.dart

class CustomerList extends StatelessWidget {

  final List<String> customers; 
  final Function(String) onSelected; 

  CustomerList({@required this.customers, this.onSelected});

  @override
  Widget build(BuildContext context) {

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