Quick and dirty UIImageView with networking

UIImageView+Network.h

//
//  UIImage+Network.h
//  Fireside
//
//  Created by Soroush Khanlou on 8/25/12.
//
//

#import <UIKit/UIKit.h>

@interface UIImageView(Network)

@property (nonatomic, copy) NSURL *imageURL;

- (void) loadImageFromURL:(NSURL*)url placeholderImage:(UIImage*)placeholder cachingKey:(NSString*)key;

@end

UIImageView+Network.m

//
//  UIImageView+Network.m
//
//  Created by Soroush Khanlou on 8/25/12.
//
//

#import "UIImageView+Network.h"
#import "FTWCache.h"
#import <objc/runtime.h>

static char URL_KEY;


@implementation UIImageView(Network)

@dynamic imageURL;

- (void) loadImageFromURL:(NSURL*)url placeholderImage:(UIImage*)placeholder cachingKey:(NSString*)key {
	self.imageURL = url;
	self.image = placeholder;
	
	NSData *cachedData = [FTWCache objectForKey:key];
	if (cachedData) {   
 	   self.imageURL   = nil;
 	   self.image      = [UIImage imageWithData:cachedData];
	   return;
	}

	dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
	dispatch_async(queue, ^{
		NSData *data = [NSData dataWithContentsOfURL:url];
		
		UIImage *imageFromData = [UIImage imageWithData:data];
		
		[FTWCache setObject:data forKey:key];

		if (imageFromData) {
			if ([self.imageURL.absoluteString isEqualToString:url.absoluteString]) {
				dispatch_sync(dispatch_get_main_queue(), ^{
					self.image = imageFromData;
				});
			} else {
//				NSLog(@"urls are not the same, bailing out!");
			}
		}
		self.imageURL = nil;
	});
}

- (void) setImageURL:(NSURL *)newImageURL {
	objc_setAssociatedObject(self, &URL_KEY, newImageURL, OBJC_ASSOCIATION_COPY);
}

- (NSURL*) imageURL {
	return objc_getAssociatedObject(self, &URL_KEY);
}

@end

You're only caching in downloaded NSData, but you never use that cached objects to save unneeded downloads.

Try adding this code before the dispatch code:

NSData *cachedData = [FTWCache objectForKey:key];
if (cachedData) {   
    self.imageURL   = nil;
    self.image      = [UIImage imageWithData:cachedData];
} else {
    dispatch ...
}

Ah, good call, my bad. Updated.

How to call your code from outside class

@shashankshandilya

just call it from your targeted UIImageView
ex:
[cell.imageView loadImageFromURL:(NSURL_)url placeholderImage:(UIImage_)placeholder cachingKey:(NSString*)key ];

I use your image loading and the loading and image replace things are very good - big thx for that.
My problem is that scrolling in uicollectionview is not that smooth. Is there any performance issue with my cellForItemAtIndexPath-Method?

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{

VideoCell *cell = (VideoCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"VideoCell" forIndexPath:indexPath];

VideoOnDemandMovie *movie = (VideoOnDemandMovie *)[_displayedMoviesArray objectAtIndex:indexPath.row];

[cell.myImageView loadImageFromURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@/%@",_imagePathSystemValue,movie.image]] placeholderImage:[UIImage imageNamed:@"fallback_movie.png"] cachingKey:movie.movieId];    
    return cell;
}

@khanlou Thanks for sharing. Is there any fix for smooth scrolling in UICollectionView. There is little stuck while scrolling.
@mweidinger

I just googling around and see you code looks pretty good 👍

But I'm just doubt is it the problem if some of my UITableViewCell will going to load the same source of image at the same time right before the first one have been loaded and cache.

It would be nice if you can help clarify what will happen.