How to ignore all but one folder in Git?

Question

git

Suppose the project has the following structure:

I only need to track changes in the dev directory.
In .gitignore I write like this:

*
!/dev/

But it doesn't work. dev is ignored. How can the problem be solved?
UPD.
It turned out something like this:

# gitignore
/*.*
/*/*
!/dir1/dir11
!/dir2/dir21
!/dir3/dir31
!/dir4/*

Answer 1

You * match any file in any folder.
As a result , the dev folder is not ignored, but all files in it are ignored because they match the * rule .
You can do this:

# игнорируем всё в корне
/*
# кроме папки /dev
!/dev

Answer 2

can just do git init in dev folder?

Answer 3

Try

*
/!dev/