IPointerClickHandler does not fire if IPointerDownHandler is also implemented in Heirarchy

[Wyntersoft]

Continuing the discussion from IPointerClickHandler does not fire if IPointerDownHandler is also implemented:

@Adrian

And you can run into weird intricacies that you can often only resolve through debugging or experimentation. E.g. in the InputSystemUIInputModule, a IPointerDownHandler on a parent will prevent IPointerClickHandler handlers on children, unless they also have a IPointerDownHandler. I only figured that out by stepping through the code and checking what is happening*.

(*A click requires press and release target game objects to match. An IPointerDownHandler will take precedence over the IPointerClickHandler to set the event’s pointerPress target. This means that on release, the pointerPress will never match the click handler’s game object and a click cannot trigger. Adding an empty IPointerDownHandler with the IPointerClickHandler fixes this, as it will set the pointerPress to the right target on down.)

Two years later, I just lost an afternoon independently discovering this…

[Adrian]

Yeah, uGUI is unfortunately in maintenance mode, as Unity focuses on UI Toolkit. So I don’t think behavioral issues like this will ever get fixed.

Actually, uGUI has practically been in maintenance mode since its release, receiving no major new features besides a few tweaks here and there. It took years and a few aborted attempts for uGUI to be finally released and then Unity almost immediately abandoned it to work on the next GUI system, which has also taken a decade to materialize.

Unfortunately, UI Toolkit is not quite ready yet for runtime UI. The big missing pieces being world-space UI and better animation/shading support. So we’ll be stuck with uGUI and its idiosyncrasies for a while longer.