Check if the user is logged in Flutter & firebase auth |

That didn't work for me so this is what I did:

FirebaseAuth.instance.currentUser().then((firebaseUser){
  if(firebaseUser == null)
   {
     //signed out
   }
   else{
    //signed in
  }
});

Use the currentUser() method:

if (await FirebaseAuth.instance.currentUser() != null) {
    // signed in
} else {

}