BottomNavigationWithProvider2.dart

import "package:flutter/material.dart";
import "package:flutter/widgets.dart";
import "package:provider/provider.dart";

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => GlobalState()),
      ],
      child: MaterialApp(
        title: 'Flutter 예제',
        theme: ThemeData(
          primarySwatch: Colors.green,
        ),
        home: MyHomePage(),
      ),
    );
  }
}

// 단순 함수,변수 공유용으로 사용
class GlobalState with ChangeNotifier {
  bool isBottomNavigate = true;
  int nClick = 0;

  // page 이동
  void goPage(int n) {
    isBottomNavigate = false;
    nClick++;
    fnPageMove(n);
  }

  // Function 변수들
  late Function fnPageMove;
  late Function fnPage2_setMesageInfo = (String s) {};
}

class _OnePage extends StatefulWidget {
  @override
  _OnePageState createState() {
    return _OnePageState();
  }
}

class _OnePageState extends State<_OnePage> with AutomaticKeepAliveClientMixin {
  late GestureDetector gestureDetector;

  // Setting to true will force the tab to never be disposed. This could be dangerous.
  @override
  bool get wantKeepAlive => true;

  @override
  void initState() {
    return super.initState();
  }

  @override
  Widget build(BuildContext context) {
    var c = context.watch<GlobalState>();
    gestureDetector = GestureDetector(
        onTap: () {
          c.goPage(1);
        },
        child: Text(
          "Tab2로 이동",
          style: TextStyle(fontSize: 30),
        ));

    return gestureDetector;
  }
}

class _TwoPage extends StatefulWidget {
  @override
  _TwoPageState createState() {
    return _TwoPageState();
  }
}

class _TwoPageState extends State<_TwoPage> with AutomaticKeepAliveClientMixin {
  // Setting to true will force the tab to never be disposed. This could be dangerous.
  @override
  bool get wantKeepAlive => true;
  ValueNotifier<String> _data = ValueNotifier<String>("");
  late GlobalState c;

  @override
  void initState() {
    return super.initState();
  }

  @override
  Widget build(BuildContext context) {
    // build에서 초기화해야 한다.
    c = context.watch<GlobalState>();
    c.fnPage2_setMesageInfo = setMessageInfo;
    setDefaultInfo();

    return ValueListenableBuilder(
        valueListenable: _data,
        builder: (ctx, String s, child) {
          return GestureDetector(
              onTap: () {},
              child: Text(
                "${s}",
                style: TextStyle(color: Colors.blue, fontSize: 30),
              ));
        });
  }

  void setMessageInfo(String s) {
    _data.value = s;
  }

  void setDefaultInfo() {
    if (c.isBottomNavigate == false) {
      setMessageInfo("위젯 클릭으로 이동. ${c.nClick}");
      c.isBottomNavigate = true;
    } else {
      setMessageInfo("하단메뉴로 이동.");
      c.isBottomNavigate = true;
    }
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() {
    return _MyHomePageState();
  }
}

class _MyHomePageState extends State<MyHomePage> {
  late List<Widget> _items;

  late GlobalState c;

  ValueNotifier<int> _param = ValueNotifier<int>(0);

  @override
  void initState() {
    _items = [_OnePage(), _TwoPage()];
  }

  int _selectedIndex = 0;

  @override
  Widget build(BuildContext context) {
    // build에서 초기화해야 한다.
    c = context.watch<GlobalState>();
    c.fnPageMove = _onTap;

    return Scaffold(
      appBar: AppBar(
        title: Text("Flutter Learning"),
      ),
      body: ValueListenableBuilder(
        valueListenable: _param,
        builder: (ctx, int n, child) {
          return Center(child: _items[n]);
        },
      ),
      bottomNavigationBar: _showBottomNav(),
    );
  }

  Widget _showBottomNav() {
    return ValueListenableBuilder(
      valueListenable: _param,
      builder: (ctx, n, child) {
        return BottomNavigationBar(
          items: [
            BottomNavigationBarItem(
              icon: Icon(Icons.abc),
              label: '1',
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.numbers_rounded),
              label: '2',
            )
          ],
          currentIndex: _param.value,
          selectedItemColor: Colors.green,
          unselectedItemColor: Colors.grey,
          onTap: _onTap,
        );
      },
    );
  }

  void _onTap(int index) {
    _param.value = index;

    if (_param.value == index && index == 1) {
      c.fnPage2_setMesageInfo("현재 선택된 상태에서 click함.");
    }
  }
}