Flutter Firestore Chat App Problem

I am trying to make a Flutter Firestore Chat Function, i have implemented all Functions and the Chat works fine, but older Messages only show in my Chat Screen if i execute a “Hot Reload” in Flutter. I have tried adding a setState inside my if(snapshot.hasData) section but i only get following error:
https://prnt.sc/FQ3DFonQ1ql_

Heres a pastebin link to my chat screen code:

Can anyone help me?