My Unity version is 2020.1.15, the UI Toolkit Version is preview12.
This are some of the errors that appeared right after updateing:
My Unity version is 2020.1.15, the UI Toolkit Version is preview12.
This are some of the errors that appeared right after updateing:
It seams to me that this version of the uibuilder tries to access internal classes of the ui toolkit package.
Can confirm, 2020.1.15, latest UI Toolkit package. A ton of compile errors from the new UI Builder.
Sorry about that. Pulled the trigger a bit too early. UI Builder preview.10 will require com.unity.ui preview.13 (not yet released) to work. For now, please downgrade to UI Builder preview.9.
For everyone’s information: UI Builder preview.10 is now working in my Unity 2020.1.15f1
Not for me. Waiting patiently for UITK preview 13.
Are you using UI Toolkit (com.unity.ui) package on 2020.1? Does UI Builder preview.10 work in a project if you don’t install com.unity.ui?
No errors if com.unity.ui isn’t installed, only if it is.
Got it. We should have a fix soon. In the meantime, please stay on com.unity.ui.builder 1.0.0-preview.9
Just a FYI - If you already updated to preview 10 (As I had). You can simply update the ProjectDir/Packages/manifest.json to have “com.unity.ui.builder”: “1.0.0-preview.9”.
You can also select previous versions right in the Package Manager, all you need to do is click on show previous versions.

Ohhh, I couldn’t find that as an option, good to know!
Fixed with UIToolkit preview 13
For me also needed to change the Unity version from 2020.1.12 to 2020.1.17 because there were still 10 same errors.
Indeed, as mentioned in the CHANGELOG, UI Builder requires at least
I have compilation error CS0103 in Unity 2020.3.0f1
it works in 2020.2.7f
I used UIBuilder 1.1.0.preview-12
The UI Builder just got an update, can you try with that one? It’s fixing some compilation errors that were reported here on the Forum.