Cocoa Programming for OS X: The Big Nerd Ranch Guide

Using NSUndoManager

Now that you have a general idea of how your code will interact with the undo manager, let’s look at a more concrete example. Suppose that you are writing a thermostat application. It has a property, undoManager, an instance of NSUndoManager, as well as a method, makeItHotter(), whose inverse is makeItColder(). Here is how you would implement undo for it:

f​u​n​c​ ​m​a​k​e​I​t​H​o​t​t​e​r​(​)​ ​{​
 ​ ​ ​ ​t​e​m​p​e​r​a​t​u​r​e​ ​+​=​ ​1​0​
 ​ ​ ​ ​u​n​d​o​M​a​n​a​g​e​r​.​p​r​e​p​a​r​e​W​i​t​h​I​n​v​o​c​a​t​i​o​n​T​a​r​g​e​t​(​s​e​l​f​)​.​m​a​k​e​I​t​C​o​l​d​e​r​(​)​
 ​ ​ ​ ​s​h​o​w​T​h​e​T​e​m​p​e​r​a​t​u​r​e​(​)​
}​

Two steps are performed: the prepareWithInvocationTarget(_:) method is called on the undo manager. ...