NSCache-not always cleaned? - ios

Question

I have NSCache in which i am loading from and to- images to be displayed in collection view .
When i have to reload data to the collection view, i must clean the cache, because otherwise the collection view will find old data in there and reload it instead of the new data.
So before i reload the collection i clean my cache :
[self.myCache removeAllObjects];
Which sometimes, is not working, and i still see the old images in the collection view .
Is there another way to go all over its values and clean them ? Why is it not being cleared ?
Here is how i load and get images from and to :
-(UIImage*) imageForIndexPathRow:(NSNumber *) number
{
return [self.myCache objectForKey:[NSString stringWithFormat:#"cache:%d",[number intValue]] ];
}
-(void) setImage:(UIImage*) image forIndexPathRow:(NSNumber *) number
{
if(image)
[self.myCache setObject:image forKey:[NSString stringWithFormat:#"cache:%d",[number intValue]] ];
}
EDIT:
This is how i check the cache before load image to cell(in another thread) :
UIImage *imageToSet=nil;
UIImage *cacheImg=[self imageForIndexPathRow:[NSNumber numberWithLong:cell.tag]];
if(cacheImg==nil)
{
UIImage *image=[UIImage imageWithData:data scale:1];
imageToSet=image;
//save to cache
[self setImage:image forIndexPathRow:[NSNumber numberWithLong:cell.tag]];
}
else
imageToSet=cacheImg;

Answer 1

The problem comes from CollectionView cell reusing
you need to implement the else case, like this
- (UIImage *)imageForIndexPathRow:(NSNumber *) number
{
UIImage *cachedImage = [self.myCache objectForKey:[NSString stringWithFormat:#"cache:%d", [number intValue]]];
if (cachedImage) {
return cachedImage;
}
// Otherwise load it from web
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:#"http://...yourImageURL"]];
UIImage *loadedImage = [UIImage imageWithData:imageData];
// Cache it back
[self.myCache setObject:loadedImage forKey:[NSString stringWithFormat:#"cache:%d", [number intValue]]];
return loadedImage;
}
and the cellForRow should look like this (my example is on UITableView, but you can port it to CollectionView)
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:#"YourCellId"];
cell.image = nil;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
UIImage *image = [self imageForIndexPathRow:#(indexPath.row)];
dispatch_async(dispatch_get_main_queue(), ^{
cell.image = image;
});
});
return cell;
}