I’ve had a couple people ask me for the code behind the image loading that’s referenced in my updates for fast scrolling post and I’m making good on a promise to post the code for everyone else to use. It’s shown below:

ImageDownloader.h

//
//  ImageDownloader.h
//  Lobaco
//
//  Created by David Klemke on 14/10/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import
@class Post;

@protocol ImageDownloadDelegate;

@interface ImageDownloader : NSObject {
	Post *post;
	NSIndexPath *indexPathInTableView;
	id  delegate;

	NSMutableData *activeDownload;
	NSURLConnection *imageConnection;
	bool downloadPostImage;
}

@property (nonatomic, retain) Post *post;
@property (nonatomic, retain) NSIndexPath *indexPathInTableView;
@property (nonatomic, assign) id  delegate;
@property bool downloadPostImage;
@property (nonatomic, retain) NSMutableData *activeDownload;
@property (nonatomic, retain) NSURLConnection *imageConnection;

- (void)startDownload;
- (void)cancelDownload;

@end

@protocol ImageDownloadDelegate

-(void)imageDidLoad: (NSIndexPath *)indexPath;

@end

ImageDownloader.m

//
//  ImageDownloader.m
//  Lobaco
//
//  Created by David Klemke on 14/10/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import "ImageDownloader.h"
#import "Post.h"

#define kImageHeight 75

@implementation ImageDownloader

@synthesize post;
@synthesize indexPathInTableView;
@synthesize delegate;
@synthesize activeDownload;
@synthesize imageConnection;
@synthesize downloadPostImage;

#pragma mark

- (void)dealloc
{
	[post release];
	[indexPathInTableView release];
	[activeDownload release];
	[imageConnection cancel];
	[imageConnection release];
	[super dealloc];
}

- (void)startDownload
{
	self.activeDownload = [NSMutableData data];
	//NSLog(@"%@",[post.data objectForKey:@"ProfileImage"]);
	NSURL *url;
	if (downloadPostImage)
	{
		url = [[NSURL alloc] initWithString:[post.data objectForKey:@"PostImage"]];
	}
	else
	{
		url = [[NSURL alloc] initWithString:[post.data objectForKey:@"ProfileImage"]];
	}

	NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:url] delegate:self];
	self.imageConnection = connection;
	[url release];
	[connection release];
}

- (void)cancelDownload
{
	[self.imageConnection cancel];
	self.imageConnection = nil;
	self.activeDownload = nil;
}

#pragma mark -
#pragma mark Download support (NSURLConnectionDelegate)

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.activeDownload appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    // Clear the activeDownload property to allow later attempts
    self.activeDownload = nil;

    // Release the connection now that it's finished
    self.imageConnection = nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // Set Image and clear temporary data/image
    UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];

    if (image.size.width != kImageHeight && image.size.height != kImageHeight)
    {
        CGSize itemSize = CGSizeMake(kImageHeight, kImageHeight);
        UIGraphicsBeginImageContext(itemSize);
        CGRect imageRect = CGRectMake(0.0, 0.0, itemSize.width, itemSize.height);
        [image drawInRect:imageRect];
		if ([self downloadPostImage])
		{
			self.post.postImage = UIGraphicsGetImageFromCurrentImageContext();
		}
		else
		{
			self.post.profileImage = UIGraphicsGetImageFromCurrentImageContext();
		}
        UIGraphicsEndImageContext();
    }
    else
    {
		if ([self downloadPostImage])
		{
			self.post.postImage = image;
		}
		else
		{
			self.post.profileImage = image;
		}
    }

    self.activeDownload = nil;
    [image release];

    // Release the connection now that it's finished
    self.imageConnection = nil;

    // call our delegate and tell it that our icon is ready for display
    [delegate imageDidLoad:self.indexPathInTableView];
}

@end

There’s definitely room for improvement in there (you can remove some of the application specific logic) but it works well and I never had an issue with it. Let me know if you run into any problems though!

About the Author

David Klemke

David is an avid gamer and technology enthusiast in Australia. He got his first taste for both of those passions when his father, a radio engineer from the University of Melbourne, gave him an old DOS box to play games on.

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