看到这个了吗
委托允许一个对象在事件发生时向另一个对象发送消息.例如,如果使用NSURLConnection class从网站异步下载数据.NSURLConnection有三个常见的委托:
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
当NSURLConnection遇到故障、成功完成或收到网站的响应时,其中一个或多个代理将分别被调用.