Two Screens with Three Counters and Print() functions highlight the StatefulWidgets' lifecycle

three_counter_app_with_prints

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

/// Highlights UI while debugging.
import 'package:flutter/rendering.dart' as debug;

void main() => runApp(MyApp());

///
class MyApp extends StatelessWidget {
  ///
  MyApp({super.key}) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   MyApp StatelessWidget created. Its constructor called.');
    }
  }
  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   MyApp build() called!');
    }

    /// Set some of these to true and see what happens.
    /// They're only available in 'debug mode'.
    /// They're to help during development
    assert(() {
      /// Highlights UI while debugging.
      debug.debugPaintSizeEnabled = false;
      debug.debugPaintBaselinesEnabled = false;
      debug.debugPaintPointersEnabled = false;
      debug.debugPaintLayerBordersEnabled = false;
      debug.debugRepaintRainbowEnabled = false;
      debug.debugRepaintTextRainbowEnabled = false;
      return true;
    }());

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: HomePage(),
    );
  }
}

///
class HomePage extends StatefulWidget {
  ///
  HomePage({super.key}) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   HomePage StatefulWidget created. Its constructor called.');
    }
  }

  @override
  State createState() {
    return HomePageState();
  }
}

class HomePageState extends State<HomePage> with CounterState {
  HomePageState() : super() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    super.initState();
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState initState() called.');
    }
    // Take in this State object into this class object
    StateController(this);
  }

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState build() called!');
    }

    return FirstPage();
    return const _FirstPageWithConst();
    return FirstPage(key: UniqueKey());
    return _InheritedWidget(child: const _FirstPageInherited());
    return const _InheritedWidget(child: _FirstPageInherited());
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState deactivate() called.');
    }
    super.deactivate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   HomePageState reassemble() called.');
    }
    super.reassemble();
  }
}

///
/// First Page
///
///
///
class FirstPage extends StatefulWidget {
  ///
  const FirstPage({super.key});

  @override
  State createState() {
    return FirstPageState();
  }
}

///
class FirstPageState extends State<FirstPage> with CounterState {
  ///
  FirstPageState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState initState() called.');
    }
    super.initState();
    // HomePageState is found because its an ancestor on the same branch of the Widget tree.
    homePageState = context.findAncestorStateOfType<HomePageState>()!;
  }

  ///
  late HomePageState homePageState;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState build() called!');
    }
    return Scaffold(
      appBar: AppBar(
        title: Text('Home counter: ${homePageState.counter}'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            FirstCounter(),
//            const FirstCounter(), // See the difference!
            const SizedBox(height: 100),
            Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                const Text(
                  'You have pushed the button this many times:',
                ),
                Text(
                  '$counter',
                  style: Theme.of(context).textTheme.headlineMedium,
                ),
              ],
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          if (kDebugMode) {
            print('>>>>>>>>>>>>>>>>>>>>>>>>>');
            print(
                '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState button pressed. Its setState() called.');
          }
          setState(() {
            counter++;
          });
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
      persistentFooterAlignment: AlignmentDirectional.centerStart,
      persistentFooterButtons: <Widget>[
        TextButton(
          child: const Text(
            'Title Counter',
          ),
          onPressed: () {
            //
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Title Counter' button pressed. _MyHomePageState setState() called.");
            }
            homePageState.counter++;
            homePageState.setState(() {});
          },
        ),
        TextButton(
          child: const Text(
            'Second Page',
          ),
          onPressed: () async {
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Second Page' button pressed. Navigator.push() called.");
            }
            await Navigator.push(
              context,
              MaterialPageRoute<void>(
                builder: (BuildContext context) => SecondPage(),
              ),
            );
            // Update the Title count!
            setState(() {});
          },
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(FirstPage oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageState disposed() called. Counter was $counter');
    }
  }
}

///
/// The First Counter
///
///
class FirstCounter extends StatefulWidget {
  ///
  const FirstCounter({super.key});

  @override
  State createState() {
    return FirstCounterState();
  }
}

///
class FirstCounterState extends State<FirstCounter> with CounterState {
  ///
  FirstCounterState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    super.initState();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState initState() called.');
    }
  }

