I’ve downgraded my project to Unity 2020.3.35f (to use DOTS), which doesn’t yet have UI Toolkit built in, which my project also uses. To remedy that, I’ve added the latest version of the UI Toolkit package through the package manager…
However, despite the package being installed and everything compiling okay, Unity doesn’t see the UIDocument class. The GameObject which has the UIDocument attached shows it as a missing component. Is there anything else I need to do to get UI Toolkit working under 2020.3.35f?
There is a log of things going on between version, and downgrades are not supported. The GUID identifying the class was changed between the version you were using and 2020.3 : in the newer version of unity, you could go in the in window->UI Toolkit-> package asset conversion before transferring your assets to 2020.3. If this doesn’t work, you will have to create some new UIDocuments, PanelSettings and assign the proper values inside.
Ugh. What a mess!
I think I am going to forego experimenting with DOTS at this time.