问题:

I am trying to build a homebrew web brower to get more proficient at Cocoa. I need a good way to validate whether the user has entered a valid URL. I have tried some regular expressions but NSString has some interesting quirks and doesn't like some of the back-quoting that most regular expressions I've seen use.

回答1:

You could start with the + (id)URLWithString:(NSString *)URLString method of NSURL, which returns nil if the string is malformed.

If you need further validation, you can use the baseURL, host, parameterString, path, etc methods to give you particular components of the URL, which you can then evaluate in whatever way you see fit.

回答2:

I've found that it is possible to enter some URLs that seem to be OK but are rejected by the NSURL creation methods. So we have a method to escape the string first to make sure it's in a good format. Here is the meat of it:

NSString *escapedURLString =
    NSMakeCollectable(CFURLCreateStringByAddingPercentEscapes(NULL,
      (CFStringRef)URLString,
      (CFStringRef)@"%+#",  // Characters to leave unescaped
      NULL,
      kCFStringEncodingUTF8));