iPhone：使用NSURL请求异步下载数据，而不是[NSData data with CONTENTS ofURL]

嗨，我是个新手，我正试图从googleapi网页下载地理编码数据。我是这样做的：代码：

        NSMutableString *urlStr = [[NSMutableString alloc] initWithString:temp];
        NSMutableString *address = [[NSMutableString alloc] initWithString:l.Address];
        [address appendString:@" "];
        [address appendString:l.CityName];
        [address appendString:@" "];
        [address appendString:l.State];
        [address appendString:@" "];
        [address appendString:l.PostalCode];
        NSArray *addressArray = [address componentsSeparatedByString:@" "];
        [address release];
        NSString *a = [addressArray componentsJoinedByString:@"+"];
        [urlStr appendString:a];
        [urlStr appendString:@"&sensor=false"];
        NSURL *url = [[NSURL alloc] initWithString:[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
        NSData *data = [NSData dataWithContentsOfURL:url];

它工作得很好，但问题是它锁定了我的GUI，因为它是同步完成的

有人建议我使用NSURLrequest异步执行此操作。所以我去了苹果的网站。从那里我看到了他们的榜样。然而，我还是被卡住了。如何将上面的同步请求代码转换为异步请求？到目前为止，这是我所拥有的，但我不确定这是否有效。。。。。。有点困惑。。。有人能用这个密码告诉我正确的方向吗

        NSURL *url = [[NSURL alloc] initWithString:[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
        //create NSURL request for asynchronous processing
        NSURLRequest *theRequest = [NSURLRequest requestWithURL:url
                                                  cachePolicy:NSURLRequestUseProtocolCachePolicy
                                              timeoutInterval:60.0];

        NSURLConnection *theConnection= [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

        if (theConnection) 
           {
            receivedData = [[NSMutableData data] retain];
           }
        else
           {
            // Inform the user that the connection failed.
           }

根据代码的结构，您可能希望在成功完成（ConnectionDiFinishLoading:）或失败（connection:didFailWithError:）时操作或通知其他对象（委托、通知）