Flutter gsheets read and post

I have a flutter app that writes to gsheets through a gscript. I need for it to also read all the data from the 2 workbooks that I am using to post data. I also have a problem with google sign in. I can sign in correctly, but when I sign in the first time and go back to the first page and I click on the button to sign in again, I am not taken to the next page that I need to go to. The idea is that when I click on the submit button, The app will post to a db and a log, when I click on update, it updates the db and posts to the log, and all the items on screen get updated, with the values entered, since I need for the items that I enter to appear on screen.