什么时候应该使用NSURL而不是NSString，反之亦然？

这不是有关问题的问题。

This is not a question about a pertinent problem. It's a question by which I try to deepen my understanding of Objective-C or more specific Cocoa Foundation.

在处理从服务器上传和下载文件到我的应用程序时，我总是在使用 NSURL 或 NSString 之间撕裂所有东西路径相关。当然，当有一个现有的API，我只是使用它根据规格。但是当我存储我自己的路径或创建处理他们的自定义类时，我困惑了哪两个是更好的选择。

When dealing with uploading and download files from a server to my apps, I'm constantly torn between using NSURL or NSString for all things path related. Of course when there's an existing API I just use it according to the specs. But when I store my own paths or create custom classes that deal with them, I'm confused which of the two would be the better pick.

NSString 无处不在，它有方便的方法，如 stringByAppendingPathComponent：和 stringByAppendingPathExtension：。我可以通过使用 [NSURL URLWithString：@string] 创建一个新实例，然后调用 [url path] ] 。但是区别是有原因的，对吧？

NSString is used everywhere and it has convenience methods like stringByAppendingPathComponent: and stringByAppendingPathExtension:. I can easily convert to NSURL by creating a new instance with [NSURL URLWithString:@"string"] and the other way around by calling [url path] on an NSURL instance. But the difference is there for a reason, right?

当我看看NSFileManager的头文件时，我的混乱增长。这两个方法非常接近：

My confusion grows when I look at header files of something like NSFileManager. These two methods are pretty close together:

- (BOOL)copyItemAtPath:(NSString *)srcPath toPath:(NSString *)dstPath error:(NSError **)error;
- (BOOL)copyItemAtURL:(NSURL *)srcURL toURL:(NSURL *)dstURL error:(NSError **)error NS_AVAILABLE(10_6, 4_0);

为什么我会选择使用一个，特别是当两者之间的转换如此轻松？为什么苹果会遇到使用这两种数据类型创建近乎相同的API的麻烦？

Why would I choose to use one over the other, especially when conversions between the two are made so easily? And why does Apple go through the trouble of creating near-identical APIs for using both data types?

如果有人更深入地了解何时使用NSURL而不是NSString你自己的类处理文件路径和远程url，请分享！干杯。

If someone has the deeper insight for when to use NSURL instead of NSString for your own classes handling file paths and remote urls, please do share! Cheers.