On May 31, 2008, at 3:51 AM, Rick Mann wrote:
I've got an NSTreeController and associated view. I use - awakeFromInsert to set default values for the entities created as a result of calling -add.
That's a good place to do that ...
I'd like for one of the fields to take on the same value as the currently-selected entity.
Okay, that's controller-layer-level logic and perfectly reasonable (ie, any serious app using Bindings is likely to need to do that at some point). Point of order, though - "selected instance", not "selected entity". The distinction is important though the mistake is easily interpreted in this context.
Can I get at that from within -awakeFromInsert?
Yes, through some incredible acrobatics, you probably could, but then that would be like walking right up to the MVC design pattern and b**ch-slapping it right in the face. ;-)
The model layer is *not* where this belongs. Why should some instance of your Foo entity care about whether some other instance is selected in some random controller? That kind of logic belongs in the controller layer. A controller is in the best position to know what's selected and what should happen when a new instance of Foo is created.
Must I create my own -add?
Yes. The best place to put this custom -add: action is up to you and your design (as long as it's in a controller), but NSObjectController (such as NSArrayController or NSTreeController) in charge of the Foo instances, I'd do it this way:
1 - Place your user-level action (what's fired as a result of a button or menu action when the user wants to add a Foo) in some primary controller. This would be your app controller if it's a "Cocoa Application" or your [persistent] document controller if it's a "Cocoa [Core Data] Document-Based Application". If it's a top-level user interface action, a good design (IMO) is to have all user actions funnel through one controller for clarity (to the developer).
2 - In a custom NSTreeController subclass specifically suited to all the "library management" of your Foo instances, create a custom - addFooWithNameOfSelectedFoo method (also gives clarity) that is called by your user-level -add: action. This method simply asks "self" for the currently selected Foo instance, then creates and modifies the new Foo instance to taste. This Foo-centric NSTreeController contains all the logic for dealing with your Foo objects, such as - allFoosBelongingToBar: or -removeFoosOlderThanDate: or -fooWithID: etc. In this way, it's now your "Foo Library Manager" and when it comes to Foos, it knows best.
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