how to implement undo using NSUndoManager? (newbie question)

Question

Im trying to add an NSUndoManager to my program but im not sure how to register the methods with the manager using :

[myUndoManager registerUndoWithTarget:selector:object:];

what if i have the following method:

-(IBAction)tapButton:(id)sender {
   myFoo++;    
   yourFoo++;    //incrementing integers
   fooFoo++;
}

how can i register this method with the undo manager? the object of the selector (sender) is not what i want to register. I need to decrement myFoo, yourFoo, and fooFoo with a single undo call.

Answer 1

Write another method -(void) decrementIntegers and register that like this:

[undoManager registerUndoWithTarget: self selector: @selector( decrementIntegers ) object: nil];

In this method you need to register your original method again to provide redo:

[undoManager registerUndoWithTarget: self selector: @selector( tapButton: ) object: self];

But a better way to do this would be to use accessors for your integers and do undo registering in there. Something like this:

- (void) setMyFoo: (int) newMyFoo;
{
   if (myFoo != newMyFoo) {
      [[undoManager prepareWithInvocationTarget: self] setMyFoo: myFoo];
      myFoo = newMyFoo;
   }
}