Creating pin-code dialogue

Question

I would like to create a pin-code dialogue, like the one you can switch on on the iPhone.

For those who have not seen it, it consists of four boxes and a number keypad. When you enter a digit, a dot appears in the first box. And so forth. When you hit the delete button, the last dot is removed.

I have this set up as four UITextFields and in my delegate I listen to:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
  [self performSelector:@selector(pickNext:) withObject:textField afterDelay:0.0];
  return YES;
}

The pickNext: method will switch to the next UITextField, like this:

- (void)pickNext:(UITextField*)textField
{
  switch ([textField tag]) {
    case 1:
      [pin2 becomeFirstResponder];
      break;
    case 2:
      [pin3 becomeFirstResponder];
      break;
    case 3:
      [pin4 becomeFirstResponder];
      break;
    case 4:
      [textField resignFirstResponder];
      break;
    default:
      break;
  }
}

This actually works, but the problem for me is that the delete key does not produce any notification when the UITextField is already empty. So I have no way of moving to the previous UITextField.

So does anyone have a better sugestion of how to solve this problem. I'm thinking hidden textfield...??

Answer 1

OK, so I solved it myself. The hidden textfield was the way to go. Even though it is hidden, you can still make it the first responder and the keyboard will pop up.

So to summarize:

In viewDidLoad:

[hidden becomeFirstResponder];

And then I listen for the "Editing Changed" event and update the four visible UITextField with one character each. Like this:

- (IBAction)textChanged:(UITextField*)hiddenField
{
  NSString *hiddenText = hiddenField.text;

  [self setOneTextField:pin1 toString:hiddenText atIndex:0];
  [self setOneTextField:pin2 toString:hiddenText atIndex:1];
  [self setOneTextField:pin3 toString:hiddenText atIndex:2];
  [self setOneTextField:pin4 toString:hiddenText atIndex:3];
}

- (void)setOneTextField:(UITextField*)textField toString:(NSString*)string atIndex:(NSInteger)index
{
  if ([string length] > index)
    textField.text = [string substringWithRange:NSMakeRange(index, 1)];
  else
    textField.text = @""; 
}

To restrict the number of characters in the hidden UITextField to four characters I implement the delegate method "shouldChangeCharactersInRange":

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
  bool okToEdit = YES;

  if (range.location > 3)
  {
    okToEdit = NO;
  } else if (range.location == 3) {
    [self performSelector:@selector(sendPinCodeNotification) withObject:nil afterDelay:0.0];
  }
  return okToEdit;
}

- (void)sendPinCodeNotification
{
  [[NSNotificationCenter defaultCenter] postNotificationName:PINCODE_NOTIFICATION object:[NSString stringWithFormat:@"%@%@%@%@", pin1.text, pin2.text, pin3.text, pin4.text]];
}

And as you can see I send a notification when the fourth digit has been entered.