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState build() called!');
    }
    return Column(
      mainAxisAlignment: MainAxisAlignment.end,
      children: <Widget>[
        const Text(
          'You have pushed the button this many times:',
        ),
        Text(
          '$counter',
          style: Theme.of(context).textTheme.headlineMedium,
        ),
        Align(
          alignment: Alignment.bottomRight,
          child: Padding(
            padding: const EdgeInsets.only(right: 12),
            child: FloatingActionButton(
              heroTag:
                  null, // Fixes 'multiple heroes that share the same tag' error
              onPressed: () {
                if (kDebugMode) {
                  print('>>>>>>>>>>>>>>>>>>>>>>>>>');
                  print(
                      '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState button pressed. Its setState() called.');
                }

                counter++;
                setState(() {});
              },
              child: const Icon(Icons.add),
            ),
          ),
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(FirstCounter oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterState disposed() called. Counter was $counter');
    }
  }
}

///
///  Second Page
///
///
class SecondPage extends StatefulWidget {
  ///
  SecondPage({super.key}) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPage StatefulWidget created. Its constructor called.');
    }
  }
  @override
  State createState() {
    return SecondPageState();
  }
}

///
class SecondPageState extends State<SecondPage> with CounterState {
  ///
  SecondPageState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState initState() called.');
    }
    super.initState();
    // Returns null.
    // HomePageState is on a separate branch of the Widget tree.
    homePageState = context.findAncestorStateOfType<HomePageState>();
    homePageState = context.findRootAncestorStateOfType<HomePageState>();
    // Supply access to the Home Page's State object.
    con = StateController(this);
  }

  ///
  HomePageState? homePageState;

  ///
  late StateController con;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState build() called!');
    }
    return Scaffold(
      appBar: AppBar(
        title: Text('Home counter: ${con.counter}'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text("You're on this second page."),
            const Text('You have pushed the button this many times:'),
            Text(
              '$counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          if (kDebugMode) {
            print('>>>>>>>>>>>>>>>>>>>>>>>>>');
            print(
                '>>>>>>>>>>>>>>>>>>>>>>>>>   Second page FloatingActionButton pressed. Its setState() called.');
          }
          setState(() {
            counter++;
          });
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
      persistentFooterAlignment: AlignmentDirectional.centerStart,
      persistentFooterButtons: <Widget>[
        TextButton(
          child: const Text(
            'Title Counter',
          ),
          onPressed: () {
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Title Counter' button pressed. SecondPageState setState() called.");
            }
            con.counter++;
            setState(() {});
          },
        ),
      ],
    );
  }

  @override
  void deactivate() {
    super.deactivate();
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState deactivate() called.');
    }
  }

  @override
  void didUpdateWidget(SecondPage oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState disposed() called. Counter was $counter');
    }
  }
}

///
/// FirstPage called with const keyword
///
///
///
class _FirstPageWithConst extends StatefulWidget {
  ///
  const _FirstPageWithConst();

  @override
  State createState() {
    return _FirstPageWithConstState();
  }
}

///
class _FirstPageWithConstState extends State<_FirstPageWithConst>
    with CounterState {
  ///
  _FirstPageWithConstState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState initState() called.');
    }
    super.initState();
    // HomePageState is found because its an ancestor on the same branch of the Widget tree.
    homePageState = context.findAncestorStateOfType<HomePageState>()!;
  }

