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POCorrect way to create and restore UIViewControllers during state restoration?
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copied!<p>I'd like to do state restoration in my app that doesn't use story boards. I'm seeing my primary app ViewController instantiated twice during state restoration - how do you ensure that it's only created once?</p> <p>The way I understand the flow, <code>application:willFinishLaunchingWithOptions</code> and a<code>pplication:didFinishLaunchingWithOptions</code> would use a <code>commonInit</code> method which would setup the applications UIWindow and its rootViewController. In my case, the rootViewController is a UINavigationController with a class named 'MyMainViewController' serving as UINavigation's rootViewController.</p> <p>Along side this I'm also handling <code>willEncodeRestorableStateWithCoder</code> and <code>didDecodeRestorableStateWithCoder</code>, respectively. But it seems that by the time I get to my <code>didDecodeRestorableStateWithCoder</code>, I see two separate instances of MyMainViewController created.</p> <p>What's the way to ensure that only one UIViewController is created during restoration?</p> <p>Order of calls during restoration:</p> <ul> <li>Create new instance MyMainViewController (#1) via application:willFinishLaunchingWithOptions:</li> <li>MyMainViewController's viewControllerWithRestorationIdentifierPath:coder invoked and MainViewController is restored (#2)</li> <li>application:didDecodeRestorableStateWithCoder: is called and UINavigationController is decoded and assigned to self.window</li> </ul> <p>Here's what I'm doing in my AppDelegate:</p> <pre><code>NSString * const kRootViewControllerKey = @"RootViewControllerKey"; - (BOOL)application:(UIApplication *)application willFinishLaunchingWithOptions:(NSDictionary *)launchOptions { [self commonInitWithOptions:launchOptions]; return YES; } - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { [self commonInitWithOptions:launchOptions]; return YES; } - (void)commonInitWithOptions:(NSDictionary *)launchOptions { static dispatch_once_t predicate; dispatch_once(&predicate, ^ { // While this will be called only once during the lifetype of the app, when the process is killed // and restarted, I wind up with an instance of MyMainViewController created first from here // and then once again, during MyMainViewController's viewControllerWithRestorationIdentifierPath:coder // that's invoked later on. UIViewController *rootViewController = [MyMainViewController alloc] init]; UINavigationController *aNavController = [[UINavigationController alloc] initWithRootViewController:rootViewController]; aNavController.navigationBarHidden = YES; aNavController.restorationIdentifier = NSStringFromClass([aNavController class]); UIWindow *aWindow = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; aWindow.rootViewController = aNavController; aWindow.restorationIdentifier = NSStringFromClass([window class]); self.window = aWindow; }); } // Encode app delegate level state restoration data - (void)application:(UIApplication *)application willEncodeRestorableStateWithCoder:(NSCoder *)coder { [coder encodeObject:self.window.rootViewController forKey:kRootViewControllerKey]; } // Decode app delegate level state restoration data - (void)application:(UIApplication *)application didDecodeRestorableStateWithCoder:(NSCoder *)coder { // Find the preserved root view controller and restore with it UINavigationController *navControlller = [coder decodeObjectForKey:kRootViewControllerKey]; if (navControlller) { self.window.rootViewController = navControlller; } } </code></pre>

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