Subclassing NSComboBox to display NSMenu on PopUp
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I want an editable control similar to `NSComboBox`, which have the autocomplete capabilities of `NSComboBox` but the problem with combo box is that the list of values can only be text values. Whereas, I want, when the arrow button of combo box is pressed, it should display a NSMenu (so that I can display icons in front of the text and also can have separator NSMenuItem as one of the items in `NSMenu`).

So, I was planning to subclass `NSComboBox` such that the original list popup of `NSComboBox` is suppressed and instead of that an `NSMenu` is displayed.

But I have no idea where to start with.

Firstly, I am unable to suppress the default popup.
Second, there is no notification for the button press of the combo box, so that I can display my NSMenu.

Any help is greatly appreciated.