Basically I have three different Core Data entities (A, B, C) and A contains a set of Bs and B contains a set of Cs. These three entities are, however, quite different from each other and they don't have common methods to access each other's children or the values to be displayed in the view.
I'm trying to display these three enties in an NSOutlineView. There's propably other solutions too but I came up with two different ones:
Implementing NSOutlineViewDataSource protocol and handling each of the entities differently.
Consolidate the classes with categories and add common (transient) methods/properties for the NSOutlineView to use. These methods/properties get their actual values from the model entities' properties.
I chose the second option and added getters for the children and the display value. This way, however, the Key-Value Observing does not work anymore and changes in the model are not reflected to the view. I understand why, but I'm not sure how to solve this the right way. I was thinking of some way to be notified of the actual model value changes and forward them to the view.
Is there any easy way to forward those notifications or should I consider some other alternative?
In short, I need to display different kinds of entities in an NSOutlineView and I don't want to mess the model.
After some trial and error, I found out that creating a custom data source is really that simple and decided to go with the first choice. Also, with drag & drop support this feels much more natural way.
The only issue was with outlineView:setObjectValue:forTableColumn:byItem: for which one needs to specify column identifier references. I feel that undirect dependencies are always something one should avoid, but this is a small matter in comparison to making this work nicely.