Asynch TableViewCell Images

Events.h

//
//  Events.h
//  TWI
//
//  Created by Shaun Harrison on 3/18/09.
//  Copyright enormego 2009. All rights reserved.
//

#import <UIKit/UIKit.h>

enum EventType {
	// Other Events
	
	EventImageLoaded,
	EventSmallImageLoaded,
	EventThumbnailImageLoaded,
}; typedef int EventType;

@interface Events : NSObject {

}

+ (void)addObserver:(id)observer selector:(SEL)selector event:(EventType)type;
+ (void)addObserver:(id)observer selector:(SEL)selector object:(id)object event:(EventType)type;

+ (void)removeObserver:(id)observer event:(EventType)type;

+ (void)postEvent:(EventType)type;
+ (void)postEvent:(EventType)type object:(id)object;
	
@end

Events.m

//
//  Events.m
//  TWI
//
//  Created by Shaun Harrison on 3/18/09.
//  Copyright enormego 2009. All rights reserved.
//

#import "Events.h"

#define eventNameFromType(type) [NSString stringWithFormat:@"kTWINotification-%d",(type)]

@implementation Events

+ (void)addObserver:(id)observer selector:(SEL)selector event:(EventType)type {
	[Events addObserver:observer selector:selector object:nil event:type];
}

+ (void)addObserver:(id)observer selector:(SEL)selector object:(id)object event:(EventType)type {
	[[NSNotificationCenter defaultCenter] addObserver:observer selector:selector name:eventNameFromType(type) object:nil];
}

+ (void)removeObserver:(id)observer event:(EventType)type {
	[[NSNotificationCenter defaultCenter] removeObserver:observer name:eventNameFromType(type) object:nil];
}

+ (void)postEvent:(EventType)type {
	[[self class] postEvent:type object:nil];
}

+ (void)postEvent:(EventType)type object:(id)object {
	[object retain];
	if(![NSThread isMainThread]) {
		[self performSelectorOnMainThread:@selector(postEventOnMainThread:) withObject:[NSArray arrayWithObjects:[NSNumber numberWithInt:type],object,nil] waitUntilDone:YES];
	} else {
		[[NSNotificationCenter defaultCenter] postNotificationName:eventNameFromType(type) object:object];
	}
	[object release];
}


+ (void)postEventOnMainThread:(NSArray*)info {
	[[NSNotificationCenter defaultCenter] postNotificationName:eventNameFromType([[info objectAtIndex:0] intValue]) object:info.count > 1 ? [info objectAtIndex:1] : nil];
}

@end

Post.m

- (UIImage*)thumbnailImage {
	if(!thumbnailImageURL) return nil;
	
	NSData* imageData = [[EGOCache currentCache] dataForKey:[[thumbnailImageURL description] md5]];
	
	if(!imageData) {
		@synchronized(self) {
			if(!loadingThumbnailImage) {
				[self performSelectorInBackground:@selector(loadThumbnailImage) withObject:nil];
				loadingThumbnailImage = YES;
			}
		}
		
		return nil;
	} else {
		return [UIImage imageWithData:imageData];
	}
}

- (void)loadThumbnailImage {
	NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
	
	ASIHTTPRequest* request = [[ASIHTTPRequest alloc] initWithURL:thumbnailImageURL];
	[request start];
	
	NSData* imageData = [request responseData];
	if(imageData) {
		[[EGOCache currentCache] setData:imageData forKey:[[thumbnailImageURL description] md5] withTimeoutInterval:604800];
		[Events postEvent:EventThumbnailImageLoaded object:self];
	}
	
	[request release];
	
	[pool release];
}

TableViewCell.m

- (void)thumbnailLoaded:(NSNotification*)aNotification {
	if(aNotification.object != post) return;
	if(post.postType == PostImage) {
		self.imageView.image = post.thumbnailImage;
	} else {
		self.imageView.image = nil;
	}
	
	[self setNeedsLayout];
	//[self setNeedsDisplay];
}

- (void)setPost:(Post*)aPost {
	[post release];
	post = [aPost retain];

	[Events removeObserver:self event:EventThumbnailImageLoaded];
	[Events addObserver:self selector:@selector(thumbnailLoaded:) object:post event:EventThumbnailImageLoaded];

	self.textLabel.text = [post.text stringByReplacingOccurrencesOfString:@"<br />" withString:@""];
	
	if(post.postType == PostImage) {
		self.imageView.image = post.thumbnailImage;
	} else {
		self.imageView.image = nil;
	}
}

- (void)dealloc {
	[Events removeObserver:self event:EventThumbnailImageLoaded];
	[post release];
    [super dealloc];
}

TableViewController.m

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
	static NSString *CellIdentifier = @"PostCell";
	
	PostCell *cell = (PostCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
	if (cell == nil) {
		cell = [[[PostCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease];
	}
	
	// Configure the cell.
	Post* post;
	if(indexPath.row < postsArray.count) {
		post = [postsArray objectAtIndex:indexPath.row];
	} else {
		post = nil;
	}
	
	cell.post = post;
	cell.alternate = indexPath.row % 2 == 0 ? NO : YES;
	cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
	cell.selectionStyle = UITableViewCellSelectionStyleGray;
	
	return cell;
}