ImageOperation: Example of a custom NSOperation.

ImageOperation.m

//
//  ImageOperation.m
//  AsyncImageDemo
//
//  Created by Chris Boyd on 10/18/11.
//  Copyright (c) 2011 ChrisBoyd.net. All rights reserved.
//

#import "ImageOperation.h"

@implementation ImageOperation
@synthesize appDelegate, url;

- (id)init {
    self = [super init];
    if (self != nil)
    {
        self.appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
    }
    return self;
}

- (void)dealloc {
    [url release], url = nil;
    [super dealloc];
}

- (void)main {
    if (self.isCancelled) return;
    if (self.url == nil) return;
    
    // Create path to output images
    NSString *filename = [self.appDelegate sanitizedFilename:self.url];
    NSString *filepath = [[self.appDelegate documentsDirectory] stringByAppendingPathComponent: 
                          [NSString stringWithFormat: @"%@", filename]];
    
    // Download the image
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:self.url]];
    
    // Check for a cancellation
    if (self.isCancelled) return;
    
    // Save the NSData object as a file
    [data writeToFile:filepath atomically:NO];
}

@end