什么是“代表"?在 Objective C 的 iPhone 开发中?

What is a quot;delegatequot; in Objective C#39;s iPhone development?(什么是“代表?在 Objective C 的 iPhone 开发中?)

问题描述

Objective C 的 iPhone 开发中的委托"是什么?

What is a "delegate" in Objective C's iPhone development?

推荐答案

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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，如果您使用 NSURLConnection 类从网站异步下载数据.NSURLConnection 有三个常见的委托:

A delegate allows one object to send messages to another object when an event happens. For example, if you're downloading data from a web site asynchronously using the NSURLConnection class. NSURLConnection has three common delegates:

 - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
 - (void)connectionDidFinishLoading:(NSURLConnection *)connection
 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

当 NSURLConnection 遇到失败、成功完成或收到来自网站的响应时，将分别调用这些委托中的一个或多个.

One or more of these delegates will get called when NSURLConnection encounters a failure, finishes successfully, or received a response from the web site, respectively.

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