AsyncImageView.h

//
//  AsyncImageView.h
//  Postcard
//
//  Created by markj on 2/18/09.
//  Copyright 2009 Mark Johnson. You have permission to copy parts of this code into your own projects for any use.
//  www.markj.net
//

// See
// http://www.markj.net/iphone-asynchronous-table-image/
// http://blogs.oreilly.com/iphone/2008/12/useful-core-graphics-functions.html


#import <UIKit/UIKit.h>


@interface AsyncImageView : UIView {
	//could instead be a subclass of UIImageView instead of UIView, depending on what other features you want to 
	// to build into this class?

	NSURLConnection* connection; //keep a reference to the connection so we can cancel download in dealloc
	NSMutableData* data; //keep reference to the data so we can collect it as it downloads
	//but where is the UIImage reference? We keep it in self.subviews - no need to re-code what we have in the parent class
	
}

- (void)loadImageFromURL:(NSURL*)url;
- (UIImage*) image;

@end

AsyncImageView.m

//
//  AsyncImageView.m
//  Postcard
//
//  Created by markj on 2/18/09.
//  Copyright 2009 Mark Johnson. You have permission to copy parts of this code into your own projects for any use.
//  www.markj.net
//

#import "AsyncImageView.h"


// This class demonstrates how the URL loading system can be used to make a UIView subclass
// that can download and display an image asynchronously so that the app doesn't block or freeze
// while the image is downloading. It works fine in a UITableView or other cases where there
// are multiple images being downloaded and displayed all at the same time. 

@implementation AsyncImageView

- (void)dealloc {
	[connection cancel]; //in case the URL is still downloading
	[connection release];
	[data release]; 
    [super dealloc];
}


- (void)loadImageFromURL:(NSURL*)url {
	if (connection!=nil) { [connection release]; } //in case we are downloading a 2nd image
	if (data!=nil) { [data release]; }
	
	NSURLRequest* request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
	connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; //notice how delegate set to self object
	//TODO error handling, what if connection is nil?
}


//the URL connection calls this repeatedly as data arrives
- (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)incrementalData {
	if (data==nil) { data = [[NSMutableData alloc] initWithCapacity:2048]; } 
	[data appendData:incrementalData];
}

//the URL connection calls this once all the data has downloaded
- (void)connectionDidFinishLoading:(NSURLConnection*)theConnection {
	//so self data now has the complete image 
	[connection release];
	connection=nil;
	if ([[self subviews] count]>0) {
		//then this must be another image, the old one is still in subviews
		[[[self subviews] objectAtIndex:0] removeFromSuperview]; //so remove it (releases it also)
	}
	
	//make an image view for the image
	UIImageView* imageView = [[[UIImageView alloc] initWithImage:[UIImage imageWithData:data]] autorelease];
	//make sizing choices based on your needs, experiment with these. maybe not all the calls below are needed.
	imageView.contentMode = UIViewContentModeScaleAspectFit;
	imageView.autoresizingMask = ( UIViewAutoresizingFlexibleWidth || UIViewAutoresizingFlexibleHeight );
	[self addSubview:imageView];
	imageView.frame = self.bounds;
	[imageView setNeedsLayout];
	[self setNeedsLayout];

	[data release]; //don't need this any more, its in the UIImageView now
	data=nil;
}

//just in case you want to get the image directly, here it is in subviews
- (UIImage*) image {
	UIImageView* iv = [[self subviews] objectAtIndex:0];
	return [iv image];
}

@end