Cómo validar textFormfield en el cambio de texto Flutter

class HomeScreen extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(),
          body: Center(
            child: TextFormField(
              autovalidateMode: AutovalidateMode.onUserInteraction,
            ),
          ),
        );
      }
    }
Sourav Maurya