Main.storyboard")

If your app is designed in such a way that long or asynchronous operations might be in progress when this reset happens, additional considerations should be taken to deal with them. For starters, all view controllers that aren't implemented as singletons or retained by such long-lived objects will likely be deallocated.