Opening app from last opened UIViewController - iphone

Question

I need my app to remember which was the last UIViewController opened so when the app is loaded out of memory, I substitute a rootViewController property in the AppDelegate with one saved in NSUserDefaults:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
UIWindow *window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.window = window;
frontViewController = [[SGLoginScreenViewController alloc] init];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:frontViewController];
self.window.rootViewController = navController;
[self.window makeKeyAndVisible];
return YES;
}
What I want to do is to put some code in the ViewDidLoad method of each ViewController and remember its name in NSUserDefaults to later use it in didFinishLaunchingWithOptions, something like this:
[[NSUserDefaults standardUserDefaults] setObject:self forKey:#"currentViewController"];
[[NSUserDefaults standardUserDefaults] synchronize];
The problem is, however, that XCode is giving me this warning:
*** -[NSUserDefaults setObject:forKey:]: Attempt to insert non-property value '<SGMainScreenFirstTimeViewController: 0x8e1fea0>' of class 'SGMainScreenFirstTimeViewController'. Note that dictionaries and arrays in property lists must also contain only property values.
Any ideas on how to implement this whole thing right? Thanks in advance

Answer 1

You can only save in user defaults objects that can conform to the Key-Value coding (NSString, NSnumber, etc). Converting class to string and recreating class knowing class name would be the way to go for what you wish to achieve.
This would be a good approach for saving in NSUserDefaults
[[NSUserDefaults standardUserDefaults] setObject:NSStringFromClass([self class]); forKey:#"currentViewController"];
[[NSUserDefaults standardUserDefaults] synchronize];
And for loading back you recreate the class based on the saved string, as below:
NSString *savedClassName = [[NSUserDefaults standardUserDefaults] objectForKey:#"currentViewController"];
UIViewController *controller = [(UIViewController *)NSClassFromString(savedClassName) alloc] init];

Answer 2

NSUSerDefaults is basically to store default values... not big objects ( list of items that can be saved includes (NSString,NSData,NSDictionary,NSArray,NSNumber) ..keep that in mind next time.
better way to do the functionality.
[[NSUserDefaults standardUserDefaults] setObject:#"Second View" forKey:#"currentViewController"];
[[NSUserDefaults standardUserDefaults] synchronize];
and then on app Load
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
if ([[[NSUserDefaults standardUserDefaults] objectForKey:#"currentViewController"] isEqualToString:#"Second View"])
{
//your code/logic

Answer 3

According to the documentation:
The value parameter can be only property list objects: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. For NSArray and NSDictionary objects, their contents must be property list objects.
So you can save name of your view controller and restore it on start, knowing its name

Answer 4

First thing is you can't save mutable values in NSUserDefaults. just check the psudocode following :
[[NSUserDefaults standardUserDefaults] setObject:#"nibnameofcurrentViewController" forKey:#"currentViewController"];
[[NSUserDefaults standardUserDefaults] synchronize];
when your app launch again then do following:
UIViewController *controller=[[UIViewController alloc]initWithNibName:[[NSUserDefault standerdDefault]objectForkey:#"currentViewController"] bundle:nil];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:frontViewController];
self.window.rootViewController = navController;