selecting editor uxml causes error console errors

Hi,
I’m currently working on an editor tool i made using UI Builder preview 18, in Unity 2019.4
I exported this tool multiple times as a unitypackage, when i import it in a fresh project in a newer version of Unity (i tested 2020.3, 2021.1.14, 2021.2.3), and try to open the editor window it fails, giving this error:

And when i select the .uxml file the console has immediately 999+ errors:

I tried importing the lastest verison of UI builder (com.unity.ui) but the error persists

The only time it worked is whe i imported it to a fresh project using Unity 2020.1

I found the cause of the problem while trying to make a new uxml file using ui builder in Unity 2020.2.

It turns out that in the newer version ui builder no longer allows me to add a visual element inside a ListView, and it seems it’s for a good reason, i had it setup this way in the older uxml.

Solution: i just modified the older uxml to use ScrollView instead of ListView, and now it works in all versions

By the way this is for a UI styling tool for UGUI, i’m planning to release it on the assetstore in the near future:
just for a peek, this is the comparison between the IMGUI and the UIToolkit implementations

Old:

New:

Pretty different!

Nice stuff! And thank you for writing about your findings. Indeed we now prevent users from adding elements to a ListView (or its contentContainer) directly, for obvious reasons, sorry you had to find out that way. Everything goes through makeItem and bindItem now, making the contentContainer unavailable.