How to access a private class in another class ?

[Wizi8914]

In a project I'm trying to get the textureState variable but this one is of type class which is inside another class I asked several people but each one didn't know how to answer or they asked me to try things which didn't work

[tennox]

I think using an access widener is the way to go:
https://www.fabricmc.net/wiki/tutorial:accesswideners

see also #578