Problems with generic delegates(UICamera.onDrag,UICamera.onScroll,etc.).
Since I update the NGUI to 3.7.1 , there are new generic delegates to replace the old genericEventHandler GameObject.(Pro-tip#2)
So I want to modify my code , I was using the UICamera.genericEventHandler gameobject to handle OnPress,OnDrag and OnScroll message notified by UICamera in old version,and it works well.
Now I change my code using the UICamera.onPress,UICamera.onDrag and UICamera.onScroll delegates and problems come in.
The UICamera.onPress works well, but the UICamera.onDrag and UICamera.onScroll did not be called when mouse dragged or hovered on empty area(with no collider).
I suspected that some other delegates in UICamera may have the same problem -- process mouse or touch with empty target(no collider), while these problem would not happen when using the old UICamera.genericEventHandler.
After my experience, the UICamera.genericEventHandler cannot be null(you can even set an empty GameObject to it),otherwise the UICamera generic delegates would not be called properly.