How to remove a specific image from NSCache? - ios

Question

I have a collection view which has 12 images I retrieve from a network call. I use NSCache to cache them. I want to know how I can delete a specific image from there? I have provided some code below to show how I cached the images. Thanks!
override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("imageReuseCell", forIndexPath: indexPath) as! ImageCollectionViewCell
let image = hingeImagesArray[indexPath.row]
//Start animating activity indicator
cell.actitivityIndicator.startAnimating()
if let imageURL = image.imageUrl {
if let url = NSURL(string: imageURL) {
//Check for cached images and if found set them to cells - works if images go off screen
if let myImage = HomepageCollectionViewController.imageCache.objectForKey(image.imageUrl!) as? UIImage {
cell.collectionViewImage.image = myImage
}else {
// Request images asynchronously so the collection view does not slow down/lag
let task = NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: { (data, response, error) -> Void in
// Check if there is data returned
guard let data = data else {
print("There is no data")
return
}
if let hingeImage = UIImage(data: data){
//Cache images/set key for it
HomepageCollectionViewController.imageCache.setObject(hingeImage, forKey: image.imageUrl!)
// Dispatch to the main queue
dispatch_async(dispatch_get_main_queue(), { () -> Void in
//Hide activity indicator and stop animating
cell.actitivityIndicator.hidden = true
cell.actitivityIndicator.stopAnimating()
//Set images to collection view
cell.collectionViewImage.image = hingeImage
})
}
})
task.resume()
}
}
}
return cell
}

Answer 1

NSCache is the smarter version of NSDictionary class which shares the same API for retrieving, adding or removing items.
Thus, you can delete an item from it using same method as if you do from a dictionary:
HomepageCollectionViewController.imageCache.removeObjectForKey(image.imageUrl!)
You can update your code to remove the image from cache that you are just about to show:
if let myImage = HomepageCollectionViewController.imageCache.removeObjectForKey(image.imageUrl!) as? UIImage {
// myImage was removed from cache.
cell.collectionViewImage.image = myImage
...