#nscoding

How to: Why NSUserDefaults failed to save NSMutableDictionary in iPhone SDK?

Why NSUserDefaults failed to save NSMutableDictionary in iPhone SDK?

I’d like to save an NSMutableDictionary object in NSUserDefaults. The key type in NSMutableDictionary is NSString, the value type is NSArray, which contains a list of object which implements NSCoding. Per document, NSString and NSArray both are conform to NSCoding.

I am getting this error:

[NSUserDefaults setObject: forKey:]:…

When we create a child mutable dictionary, which is an exact replica of another parent mutable dictionary, often there would be a situation, where you change value for one key of the child dictionary and the value for same key would be changed for the parent dictionary too.

And, vice-versa. Changing values for parent dictionary would reflect for the images of child dictionary.

For this, what we would have to do is, Deep Copy. And deep copy, in true sense, for NSMutableDictionary or NSMutableArray would be done very easily with NSCoding (serialization) protocol.

  - (id) deepCopy:(id)mutableObjectToBeCopied

{

    NSData *buffer = [NSKeyedArchiver archivedDataWithRootObject: mutableObjectToBeCopied];

    return [NSKeyedUnarchiver unarchiveObjectWithData: buffer];

Forget all the hard work swizzling stuff and making things conform to NSCoding, it’s not always easy anyway. You can simply call -initWithRootController: twice. That’s the spirit.

UIViewController *emptyVC = [[[UIViewController alloc] init] autorelease]; __block WANavigationController *navController = [[[WANavigationController alloc] initWithRootViewController:emptyVC] autorelease]; navController = [[((^ { NSKeyedUnarchiver *unarchiver = [[[NSKeyedUnarchiver alloc] initForReadingWithData:[NSKeyedArchiver archivedDataWithRootObject:navController]] autorelease]; [unarchiver setClass:[WANavigationBar class] forClassName:@"UINavigationBar"]; [unarchiver setClass:[UIViewController class] forClassName:NSStringFromClass([navController.topViewController class])]; return unarchiver; })()) decodeObjectForKey:@"root"] initWithRootViewController:navController.topViewController];