changing subtitle

new ListTile(
              title: new Text("Log In"),
              leading: new Icon(Icons.account_box),
              onTap: () => _signIn()
                  .then((FirebaseUser user) => print(user))
                  .catchError((e) => print(e)),
              subtitle: StreamBuilder(
                stream: FirebaseAuth.instance.onAuthStateChanged,
                builder: (BuildContext context,
                    AsyncSnapshot<FirebaseUser> snapshot) {
                  if (snapshot.connectionState == ConnectionState.waiting) {
                    username = 'loading';
                    return Text(username);
                  } else if (!snapshot.hasData) {
                    username = 'you are not logged in';
                    return Text(username);
                  } else {
                    username = snapshot.data.displayName;
                    return Text(username);
                  }
                },
              ),
            ),
            new ListTile(
              title: new Text("Log Out"),
              leading: new Icon(Icons.account_circle),
              onTap: () => _signOut(),
            ),
//this is the sign in code

  Future<FirebaseUser> _signIn() async {
    GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();
    GoogleSignInAuthentication gSA = await googleSignInAccount.authentication;

    FirebaseUser user = await _auth.signInWithGoogle(
        idToken: gSA.idToken, accessToken: gSA.accessToken);
    print("User Name : ${user.displayName}");
    return user;
  }
//this is the sign out code
 void _signOut() {
    googleSignIn.signOut();
  }