I am trying add the import Esri.ArcGISExtras 1.1, But I can't.
Is there any reference should be added in the project?
All beta questions should be logged in the Early Adopter Community. I'll give you a suggestion here for something to try, but please continue the discussion by creating a new post in the Early Adopter Community - https://earlyadopter.esri.com/home.html
I suggest that you ensure you have run the post installer for the kit that you are trying to run this against. It sounds like the QML plugins did not end up inside the Qt kit you are building with.
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