第一步

/*************异步请求的代理方法[start]****************/
-(void)toRequestData:(NSString *)user_id
{
    [MBProgressHUD showHUDAddedTo:self.view animated:YES];

    //第一步，创建url
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@/%@?access_token=%@&friend_id=%@", service_url, _getFriendInfo, user_id, access_token, user_id]];

    //第二步，创建请求
    NSURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];

    //第三步，连接服务器
    connectionInfo = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    [connectionInfo start];
}

第二步

#pragma mark 网络连接出错时调用
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    [MBProgressHUD hideHUDForView:self.view animated:YES];
    [MBProgressHUD showHUD:self text:[error localizedDescription]];
}

第三步

#pragma mark 服务器的数据已经接收完毕时调用
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    [MBProgressHUD hideHUDForView:self.view animated:YES];