如何检查文件是否存在于特定的 URL? [英] How to check if a file exists at particular URL?

问题描述

如何检查网站上是否存在文件?我将 NSURLConnection 与我的 NSURLRequest 和一个 NSMutableData 对象一起使用来存储 didReceiveData: 委托方法中返回的内容.在 connectionDidFinishingLoading: 方法中，我将 NSMutableData 对象保存到文件系统.都好.除了:如果该文件在网站上不存在，我的代码仍然会运行，获取数据并保存文件.

How do I check if a file exists on a web site? I am using NSURLConnection with my NSURLRequest and an NSMutableData object to store what comes back in the didReceiveData: delegate method. In the connectionDidFinishingLoading: method I then save the NSMutableData object to the file system. All good. Except: if the file does not exist at the website, my code still runs, gets data and saves a file.

如何在我提出下载请求之前检查文件是否存在?

How can I check the file is there before I make download request?

推荐答案

实现connection:didReceiveResponse:，会在connection:didReceiveData:之前调用.

响应应该是一个 NSHTTPURLResponse 对象——假设您正在发出一个 HTTP 请求.因此，您可以检查 [response statusCode] == 404 以确定文件是否存在.

The response should be an NSHTTPURLResponse object — suppose you're issuing an HTTP request. You can therefore check [response statusCode] == 404 to determine if the file exists or not.

另请参阅检查 NSURL 是否返回 404.

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