Only allow letters and numbers for a UITextField

Question

I have a signup view controller where the user needs to enter an email address, a username, and a password.

For the username and password fields, right now you can currently sign up with a username like "user%$&" and a password like "password%^&$". I don't want people to be able to use these special characters.

I want to make it so that the username and password fields can only be submitted with alphanumeric characters aka letters and numbers. I have found some methods to do this, but they are confusing and I need this to work specifically with my code.

Here is some of the code that I perform when a user has entered an email, username, and password and they press the submit button:

NSString *user = [_usernameEntry text];
NSString *pass = [_passwordEntry text];
NSString *email = [_emailEntry text];

self.userSubmittedUsername = user;

if ([user length] < 4 || [pass length] < 4) {

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Invalid Entry" message:@"Username and Password must both be at least 4 characters long." delegate:self cancelButtonTitle:@"Okay" otherButtonTitles:nil];

    [alert show];

} else if ([email length] < 8) {

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Invalid Entry" message:@"Please enter your email address." delegate:self cancelButtonTitle:@"Okay" otherButtonTitles:nil];

    [alert show];

} else {

I would just like to add another else if into the above code and have it show an alert view if there are any characters that are NOT letters or numbers.

Thanks.

Answer 1

If you really want to restrict user from entering special characters, then probably the best way is to use shouldChangeCharactersInRange: method

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if(textField==YOUR_USER_NAME_TEXTFIELD || textField == YOUR_PASSWORD_TEXTFIELD)
    {

        NSCharacterSet *myCharSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"];
        for (int i = 0; i < [string length]; i++)
        {
            unichar c = [string characterAtIndex:i];
            if (![myCharSet characterIsMember:c])
            {
                return NO;
            }
        }

        return YES;
    }

    return YES;
}

This will restrict the user from entering the special characters. As rmaddy pointed out, it is always good to do this kind of validation when data entry happens.

PS: Make sure you set the delegate for your textfields.