On 20/08/2009, at 5:17 AM, Paul Bruneau wrote:
In summary, it seemed like a Long Way to Go just to let my new
Entrance objects know who their document is. In my future is the
fact that Entrances will have FrameModules, which may contain a
Door, which will contain an array of Cutouts and so I am looking at
3-4 more generations of Model object types, each of which must a
similar way to get to the Document's Undo Manager.
Is this the right way?
This can be awkward, it's true.
The most general way I've found to handle this is to give each object
in a tree of objects a back pointer to its owner or container.
Naturally this back pointer mustn't be retained or you'll get a retain
cycle, but any time you add an object to another, the added object's
back pointer is set. The top level object's back pointer points to the
document, or top level controller which owns it, and so there is a
path from any object to the root, which has an undo manager. Then it's
a simple matter to give any object its own -undoManager method (which
always merely invokes its owner's -undoManager method, and so on).
I'd also take issue with the code you posted. As an IBAction method,
it should probably not be setting up the undo task. Instead it should
just set the relevant property(s) of the object it's dealing with, and
those property methods should do the necessary with the undo manager.
The action method is a good place to set the action name though. This
way if there are several steps involved in doing something, like
setting a series of properties, all the steps get undone as needed. It
also means that properties are inherently undoable, and code from
anywhere can call them and be undoable. In your example, if code calls
-removeObject: directly, it won't be undoable.
--Graham
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