ASI下载

    //创建下载请求
    ASIHTTPRequest *request=[[ASIHTTPRequest alloc] initWithURL:[NSURL URLWithString:fileInfo.savePath]];
    request.delegate = self;
    [request setDownloadDestinationPath:[fileInfo targetPath]];//下载完成时的保存地址
    [request setTemporaryFileDownloadPath:fileInfo.tempPath];//临时文件的保存地址
    [request setDownloadProgressDelegate:self];
    [request setNumberOfTimesToRetryOnTimeout:2];
//    [request setShouldContinueWhenAppEntersBackground:YES];
    [request setAllowResumeForFileDownloads:YES];//支持断点续传
    [request setUserInfo:[NSDictionary dictionaryWithObject:fileInfo forKey:@"File"]];//设置上下文的文件基本信息
    [request setTimeOutSeconds:30.0f];

    //开启异步下载
    [request startAsynchronous];

在代理中处理数据：

- (void)requestStarted:(ASIHTTPRequest *)request{
    NSLog(@"开始了!");
}

- (void)request:(ASIHTTPRequest *)request didReceiveResponseHeaders:(NSDictionary *)responseHeaders{

    NSLog(@"收到回复了！");
}

- (void)request:(ASIHTTPRequest *)request didReceiveBytes:(long long)bytes{
    //更新进度
}

- (void)requestFinished:(ASIHTTPRequest *)request{
    NSLog(@"下载结束了！");
}

- (void)requestFailed:(ASIHTTPRequest *)request{
    //下载失败
}