title: How can I know Text changes for textboxes without Textchanged event
body: <p>In my C# Windows form MyForm I have some TextBoxes.
  In these TextBoxes, we have to detect if the TextChanged event occurs,
  if there're changes in these TextBoxes and click close button, it will ask if we want to cancel the changes when we close the form.
  However, when I run the MyForm, I can't know text change for each textbox caused by user typing for without textchanged event property.
  But I am thinking how do I make the TextBox's TextChanged know the
  event cuased by user typing without textchanged event?
  Thanks for help.
  Sorry for my English.</p>