main.dart

import 'dart:math';
import 'package:flutter/material.dart';

class MyFailureApp extends StatefulWidget{

  @override
  State<MyFailureApp> createState() => new MyFailureAppState();

}

class MyFailureAppState extends State<MyFailureApp>{

  var fillerTexts = List<String>.generate(5, (int index) => Random().nextInt(100).toString());

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(
        title: Text("Ayaya"),
        actions: <Widget>[PopupButtonWidget()],
      ),
      body: new Container(
        child: new ListView.builder(
          itemCount: this.fillerTexts.length,
          itemBuilder: (context, int index) => WidgetForListsContent(
              fillerTexts[index])
        ),
      ),
    );
  }
}

class WidgetForListsContent extends StatelessWidget{
  final String name;
  WidgetForListsContent(this.name);

  @override
  Widget build(BuildContext context) {
    return new Card(
      child: new Container(
        padding: EdgeInsets.all(8.0),
        child: new Row(
          children: <Widget>[
            new CircleAvatar(child: new Text(name[0]),),
            new Padding(padding: EdgeInsets.only(right: 10.0)),
            new Text(name,style: TextStyle(fontSize: 20.0),)
          ],
        ),
      ),
    );
  }
}

class PopupButtonWidget extends StatelessWidget {
  const PopupButtonWidget();

  @override
  Widget build(BuildContext context) {
    return Container(
      child: PopupMenuButton<void>(
        onSelected: (_) {
          myChoiceAction(context);
        },
        itemBuilder: (BuildContext context){
          return MyStringsForApp.myChoices.map((String choice){
            return PopupMenuItem<String>(
              value: choice,
              child: Text(choice),
            );
          }).toList();
          },
      )
    );
  }

  void myChoiceAction(context){
    Navigator.push(
      context,
      MaterialPageRoute(builder: (context) => SecondScreen()),
    );
  }
}


// создание роутов для новых экранов
class SecondScreen extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Ti pidor'),
      ),

    );
  }
}

// наполнение попап-окошка
class MyStringsForApp{
  static const String Choice_One = "Choice_1";
  static const String Choice_Two = "Choice_2";
  static const String Choice_Three = "Choice_3";

  static const List<String> myChoices = <String>[
    Choice_One,
    Choice_Two,
    Choice_Three
  ];
}

main() => runApp(MaterialApp(home: MyFailureApp(), debugShowCheckedModeBanner: false,));