How to cache images for a tableview? - ios

Question

I have the following code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
//P1
UITableViewCell *cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"Cell Identifier"] autorelease];
cell.textLabel.text = [photoNames objectAtIndex:indexPath.row];
//Check if object for key exists, load from cache, otherwise, load
id cachedObject = [_cache objectForKey:[photoURLs objectAtIndex:indexPath.row]];
if (cachedObject == nil) {
//IF OBJECT IS NIL, SET IT TO PLACEHOLDERS
cell.imageView.image = cachedObject;
[self setImage:[UIImage imageNamed:#"loading.png"] forKey:[photoURLs objectAtIndex:indexPath.row]];
[cell setNeedsLayout];
} else {
//fetch imageData
dispatch_async(kfetchQueue, ^{
//P1
NSData *imageData = [NSData dataWithContentsOfURL:[photoURLs objectAtIndex:indexPath.row]];
dispatch_async(dispatch_get_main_queue(), ^{
cell.imageView.image = [UIImage imageWithData:imageData];
[self setImage:cell.imageView.image forKey:cell.textLabel.text];
[cell setNeedsLayout];
});
});
}
return cell;
}
Other than this, the viewDidLoad method fetches from the web, the json result from flickr, to populate a photoNames and photoURLs. Im trying to cache already downloaded images into a local NSDictionary. The problem is that the images arent loaded. Not even the loading.png placeholder image.

Answer 1

You want to save it in the app's Documents directory:
NSData *imageData = UIImagePNGRepresentation(newImage);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *imagePath =[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"%#.png",#"cached"]];
NSLog((#"pre writing to file"));
if (![imageData writeToFile:imagePath atomically:NO])
{
NSLog((#"Failed to cache image data to disk"));
}
else
{
NSLog((#"the cachedImagedPath is %#",imagePath));
}
Then just save the path in your NSMutableDictionary with:
[yourMutableDictionary setObject:theIMagePath forKey:#"CachedImagePath"];
Then retrieve it with something like:
NSString *theImagePath = [yourMutableDictionary objectForKey:#"cachedImagePath"];
UIImage *customImage = [UIImage imageWithContentsOfFile:theImagePath];
I recommend saving the dictionary inside NSUserDefaults.