iphone：使用NSURLConnection下载网络图片

from: http://www.iblue.cc/2011/04/使用nsurlconnection下载网络图片/
这是一个很基本的demo，直接看代码，你应该可以看得懂。

IconDownloader.h
===============================
@interface IconDownloader :NSObject
{

NSString *imageURLString;

NSMutableData *activeDownload;

NSURLConnection *imageConnection;
}

@property (nonatomic,retain)
NSString *imageURLString;
@property (nonatomic,retain)
NSMutableData *activeDownload;
@property (nonatomic,retain)
NSURLConnection *imageConnection;

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

@end

IconDownloader.m
=====================================
#import"IconDownloader.h"
@implementation IconDownloader

@synthesize activeDownload;
@synthesize imageConnection;

#pragma mark

- (void)dealloc
{
[activeDownloadrelease];

[imageConnectioncancel];
[imageConnectionrelease];

[superdealloc];
}

- (void)startDownload
{
self.activeDownload = [NSMutableDatadata];

// alloc+init and start an NSURLConnection; release on completion/failure
NSURLConnection *conn = [[NSURLConnectionalloc]
initWithRequest:
[NSURLRequestrequestWithURL:
[NSURLURLWithString:imageURLString]]delegate:self];
self.imageConnection = conn;
[conn
release];
}

- (void)cancelDownload
{
[self.imageConnectioncancel];
self.imageConnection =nil;
self.activeDownload =nil;
}

#pragma mark -
#pragma mark Download support (NSURLConnectionDelegate)

//每次成功请求到数据后将调下此方法
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{

//把每次得到的数据依次放到数组中，这里还可以自己做一些进度条相关的效果
[self.activeDownloadappendData: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];
self.activeDownload =nil;
[image
release];

// Release the connection now that it's finished
self.imageConnection =nil;

}
@end