How do you detect words that start with “@” or “#” within an NSString?

Question

I'm building a Twitter iPhone app, and it needs to detect when you enter a hashtag or @-mention within a string in a UITextView.

How do I find all words preceded by the "@" or "#" characters within an NSString?

Thanks for your help!

Answer 1

You can use NSRegularExpression class with a pattern like #\w+ (\w stands for word characters).

NSError *error = nil;
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"#(\\w+)" options:0 error:&error];
NSArray *matches = [regex matchesInString:string options:0 range:NSMakeRange(0, string.length)];
for (NSTextCheckingResult *match in matches) {
    NSRange wordRange = [match rangeAtIndex:1];
    NSString* word = [string substringWithRange:wordRange];
    NSLog(@"Found tag %@", word);
}

Answer 2

You can break a string into pieces (words) by using componentsSeparatedByString: and then check the first character of each one.

Or, if you need to do it while the user is typing, you can provide a delegate for the text view and implement textView:shouldChangeTextInRange:replacementText: to see typed characters.