使用ASI队列请求,下载图片

参考开发者指南那份Demo，效果如图,ASI强大的功能使用异步队列下载更为简便

代码如下:

//开始队列
- (IBAction)fetchThreeImages:(id)sender
{
    // UI清空
    [imageView1 setImage:nil];
    [imageView2 setImage:nil];
    [imageView3 setImage:nil];
    self.progressIndicator.progress = 0.0;
    self.imageProgressIndicator1.progress = 0.0;
    self.imageProgressIndicator2.progress = 0.0;
    self.imageProgressIndicator3.progress = 0.0;
    
    // 初始化队列
    if (!networkQueue) {
        networkQueue = [[ASINetworkQueue alloc] init];    
        // 设置最大并发数 默认为-1 无限制
        [networkQueue setMaxConcurrentOperationCount:10];
    }
    failed = NO;
    // 重制队列
    [networkQueue reset];
    // 设置队列的进度条
    [networkQueue setDownloadProgressDelegate:progressIndicator];
    // 设置完成方法
    [networkQueue setRequestDidFinishSelector:@selector(imageFetchComplete:)];
    // 设置错误方法
    [networkQueue setRequestDidFailSelector:@selector(imageFetchFailed:)];
    // 显示精确进度
    [networkQueue setShowAccurateProgress:YES];
    
    [networkQueue setDelegate:self];
    
    // 初始化请求
    
    ASIHTTPRequest *request;
    // 设置请求URL
    request = [ASIHTTPRequest requestWithURL:[NSURL URLWithString:@"http://allseeing-i.com/ASIHTTPRequest/tests/images/small-image.jpg"]];
    // 设置下载的目标路径
    [request setDownloadDestinationPath:[[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"girl.png"]];
    // 设置进度条
    [request setDownloadProgressDelegate:imageProgressIndicator1];
    // 自定义用户信息
    [request setUserInfo:[NSDictionary dictionaryWithObject:@"request1" forKey:@"name"]];
    // 将请求加入队列
    [networkQueue addOperation:request];
    
    // 同上
    request = [[ASIHTTPRequest alloc] initWithURL:[NSURL URLWithString:@"http://allseeing-i.com/ASIHTTPRequest/tests/images/medium-image.jpg"]];
    [request setDownloadDestinationPath:[[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"2.png"]];
    [request setDownloadProgressDelegate:imageProgressIndicator2];
    [request setUserInfo:[NSDictionary dictionaryWithObject:@"request2" forKey:@"name"]];
    [networkQueue addOperation:request];
    
    // 同上
    request = [[ASIHTTPRequest alloc] initWithURL:[NSURL URLWithString:@"http://allseeing-i.com/ASIHTTPRequest/tests/images/large-image.jpg"]];
    [request setDownloadDestinationPath:[[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"3.png"]];
    [request setDownloadProgressDelegate:imageProgressIndicator3];
    [request setUserInfo:[NSDictionary dictionaryWithObject:@"request3" forKey:@"name"]];
    [networkQueue addOperation:request];
    
    // 启动队列
    [networkQueue go];
}

// 请求成功后更新UI
- (void)imageFetchComplete:(ASIHTTPRequest *)request
{
    // 从下载路径里读取文件
    UIImage *img = [UIImage imageWithContentsOfFile:[request downloadDestinationPath]];
    NSString *name = [[request userInfo] valueForKey:@"name"];
    
    if (img) {
        if ([name isEqualToString:@"request1"]) {
            [imageView1 setImage:img];
        }else if([name isEqualToString:@"request2"]){
            [imageView2 setImage:img];
        }else if([name isEqualToString:@"request3"]){
            [imageView3 setImage:img];
        }
    }
    
}

// 请求失败后调用
- (void)imageFetchFailed:(ASIHTTPRequest *)request
{
    if (!failed) {
        if ([[request error] domain] != NetworkRequestErrorDomain || [[request error] code] != ASIRequestCancelledErrorType) {
            UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Download failed" message:@"Failed to download images" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [alertView show];
        }
        failed = YES;
    }
}