Custom NSViewController representedObject doesn't update when view selection changes

Question

I've got a custom NSViewController that's also an NSOutlineViewDataSource. I also have a window with an NSOutlineView bound to an instance of my view controller as the data source, and the NSOutlineView bound to the view: property of the custom view controller.

The controller fills the outline view fine. However, selections within the view don't automatically update the representedObject property of the controller. The only thing that seems to trigger a change in representedObject is when I call setRepresentedObject: directly... which sort of defeats the purpose.

Any idea why that might be? representedObject is supposed to update automatically, right? Thanks in advance...

Answer 1

If I understand your question, you are not understanding what representedObject is for. The representedObject is the model object that represents all the data that a view controller is displaying. It is not the current selection of a view showing a collection of content. The representedObject for your custom top level view controller would be an NSArray or other collection class which contains the set of data you are displaying in your view controller. Changing the representedObject for your custom top level view controller should have the effect of swapping out for an entirely new data set if the pattern is being used correctly.

Typically the view controllers for the individual elements in a tabular type view would each have their own representedObject and this object would not change. For example if you were using an NSCollectionView each element in the view is controlled by an NSCollectionViewItem which is a subclass of NSViewController. The representedObject for each NSCollectionViewItem tells it what data to present in its little view.

NSOutlineView and its superclass NSTableView are different in that their cells are often NSCells rather than full fledged NSViews unless you choose to use them this way in Mac OS X 10.7 or newer. Even in this case, you don't typically have an NSViewController subclass managing each cell. So the view controller representedObject pattern is not used at the level of the individual element that the user would select. If what you want is to track the NSOutlineView's selection, there are many NSTableView methods that let you do this.