iPhone: preserve NSUserDefaults values when application is killed - iphone

Question

I am trying to implement "Add to Favorites" functionality using NSUserDefaults. So far I have written following code.
- (void)favouriteButtonClicked:(id)sender
{
favselected = !favselected; // favselected is BOOL property
MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
NSString* viewname = #"custom";
if(favselected) {
[favButton setBackgroundImage:[UIImage imageNamed:#"selected.png"] forState:UIControlStateNormal];
[appDelegate addTOFavourites:self.ViewID viewType:self.ViewType];
} else {
[favButton setBackgroundImage:[UIImage imageNamed:#"unselected.png"] forState:UIControlStateNormal];
[appDelegate removeFromFavourites:self.ViewID viewType:self.ViewType];
}
}
It is working fine as long as my application is running but when I killed my application, I am losing all my stored values so when next time view loaded, in viewload isAddedToFavorites method returns false. Is there anyway to preserve my values? Am I missing something?
if([appDelegate isAddedToFavorites:self.ViewID]) {
[favButton setBackgroundImage:[UIImage imageNamed:#"selected.png"] forState:UIControlStateNormal];
favselected = YES;
} else {
[favButton setBackgroundImage:[UIImage imageNamed:#"unselected.png"] forState:UIControlStateNormal];
favselected = NO;
}
Edit:
I tried using NSMutableDictionary as I have to add multiple key-values but following method always display Count=0 even after adding object to dictionary. Any help would be really appreciated. Thank you.
-(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 {
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *dict = [[standardUserDefaults objectForKey:kFavouriteItemsKey] mutableCopy];
if(standardUserDefaults) {
if(![dict objectForKey:viewID])
[dict setObject:viewType forKey:viewID]; // It is coming here but still count zero!
NSLog(#"count = %d", [dict count]);
[standardUserDefaults setObject:dict forKey:kFavouriteItemsKey]; // Always dict remains null with 0 objects in it
[standardUserDefaults synchronize];
[dict release];
}
}
-(void)removeFromFavourites:(NSString*)viewID viewType:(NSString*)viewType {
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *dict = [[standardUserDefaults objectForKey:kFavouriteItemsKey] mutableCopy];
if(standardUserDefaults) {
if ([dict objectForKey:viewID])
[dict removeObjectForKey:viewID];
[standardUserDefaults setObject:dict forKey:kFavouriteItemsKey];
[standardUserDefaults synchronize];
[dict release];
}
}
Thanks.

Answer 1

NSUserDefaults is actually used to store values permanently, in fact if you create any Settings for your program they will be saved as NSUserDefaults.
I think the problem is that you are not saving it with the same key you are retrieving. Try saving like this:
//To save
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:appDefaults forKey:kFavouriteItemsKey];
[[NSUserDefaults standardUserDefaults] synchronize];
//To retrieve
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *favourites = [[standardUserDefaults objectForKey:kFavouriteItemsKey] mutableCopy];
For the dictionary try:
NSDictionary *myDictionary= [[NSUserDefaults standardUserDefaults] objectForKey:kFavouriteItemsKey];
// Create a mutable dictionary to replace the old immutable dictionary
NSMutableDictionary *myMutableDictionary= [NSMutableDictionary dictionaryWithCapacity:[myDictionary count]+1];
// transfer the old dictionary into the new dictionary
[myMutableDictionaryaddEntriesFromDictionary:myDictionary];
// Now add the data
[myMutableDictionary setObject:myObject forKey:myKey];