flutter: animate transition to named route

You need to use onGenerateRoute in your MaterialApp widget.

onGenerateRoute: (settings) {
  if (settings.name == "/someRoute") {
    return PageRouteBuilder(
      settings: settings, // Pass this to make popUntil(), pushNamedAndRemoveUntil(), works
      pageBuilder: (_, __, ___) => SomePage(),
      transitionsBuilder: (_, a, __, c) => FadeTransition(opacity: a, child: c)
    );
  }
  // Unknown route
  return MaterialPageRoute(builder: (_) => UnknownPage());
},