  late HomePageState homePageState;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState build() called!');
    }
    return Scaffold(
      appBar: AppBar(
        title: Text('Home counter: ${homePageState.counter}'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const _FirstCounterWithConst(),
            const SizedBox(height: 100),
            Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                const Text(
                  'You have pushed the button this many times:',
                ),
                Text(
                  '$counter',
                  style: Theme.of(context).textTheme.headlineMedium,
                ),
              ],
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          if (kDebugMode) {
            print('>>>>>>>>>>>>>>>>>>>>>>>>>');
            print(
                '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState button pressed. Its setState() called.');
          }
          setState(() {
            counter++;
          });
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
      persistentFooterAlignment: AlignmentDirectional.centerStart,
      persistentFooterButtons: <Widget>[
        TextButton(
          child: const Text(
            'Title Counter',
          ),
          onPressed: () {
            //
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Title Counter' button pressed. _FirstPageConstState setState() called.");
            }
            homePageState.counter++;
            setState(() {});
          },
        ),
        TextButton(
          child: const Text(
            'Second Page',
          ),
          onPressed: () async {
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Second Page' button pressed. Navigator.push() called.");
            }
            await Navigator.push(
              context,
              MaterialPageRoute<void>(
                builder: (BuildContext context) => SecondPage(),
              ),
            );
            // Update the Title count!
            setState(() {}); // Comment out. Title count won't refresh.
          },
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(_FirstPageWithConst oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageWithConstState disposed() called. Counter was $counter');
    }
  }
}

///
/// FirstCounter called with the const keyword
///
///
class _FirstCounterWithConst extends StatefulWidget {
  ///
  const _FirstCounterWithConst();

  @override
  State createState() {
    return _FirstCounterWithConstState();
  }
}

///
class _FirstCounterWithConstState extends State<_FirstCounterWithConst>
    with CounterState {
  ///
  _FirstCounterWithConstState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    super.initState();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState initState() called.');
    }
  }

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState build() called!');
    }
    return Column(
      mainAxisAlignment: MainAxisAlignment.end,
      children: <Widget>[
        const Text(
          'You have pushed the button this many times:',
        ),
        Text(
          '$counter',
          style: Theme.of(context).textTheme.headlineMedium,
        ),
        Align(
          alignment: Alignment.bottomRight,
          child: Padding(
            padding: const EdgeInsets.only(right: 12),
            child: FloatingActionButton(
              heroTag:
                  null, // Fix 'multiple heroes that share the same tag' error
              onPressed: () {
                if (kDebugMode) {
                  print('>>>>>>>>>>>>>>>>>>>>>>>>>');
                  print(
                      '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState button pressed.');
                }

                counter++;
                setState(() {});
              },
              child: const Icon(Icons.add),
            ),
          ),
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(_FirstCounterWithConst oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterWithConstState disposed() called. Counter was $counter');
    }
  }
}

///
/// FirstPage called with const keyword
/// and indirectly involving an InheritedWidget
///
///
///
class _FirstPageInherited extends StatefulWidget {
  ///
  const _FirstPageInherited();

  @override
  State createState() {
    return _FirstPageInheritedState();
  }
}

///
///  FirstPageState indirectly involving an InheritedWidget
///
///
class _FirstPageInheritedState extends State<_FirstPageInherited>
    with CounterState {
  ///
  _FirstPageInheritedState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState initState() called.');
    }
    super.initState();
    // HomePageState is found because its an ancestor on the same branch of the Widget tree.
    homePageState = context.findAncestorStateOfType<HomePageState>()!;
  }

  late HomePageState homePageState;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState build() called!');
    }
    return Scaffold(
      appBar: AppBar(
        title: const HomeTitle(),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const _FirstCounterInherited(),
            const SizedBox(height: 100),
            Column(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                const Text(
                  'You have pushed the button this many times:',
                ),
                Text(
                  '$counter',
                  style: Theme.of(context).textTheme.headlineMedium,
                ),
              ],
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          if (kDebugMode) {
            print('>>>>>>>>>>>>>>>>>>>>>>>>>');
            print(
                '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState button pressed. Its setState() called.');
          }
          setState(() {
            counter++;
          });
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
      persistentFooterAlignment: AlignmentDirectional.centerStart,
      persistentFooterButtons: <Widget>[
        TextButton(
          child: const Text(
            'Title Counter',
          ),
          onPressed: () {
            //
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Title Counter' button pressed. _FirstPageInheritedState setState() called.");
            }
            homePageState.counter++;
            // Commented out, going back to the First Page, title counter not displayed correctly.
            homePageState.setState(() {});
            // It's incremented, and change displayed here
//            setState(() {});
          },
        ),
        TextButton(
          child: const Text(
            'Second Page',
          ),
          onPressed: () {
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Second Page' button pressed. Navigator.push() called.");
            }
            Navigator.push(
              context,
              MaterialPageRoute<void>(
                builder: (BuildContext context) => _SecondPageInherited(),
              ),
            );
          },
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(_FirstPageInherited oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstPageInheritedState disposed() called. Counter was $counter');
    }
  }
}

