Recipe: Adding Undo Support

Undo support provides another important component of direct manipulation interfaces. For a simple GUI, this involves little more than returning each object to a previous onscreen position. Cocoa Touch offers the NSUndoManager class to provide a way to reverse user actions.

Creating an Undo Manager

By default, every application window provides a shared undo manager. You can use this shared manager or create your own. The easiest way to hook into the shared manager is to wait until the view has been presented in viewDidAppear: and then point a local instance variable to that shared manager: