封装的一个用来下载图片的类

 

//
// ImageDownloader
// Created by Tracy E on 10-9-5.
// Copyright 2010 tracy.cpp@gmail.com. All rights reserved.
// 

@protocol ImageDownloaderDelegate;

@interface ImageDownloader : NSObject
{
   NSString *imageURL;
   NSMutableData *activeDownload;
   NSURLConnection *imageConnection;

   id <ImageDownloaderDelegate> delegate;
}
@property (nonatomic, retain) NSString *imageURL;
@property (nonatomic, assign) id <ImageDownloaderDelegate> delegate;
@property (nonatomic, retain) NSMutableData *activeDownload;
@property (nonatomic, retain) NSURLConnection *imageConnection;

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

@end


@protocol ImageDownloaderDelegate

- (void)downloader:(ImageDownloader *)downloader DidFinishDownloadImage:(UIImage *)image;

@end


//
// ImageDownloader
// Created by Tracy E on 10-9-5.
// Copyright 2010 tracy.cpp@gmail.com. All rights reserved.
//

#import "ImageDownloader.h" 

@implementation ImageDownloader
@synthesize imageURL;
@synthesize delegate;
@synthesize activeDownload;
@synthesize imageConnection;

#pragma mark

- (void)dealloc
{
   [activeDownload release];
   [imageConnection cancel];
   [imageConnection release];

   [super dealloc];
}

- (void)startDownload
{
   self.activeDownload = [NSMutableData data];
    // alloc+init and start an NSURLConnection; release on completion/failure
   NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:
   [NSURLRequest requestWithURL:
   [NSURL URLWithString:imageURL]] delegate:self];
   self.imageConnection = conn;
   [conn 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 appIcon and clear temporary data/image
   UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];
    // call our delegate and tell it that our icon is ready for display
   [delegate downloader:self DidFinishDownloadImage:image]
   self.activeDownload = nil;
   [image release];
    // Release the connection now that it's finished
   self.imageConnection = nil;
}

@end

//use the imageDownloader 

- (void)viewDidLoad{
    //....
   ImageDownloader *downloader = [[ImageDownloader alloc] init];
   [downloader setDelegate:self];
   downloader.imageURL = imageURLString;
   [downloader startDownload];
   [downloader release];
    //....
}

- (void)downloader:(ImageDownloader *)downloader DidFinishDownloadImage:(UIImage *)image{
    //image did finish download, receive the image here
   if (downloader != nil) {
      [imageView setImage:image];
   }
}