//
/// FirstCounter called with the const keyword
/// and involving an InheritedWidget
///
///
class _FirstCounterInherited extends StatefulWidget {
  ///
  const _FirstCounterInherited();

  @override
  State createState() {
    return _FirstCounterInheritedState();
  }
}

///
///  FirstCounterState indirectly calling an InheritedWidget
///
///
class _FirstCounterInheritedState extends State<_FirstCounterInherited>
    with CounterState {
  ///
  _FirstCounterInheritedState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    super.initState();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState initState() called.');
    }
    // HomePageState is found because its an ancestor on the same branch of the Widget tree.
    homePageState = context.findAncestorStateOfType<HomePageState>()!;
  }

  late HomePageState homePageState;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState build() called!');
    }
    // _InheritedWidget is found because its an ancestor on the same branch
    // as this State object on the Widget tree.
    context.dependOnInheritedWidgetOfExactType<_InheritedWidget>();
    return Column(
      mainAxisAlignment: MainAxisAlignment.end,
      children: <Widget>[
        const Text(
          'You have pushed the button this many times:',
        ),
        Text(
          '$counter',
          style: Theme.of(context).textTheme.headlineMedium,
        ),
        Align(
          alignment: Alignment.bottomRight,
          child: Padding(
            padding: const EdgeInsets.only(right: 12),
            child: FloatingActionButton(
              heroTag:
                  null, // Fix 'multiple heroes that share the same tag' error
              onPressed: () {
                if (kDebugMode) {
                  print('>>>>>>>>>>>>>>>>>>>>>>>>>');
                  print(
                      '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState button pressed.');
                }

                counter++;
                // Calling HomePageState to rebuild will call the InheritedWidget
                // _InheritedWidget if it's implemented there.
                // And because this State object called,
                // dependOnInheritedWidgetOfExactType<_InheritedWidget>(),
                // this State object will also rebuild!! Cool!
                homePageState.setState(() {});
                // What does this do all alone?
                //          setState(() {});
              },
              child: const Icon(Icons.add),
            ),
          ),
        ),
      ],
    );
  }

  /// Called if the widget is 'moved' around the Widget tree
  /// or when the State object is to be disposed() called.
  @override
  void deactivate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState deactivate() called.');
    }
    super.deactivate();
  }

  @override
  void didUpdateWidget(_FirstCounterInherited oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   _FirstCounterInheritedState disposed() called. Counter was $counter');
    }
  }
}

///
///  Second Page involving an InheritedWidget
///
///
class _SecondPageInherited extends StatefulWidget {
  _SecondPageInherited() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPage StatefulWidget created. Its constructor called.');
    }
  }
  @override
  State createState() {
    return _SecondPageInheritedState();
  }
}

class _SecondPageInheritedState extends State<_SecondPageInherited>
    with CounterState {
  _SecondPageInheritedState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState created. Its constructor called.');
    }
  }

  @override
  void initState() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState initState() called.');
    }
    super.initState();
    // Supply access to the Home Page's State object.
    con = StateController(this);
  }

  HomePageState? homePageState;
  late StateController con;

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState build() called!');
    }
    return Scaffold(
      appBar: AppBar(
        title: Text('Home counter: ${con.counter}'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text("You're on this second page."),
            const Text('You have pushed the button this many times:'),
            Text(
              '$counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          if (kDebugMode) {
            print('>>>>>>>>>>>>>>>>>>>>>>>>>');
            print(
                '>>>>>>>>>>>>>>>>>>>>>>>>>   Second page FloatingActionButton pressed. Its setState() called.');
          }
          setState(() {
            counter++;
          });
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
      persistentFooterAlignment: AlignmentDirectional.centerStart,
      persistentFooterButtons: <Widget>[
        TextButton(
          child: const Text(
            'Title Counter',
          ),
          onPressed: () {
            if (kDebugMode) {
              print('>>>>>>>>>>>>>>>>>>>>>>>>>');
              print(
                  ">>>>>>>>>>>>>>>>>>>>>>>>>   'Title Counter' button pressed. SecondPageState setState() called.");
            }
            con.counter++;
            con.setState(() {}); // Update count on First Page screen
            setState(() {}); // Update count in this screen
          },
        ),
      ],
    );
  }

