main.dart

  void showMessage(String message) {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text("Error"),
            content: Text(message),
            actions: [
              TextButton(
                child: Text("Ok"),
                onPressed: () {
                  Navigator.of(context).pop();
                },
              )
            ],
          );
        });
  }