Flutter | Navigation bar with createChannels

sample.dart

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: navigationBar(),
    body: body(context),
  );
}

Widget navigationBar() {
  return AppBar(
    automaticallyImplyLeading: true,
    leading: BackButton(color: Theme.of(context).buttonColor),
    backgroundColor: Colors.white,
    title: Text(
      'Select members',
      style: TextStyle(color: Colors.black),
    ),
    actions: [
      TextButton(
        style: ButtonStyle(
            foregroundColor: MaterialStateProperty.all<Color>(
                Theme.of(context).buttonColor)),
        onPressed: () {
          if (_selectedUsers.toList().length < 2) {
            // Don't create a channel if there aren't at least 2 users selected
            return;
          }
          createChannel(
                  [for (final user in _selectedUsers.toList()) user.userId])
              .then((channel) {
            Navigator.pushReplacement(
              context,
              MaterialPageRoute(
                builder: (context) => GroupChannelView(groupChannel: channel),
              ),
            );
          }).catchError((error) {
            print(
                'navigationBar: createChannel: ERROR: $error');
          });
        },
        child: Text(
          "Create",
          style: TextStyle(
            fontSize: 20.0,
            color: Theme.of(context).primaryColor,
          ),
        ),
      )
    ],
    centerTitle: true,
  );
}