flutter CheckedPopupMenuItem选择项目后保持菜单打开

Question

我试图使菜单保持打开状态，以便我可以一次选择多个类别，而不必在每次选择后都返回到页面。

如果它可以像Excel过滤器数据（或Libreoffice Autofilter）一样工作，那就太完美了

添加了屏幕截图

任何想法将不胜感激！

current app my goal example

代码：

import 'package:flutter/material.dart';

void main() {   return runApp(MaterialApp(
    home: MenuDemo(),   )); }

class MenuDemo extends StatefulWidget {   const MenuDemo({Key key}) : super(key: key);

  static const String routeName = '/material/menu';

  @override   MenuDemoState createState() => new MenuDemoState(); }

class MenuDemoState extends State<MenuDemo> {   final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  final String _checkedValue1 = 'One';   final String _checkedValue2 = 'Two';   final String _checkedValue3 = 'Free';   final String
_checkedValue4 = 'Four';   List<String> _checkedValues;

  @override   void initState() {
    super.initState();
    _checkedValues = <String>[_checkedValue3];   }

  void showInSnackBar(String value) {
    _scaffoldKey.currentState
        .showSnackBar(new SnackBar(content: new Text(value)));   }

  void showCheckedMenuSelections(String value) {
    if (_checkedValues.contains(value))
      _checkedValues.remove(value);
    else
      _checkedValues.add(value);

    showInSnackBar('Checked $_checkedValues');   }

  bool isChecked(String value) => _checkedValues.contains(value);

  @override   Widget build(BuildContext context) {
    return new Scaffold(
        key: _scaffoldKey,
        body: Center(
          child: Container(
            width: 250.0,
            child: new ListTile(
                title: const Text(
                  'checklist menu',
                  textAlign: TextAlign.center,
                ),
                trailing: new PopupMenuButton<String>(
                    padding: EdgeInsets.zero,
                    onSelected: showCheckedMenuSelections,
                    itemBuilder: (BuildContext context) =>
                        <PopupMenuItem<String>>[
                          new CheckedPopupMenuItem<String>(
                              value: _checkedValue1,
                              checked: isChecked(_checkedValue1),
                              child: new Text(_checkedValue1)),
                          new CheckedPopupMenuItem<String>(
                              value: _checkedValue2,
                              //enabled: false,
                              checked: isChecked(_checkedValue2),
                              child: new Text(_checkedValue2)),
                          new CheckedPopupMenuItem<String>(
                              value: _checkedValue3,
                              checked: isChecked(_checkedValue3),
                              child: new Text(_checkedValue3)),
                          new CheckedPopupMenuItem<String>(
                              value: _checkedValue4,
                              checked: isChecked(_checkedValue4),
                              child: new Text(_checkedValue4))
                        ])),
          ),
        ));   } }