  @override
  void deactivate() {
    super.deactivate();
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>');
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState deactivate() called.');
    }
  }

  @override
  void didUpdateWidget(_SecondPageInherited oldWidget) {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState didUpdateWidget() called.');
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState didChangeDependencies() called.');
    }
    super.didChangeDependencies();
  }

  @override
  void activate() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState activate() called.');
    }
    super.activate();
  }

  /// Called during a 'hot reload'
  @override
  void reassemble() {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState reassemble() called.');
    }
    super.reassemble();
  }

  @override
  void dispose() {
    super.dispose();
    if (kDebugMode) {
      print(
          '>>>>>>>>>>>>>>>>>>>>>>>>>   SecondPageState disposed() called. Counter was $counter');
    }
  }
}

///
/// A StatelessWidget made a dependent to an InheritedWidget
///
///
class HomeTitle extends StatelessWidget {
  ///
  const HomeTitle({super.key});

  @override
  Widget build(BuildContext context) {
    if (kDebugMode) {
      print('>>>>>>>>>>>>>>>>>>>>>>>>>   HomeTitle build() called!');
    }
    // _InheritedWidget is found because its an ancestor on the same branch on the Widget tree.
    // You don't have to take in the return InheritedWidget. It's there just for demonstration purposes.
    // ignore: unused_local_variable
    final inheritedWidget =
        context.dependOnInheritedWidgetOfExactType<_InheritedWidget>();
    final homePageState = context.findAncestorStateOfType<HomePageState>();
    String title;
    if (homePageState == null) {
      title = 'Home Page';
    } else {
      title = 'Home counter: ${homePageState.counter}';
    }
    return Text(title);
  }
}

///
/// A simple means to 'preserves state' but spans between Navigator's screens
///
///
class StateController implements State, CounterState {
  /// Must pass a State object but only the first one is saved.
  /// Any other will be ignored.
  factory StateController(CounterState state) =>
      _this ??= StateController._(state);
  StateController._(CounterState state) {
    _state = state;
  }
  static StateController? _this;

  ///
  CounterState get state => _state;
  late CounterState _state;

  @override
  void activate() {}

  @override
  Widget build(BuildContext context) => _state.build(context);

  @override
  BuildContext get context => _state.context;

  @override
  void deactivate() {}

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {}

  @override
  void didChangeDependencies() {}

  @override
  void didUpdateWidget(covariant StatefulWidget oldWidget) {}

  @override
  void dispose() {}

  @override
  void initState() {}

  @override
  bool get mounted => _state.mounted;

  /// Called when a hot reload is performed.
  @override
  void reassemble() {}

  @override
  void setState(VoidCallback fn) => _state.setState(fn);

  @override
  DiagnosticsNode toDiagnosticsNode(
          {String? name, DiagnosticsTreeStyle? style}) =>
      _state.toDiagnosticsNode(name: name, style: style);

  @override
  String toStringShort() => _state.toStringShort();

  @override
  String toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) =>
      _state.toString(minLevel: minLevel);

  @override
  StatefulWidget get widget => _state.widget;

  @override
  int get counter => _state.counter;

  @override
  set counter(int counter) {
    if (counter == _state.counter + 1) {
      _state.counter++;
    }
  }
}

/// Mixin contains a counter
mixin CounterState<T extends StatefulWidget> on State<T> {
  ///
  int counter = 0;
}

class _InheritedWidget extends InheritedWidget {
  const _InheritedWidget({required super.child});
//  _InheritedWidget({required super.child}); // Better to remove the const keyword

  @override
  bool updateShouldNotify(_InheritedWidget oldWidget) => true;
}