Question

I have a simple app that helps recruiters collect information while at an event. One form field was for a phone number, and I wanted a simple way to reformat the phone number as the user types.

The phone number should evolve as the user types, so sample output for a string of numbers should look like this:

1
1 (20)
1 (206) 55
1 (206) 555-55
1 [phone]

Or alternatively, if the user didn’t enter a 1 before the area code, the phone number would evolve like this:

(20)
(206) 55
(206) 555-55
[phone]

If the phone number is too long, then it should just show a plain string of numbers:

20655555555555555

Answer 1

Here’s what I did: the UITextFieldDelegate handles the textField:shouldChangeCharactersInRange :replacementString: method by getting the text of the UITextField, and running a little method that I wrote:

-(void)updatePhoneNumberWithString:(NSString *)string {

    NSMutableString *finalString = [NSMutableString new];
    NSMutableString *workingPhoneString = [NSMutableString stringWithString:string];

    if (workingPhoneString.length > 0) {
    //This if statement prevents errors when the user deletes the last character in the textfield.

        if ([[workingPhoneString substringToIndex:1] isEqualToString:@"1"]) {
        //If the user typed a "1" as the first digit, then it's a prefix before the area code.
            [finalString appendString:@"1 "];
            [workingPhoneString replaceCharactersInRange:NSMakeRange(0, 1) withString:@""];
        }

        if (workingPhoneString.length < 3) {
        //If the user is dialing the area code...
            [finalString appendFormat:[NSString stringWithFormat:@"(%@)", workingPhoneString]];

        } else if (workingPhoneString.length < 6) {
        //If the user is dialing the 3 digits after the area code...
            [finalString appendFormat:[NSString stringWithFormat:@"(%@) %@", 
                                       [workingPhoneString substringWithRange:NSMakeRange(0, 3)], 
                                       [workingPhoneString substringFromIndex:3]]];

        } else if (workingPhoneString.length < 11) {
        //If the user is dialing the last 4 digits of the phone number...
            [finalString appendFormat:[NSString stringWithFormat:@"(%@) %@-%@", 
                                       [workingPhoneString substringWithRange:NSMakeRange(0, 3)], 
                                       [workingPhoneString substringWithRange:NSMakeRange(3, 3)],
                                       [workingPhoneString substringFromIndex:6]]];
        } else {
        //If the user's typed in a bunch of characters, then just show the full string.
            finalString = phoneString;
        }

        phoneNumberField.text = finalString;
    } else {
    //If the user changed the textfield to contain no text at all...
        phoneNumberField.text = @"";
    }

}

Hope this helps you!