title: UndoManager in iphone sdk
body: <p>I want to apply the Undo &amp; Redo operations in my app.
  I read the apple document as well as googled it but not get the proper solution.
  In my app I apply lot of image operations on UIImage &amp; I want to store each state &amp; apply Undo -Redo accordingly.
  How to use UndoManager? How it Works?
  Please share some links regarding this or links for tutorials of undo manager.
  If anyone knows it, then please help me.
  Thanks in advance.</p>