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

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//
//  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

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//
//  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!

Technology

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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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