How can I extract a URL from a sentence that is in a NSString?

Question

What I'm trying to accomplish is as follows. I have a NSString with a sentence that has a URL within the sentience. I'm needing to be able to grab the URL that is presented within any sentence that is within a NSString so for example:

Let's say I had this NSString

NSString *someString = @"This is a sample of a http://example.com/efg.php?EFAei687e3EsA sentence with a URL within it.";

I need to be able to extract http://example.com/efg.php?EFAei687e3EsA from within that NSString. This NSString isn't static and will be changing structure and the url will not necessarily be in the same spot of the sentence. I've tried to look into the three20 code but it makes no sense to me. How else can this be done?

Answer 1

Use an NSDataDetector:

NSString *string = @"This is a sample of a http://example.com/efg.php?EFAei687e3EsA sentence with a URL within it.";
NSDataDetector *linkDetector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypeLink error:nil];
NSArray *matches = [linkDetector matchesInString:string options:0 range:NSMakeRange(0, [string length])];
for (NSTextCheckingResult *match in matches) {
  if ([match resultType] == NSTextCheckingTypeLink) {
    NSURL *url = [match URL];
    NSLog(@"found URL: %@", url);
  }
}

This way you don't have to rely on an unreliable regular expression, and as Apple upgrades their link detection code, you get those improvements for free.

Answer 2

Edit: I'm going to go out on a limb here and say you should probably use NSDataDetector as Dave mentions. Far less prone to error than regular expressions.

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Take a look at regular expressions. You can construct a simple one to extract the URL using the NSRegularExpression class, or find one online that you can use. For a tutorial on using the class, see here.

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The code you want essentially looks like this (using John Gruber's super URL regex):

NSRegularExpression *expression = [NSRegularExpression regularExpressionWithPattern:@"(?i)\\b((?:[a-z][\\w-]+:(?:/{1,3}|[a-z0-9%])|www\\d{0,3}[.]|[a-z0-9.\\-]+[.][a-z]{2,4}/)(?:[^\\s()<>]+|\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\))+(?:\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\)|[^\\s`!()\\[\\]{};:'\".,<>?«»“”‘’]))" options:NSRegularExpressionCaseInsensitive error:NULL];
NSString *someString = @"This is a sample of a http://example.com/efg.php?EFAei687e3EsA sentence with a URL within it.";
NSString *match = [someString substringWithRange:[expression rangeOfFirstMatchInString:someString options:NSMatchingCompleted range:NSMakeRange(0, [someString length])]];
NSLog(@"%@", match); // Correctly prints 'http://example.com/efg.php?EFAei687e3EsA'

That will extract the first URL in any string (of course, this does no error checking, so if the string really doesn't contain any URL's it won't work, but take a look at the NSRegularExpression class to see how to get around it.