NSCache does not work - iphone

Question

I'm writing an app that needs store a few images in cache. I'm trying to do it with NSCache and the code seems to be well but don't save the images in cache. I have this code:
cache is global, declared in .h: NSCache *cache;
-(UIImage *)buscarEnCache:(UsersController *)auxiliarStruct{
UIImage *image;
[[cache alloc] init];
NSLog(#"cache: %i", [cache countLimit]);
if ([cache countLimit] > 0) { //if [cache countLimit]>0, it means that cache isn't empty and this is executed
if ([cache objectForKey:auxiliarStruct.thumb]){
image = [cache objectForKey:auxiliarStruct.thumb];
}else{ //IF isnt't cached, is saved
NSString *imageURLString = [NSString stringWithFormat:#"http://mydomain.com/%#",auxiliarStruct.thumb];
NSURL *imageURL = [NSURL URLWithString:imageURLString];
NSData * imageData = [NSData dataWithContentsOfURL:imageURL];
image = [UIImage imageWithData:imageData];
[cache setObject:image forKey:auxiliarStruct.thumb];
}
}else{ //This if is executed when cache is empty. IS ALWAYS EXECUTED BECAUSE FIRST IF DOESN'T WORKS CORRECTLY
NSString *imageURLString = [NSString stringWithFormat:#"http://mydomain.com/%#",auxiliarStruct.thumb];
NSURL *imageURL = [NSURL URLWithString:imageURLString];
NSData * imageData = [NSData dataWithContentsOfURL:imageURL];
image = [UIImage imageWithData:imageData];
[cache setObject:image forKey:auxiliarStruct.thumb];
}
return image;
}
This function is called in other function with this:
UIImage *image = [self buscarEnCache:auxiliarStruct];
This works because the image is displayed on screen but isn't saved in cache, the line that I think fails is:
[cache setObject:image forKey:auxiliarStruct.thumb]; //auxiliarStruct.thumb is the name of the image
Someone knows why cache doesn't work?? Thanks!!
ps: sorry for my english, I know is bad

Answer 1

Every time the method buscarEnCache: is called an new cache object is created with the line:
[[cache alloc] init];
Thus the old cache just leaked and is not available any more.
place the cache = [[NSCache alloc] init]; in the init method of the class.
There is no need to check for the countLimit.
-(UIImage *)buscarEnCache:(UsersController *)auxiliarStruct{
UIImage *image = [cache objectForKey:auxiliarStruct.thumb];
if (!image) {
NSString *imageURLString = [NSString stringWithFormat:#"http://mydomain.com/%#",auxiliarStruct.thumb];
NSURL *imageURL = [NSURL URLWithString:imageURLString];
NSData * imageData = [NSData dataWithContentsOfURL:imageURL];
image = [UIImage imageWithData:imageData];
[cache setObject:image forKey:auxiliarStruct.thumb];
}
return image;
}
You might want to place the fetch of the image in a method that runs in an other thread and return some kind of placeholder image.

Answer 2

As well as the answer provided by #rckoenes, you aren't allocating the cache instance correctly anyway; it should be:
cache = [[NSCache alloc] init];
Which should be moved into your init method.