On 14 Mar 2012, at 20:12, Seth Willits wrote:
> On Mar 14, 2012, at 3:26 AM, Luc Van Bogaert wrote:
>
>> I would like to implement undo/redo for a model object which in turn is also
>> a ivar backed property of a document object. I'm already using the
>> document's undo manager to undo/redo setting the model object property. Once
>> the property is set, the application has features to change properties of
>> the model object. I'm not sure how to implement undo/redo for the changes of
>> the model object's properties and ivars.
>
>
> My bad. I completely misinterpreted your original post.
>
> You can use the document's undo manager to hold the changes to your object.
> In your model object, you'll need a either a weak reference to the document,
> or a strong reference to an undo manager. Let's assume the latter. When you
> set the custom object property on the document, set that object's undo
> manager to that of the document. (Unset it off of the custom object you're
> replacing.) Inside your custom object's setter methods, you'd handle the undo
> like normal:
>
> - (void)setFoo:(int)foo
> {
> [[[self undoManager] prepareInvocationWithTarget:self] setFoo:_foo];
> _foo = foo;
> }
>
>
> This way both changes to the document and to the custom object are in the
> same undo manager which is attached to the document's window.
>
> Side notes: If you're wondering about having the undo registration in the
> model's setter itself, by doing so you never need a third object to properly
> change the value AND register the undo. To me it felt a little weird to have
> a model have an undo manager since conceptually it seemed to me that should
> be handled at a controller level, but it really does simply the coding, and
> after a whole lot of searching the archives and reading apple documentation
> it seems to be the preferred solution in many cases. It doesn't always have
> to be that way.
>
By "strong reference", I assume you mean I should add an ivar of type
NSUndoManager to my model object to hold a reference to the document's
undoManager, right? If so, I think I understand what you are saying. I will
give this a try. Thanks!
But could you also please explain a little more clearly what you mean with
"weak reference" to the document?
--
Luc Van Bogaert
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