How to do it...

Open the existing stopwatch project to get started:

1. Named routes are referenced as strings. To reduce the potential for error, add some constants to the top of both stopwatch.dart and login_screen.dart:

class LoginScreen extends StatefulWidget {
  static const route = '/login';

class StopWatch extends StatefulWidget {
  static const route = '/stopwatch'; 

2. These routes need to be wired up in MaterialApp so that they can be fed to the app's Navigator. 
3. Open main.dart and update the MaterialApp's constructor so that it includes these pages:

return MaterialApp(
  routes: {
    '/': (context) => LoginScreen(),
    LoginScreen.route: (context) => LoginScreen(),
    StopWatch.route: (context) => StopWatch(),
  },
  initialRoute: '/',
);

4. Now, we can invoke this route. Open login_screen.dart and scroll to the _validate method. Replace the existing navigator code...