Learning the iOS 4 SDK for JavaScript Programmers

Using Regular Expressions for Text Search and Replace

As noted in Chapter 8, the Cocoa Touch NSString object does not offer a method to perform search and replace operations with regular expressions (as the JavaScript String object does). Instead, you can use the iOS 4 (or later) NSRegularExpression class to do the job. To demonstrate how this works, I’ll once again use the UITextField example from earlier in this chapter as a basis. The goal of this version will be to strip out any extra spaces between words entered into the text field and display the results in the label below the field. Example 9-20 shows the one new method and two modified methods from Example 9-18.

Example 9-20. Modifications for regular expression search and replace

- (NSString *)stripExtraWhitespace:(NSString *)inputString {
    NSString *result = inputString;

    // One or more whitespace characters
    NSString *whiteSpacePattern = @"\\s+";
    NSString *replacementString = @" ";

    NSError *error = NULL;
    NSRegularExpression *regex =
        [NSRegularExpression regularExpressionWithPattern:whiteSpacePattern
                                                  options:0
                                                    error:&error];
    if (regex == nil) {
        NSLog(@"RegExp Error: %@", [error localizedDescription]);
    } else {
        result =
           [regex stringByReplacingMatchesInString:inputString
                                           options:0
                                             range:NSMakeRange(0, [inputString length])
                                      withTemplate:replacementString];
    }
    return result;
} // UITextField delegate message - (BOOL)textFieldShouldReturn:(UITextField *)textField { [textField resignFirstResponder]; return YES; } - (IBAction)copyInput:(id)sender ...