Chapter 39. Undo
The ability to undo the most recent action is familiar from Mac OS X. The idea is that, provided the user realizes soon enough that a mistake has been made, that mistake can be reversed. Typically, a Mac application will maintain an internal stack of undoable actions; choosing Edit → Undo or pressing Command-Z will reverse the action at the top of the stack, and will also make that action available for Redo.
Some iOS apps, too, may benefit from at least a limited Undo facility, and this is not difficult to implement. Some built-in views — in particular, those that involve text entry, UITextField and UITextView (Chapter 23) — implement Undo already. And you can add it in other areas of your app.
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