iPhone: Not able to store NSMutableDictionary to NSUserDefaults

Question

I am trying to implemen "Add to Favorites" functionality using NSMutableDictionary as I have to add multiple key-values. The following addToFavourites method always display Count=0 even after adding object to dictionary. I read this and getting nsdefaults into mutabledictionary(instead of mutable array) and setting resulted dictionary back to nsdefaults but not sure what's the problem. Any help would be really appreciated. Thank you.

Edited: From this I came to know that I have to move data around mutable and immutable dictionary and then it worked fine! but still not able to synchronize modified NSMutableDictionary to NSUserDefaults.

-(BOOL)isAddedToFavorites:(NSString*)viewID {
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *favourites = [[standardUserDefaults objectForKey:kFavouriteItemsKey] mutableCopy];

if(favourites && [[favourites objectForKey:kFavouriteItemsKey] objectForKey:viewID])
return YES;

return NO;
}

-(void)addToFavourites:(NSString*)viewID viewType:(NSString*)viewType {
NSMutableDictionary *myMutableDictionary= [NSMutableDictionary dictionaryWithCapacity:[myDictionary count]+1];
[myMutableDictionary addEntriesFromDictionary:myDictionary];
[myMutableDictionary setObject:myObject forKey:myKey];


// Modified dictionary is not getting synced
[[NSUserDefaults standardUserDefaults]  setObject:myMutableDictionary  forKey:kFavouriteItemsKey];
[[NSUserDefaults standardUserDefaults]  synchronize];
}

Tried encoding dictionary data to NSData and it worked now after minor but serious corrections!

-(BOOL)isAddedToFavorites:(NSString*)viewID {

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:kFavouriteItemsKey];
NSDictionary *favourites = [NSKeyedUnarchiver unarchiveObjectWithData:data]; 

if(favourites && [favourites objectForKey:viewID])
    return YES;

return NO;
}

-(void)addToFavourites:(NSString*)viewID viewType:(NSString*)viewType {

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:kFavouriteItemsKey];
NSDictionary *myDictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data]; 

NSMutableDictionary *myMutableDictionary= [NSMutableDictionary dictionaryWithCapacity:[myDictionary count]+1];
[myMutableDictionary addEntriesFromDictionary:myDictionary];
[myMutableDictionary setObject:viewType forKey:viewID];


NSData *newdata = [NSKeyedArchiver archivedDataWithRootObject:myMutableDictionary];
[[NSUserDefaults standardUserDefaults] setObject:newdata forKey:kFavouriteItemsKey];
[[NSUserDefaults standardUserDefaults] synchronize];
}

Thanks.

Answer 1

You will need to implement this for the elements in your dictionary:

The element in the dictionary implements

@interface CommentItem : NSObject<NSCoding> {
    NSString *value;
}

Then in the implementation of CommentItem, provides two methods:

-(void)encodeWithCoder:(NSCoder *)encoder
{
    [encoder encodeObject:value forKey:@"Value"];
}

-(id)initWithCoder:(NSCoder *)decoder
{
    self.value = [decoder decodeObjectForKey:@"Value"];
    return self;
}

As suggested on the link @Irene provided.