[NSData dataWithContentsOfURL:url];

[NSURLConnection connectionWithRequest:request delegate:self];

<div>[NSURLConnection sendAsynchronousRequest: request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse <em>response, NSData </em>data, NSError *connectionError) {}];</div>

获取到一部分data的时候就写入沙盒中，然后释放内存中的data。