.dart

class CustomerList extends StatelessWidget {

  final List<String> customers; 

  CustomerList({@required this.customers});

  @override
  Widget build(BuildContext context) {

    return ListView.builder(
        itemCount: customers.length,
        itemBuilder: (context, index) {
          final customer = customers[index]; 
          return ListTile(
            title: Text(customer), 
            onTap: () {
              Navigator.push(context, MaterialPageRoute(
                builder: (context) => CustomerDetailScreen(customer: customer)
              ));
            },
          );
        }
      );
    
  }
}



class CustomerListScreen extends StatelessWidget {

  final customers = ["Alex", "John", "Bryan", "Jerry", "Mary"];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Customers")
      ), 
      body: CustomerList(customers: customers)
    );
  }
}