Control API design strategy: Being asked vs. Telling

Targets macOS
1

I’m wrapping a few Cocoa controls in pure Xojo (NSToolbar, NSToolbarItem, NSToolbarItemGroup, NSTableView, NSOutlineView, NSPredicateEditor, and some more).

I’ve now finished the Toolbar related stuff – I have developed several versions as a test.

Before I start working on the other controls, I have to decide how to translate Cocoa’s delegate / protocol architecture to Xojo. These are the possibilities I could come up with:
– interface: close to Cocoa, the delegate can be a separate class or the control class
– delegate class: close to Cocoa, but the delegate must be a separate class
– events: still kind of like in Cocoa, but the delegate is always the control class
– properties and methods: completely different (NSTableView would have an API very close to Listbox)

The big gap is of course between the first/second/third (“Being asked” – the Cocoa way) and the fourth item (“Telling” – the Xojo way) of my list. What would you prefer as a developer using such a control?

2

This is the approach I use when creating delegates, however when I am using non-delegate protocols (some classes use observers but not delegates) then I use a separate class which raises the events and is designed to be subclassed.