UitextField shifts control to next textField upon using keyboard input

I am new to iPhone programming. I have two textfields in iPhone with numberPad Keyboard type and i am trying to implement a simple logic that on typing a single digit using numberPadKeyBoard, the control should shift to next textField i.e. second textfield should become FirstResponder. I don't know how to implement this. Pl开发者_如何学Cease guys any help would be appreciated.

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- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

if(textField == urFirstTextField) { 
[urFirstTextField resignFirstResponder];
[urSecondtextField becomeFirstResponder];

}

}

UPDATE

    - (BOOL)textFieldShouldBeginEditing:(UITextField *)textField {
   if(textField != urFirstTextField)
    {
        [textField resignFirstResponder];
        [urFirstTextField becomeFirstResponder];
        return NO;
    }
       return YES;
}

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Suppose you have 2 text field textField1 and textField2 then implement the delgate methods of the UITextFieldDelegate as

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
      if(textField == textField1)
           {
              [textField1 resignFirstResponder];
              [textField2 becomeFirstResponder];
           }
      return YES;
}

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go through the delegate method of UITextField named "textField:shouldChangeText:inRange:" ..... check the length of your textField and make second textField as first responder before returning YES;

Or you can play with a lot of other delegate methods defined