Password validation in UITextField in iOS

Question

I have 1 UITextfield for password in my iPhone application.

I want to validate this textfield with the following validation.

• Must be at le

Answer 1

use a regex (NSRegularExpression class has docs on how to write the patten itself) and then :

- (BOOL)textField:(UITextField *)theTextField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    //delete
    if (string.length == 0) {
        return YES;
    }

    if (self.regEx) {
        NSMutableString* check = [NSMutableString stringWithString:theTextField.text];
        [check replaceCharactersInRange:range withString:string];
        NSTextCheckingResult* match = [self.regEx firstMatchInString:check options:0 range:NSMakeRange(0, [check length])];
        if (match.range.length != check.length) {
            return NO;
        }
    }
}

Warning: Restricting the input this way is really confusing for users. You type and type and the character you type just doesnt appear!

I'd maybe go with a small red (!) next to the test field but I'd always allow the input itself!