How do I use NSRange with this NSString?

问题:

I have the following NSString:

productID = @"com.sortitapps.themes.pink.book";

At the end, "book" can be anything.... "music", "movies", "games", etc.

I need to find the third period after the word pink so I can replace that last "book" word with something else. How do I do this with NSRange? Basically I need this:

partialID = @"com.sortitapps.themes.pink.";

回答1:

You can try a backward search for the dot and use the result to get the desired range:

NSString *str = @"com.sortitapps.themes.pink.book";
NSUInteger dot = [str rangeOfString:@"." options:NSBackwardsSearch].location;

NSString *newStr =
   [str stringByReplacingCharactersInRange:NSMakeRange(dot+1, [str length]-dot-1)
                                withString:@"something_else"];

回答2:

You can use -[NSString componentsSeparatedByString:@"."] to split into components, create a new array with your desired values, then use [NSArray componentsJoinedByString:@"."] to join your modified array into a string again.

回答3:

Well, although this isn't a generic solution for finding characters, in your particular case you can "cheat" and save code by doing this:

[productID stringByDeletingPathExtension];

Essentially, I'm treating the name as a filename and removing the last (and only the last) extension using the NSString method for this purpose.