Adding .gitignore file after first repository commit

It happen to me very often to create a git repository and even push it to mu github without first creating a .gitignore file. Specially on Android projects this publishes a lot of unwanted files, like binary and temporary files. For this I found a post on stackoverflow for just that.

From all the post I read this is the one that worked for me (at least now)

http://stackoverflow.com/questions/7927230/remove-directory-from-remote-repository-after-adding-them-to-gitignore

I did this, however in the post is more information about it, please go to the stackoverflow link and if it work for you go ahead a plus it.

git rm --cached `git ls-files -i --exclude-from=.gitignore` 
git commit -m 'Removed all files that are in the .gitignore' 
git push origin master

If you have a better way to do this please leave a comment.