title: how to check textfield's previous value and modified value
body: <p>I'm new in iphone development.i want to give an alert message if <code>textfield's</code> text is whether change or not.how i can check textfield's text previous values and current values?</p>
  
  <p>my code is</p>
  
  <pre><code>UITextField *txtCon;
  
  NSString *strname;
  
  txtCon.text = @"hello";
  
  strname = txtCon.text;
  
  if(txtCon.text == strname)
  {
  UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Rate on the Appstore!" 
                                                  message:@"changed" 
                                                 delegate:self 
                                        cancelButtonTitle:@"Later" 
                                        otherButtonTitles:@"OK", nil];
  [alert show];
  [alert release];
  }
  else
  {
  UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Rate on the Appstore!" 
                                                  message:@"not changed" 
                                                 delegate:self 
                                        cancelButtonTitle:@"Later" 
                                        otherButtonTitles:@"OK", nil];
  [alert show];
  [alert release];
  }
  </code></pre>