How to catch the plugin window focus loss event in mac OS?

[vasyan]

I made a drop-down list of presets with the ability to specify favorites.



It closes when you select a preset, or by clicking the mouse to any other place in the plugin window. I would also like the list to close also when the focus of the plugin window is lost. If in Windows this is solved by reacting to the WM_KILLFOCUS message, then in mac OS, unfortunately, I do not know how to implement it.
I would appreciate any help on this issue.