[DatePickerThemeData] doesn't allow changes to the sub-header styling #160591

import 'package:flutter/material.dart';

void main() => runApp(const DatePickerApp());

class DatePickerApp extends StatelessWidget {
  const DatePickerApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      restorationScopeId: 'app',
      home: DatePickerExample(restorationId: 'main'),
      theme: ThemeData(
        colorScheme: ColorScheme.light(onSurface: Colors.orange),
        datePickerTheme: DatePickerThemeData(
          backgroundColor: Colors.white,
          // Add button style to set text color to black
          cancelButtonStyle: ButtonStyle(
            foregroundColor: WidgetStatePropertyAll(Colors.black),
          ),
          confirmButtonStyle: ButtonStyle(
            backgroundColor: WidgetStatePropertyAll(Colors.blue),
            foregroundColor: WidgetStatePropertyAll(Colors.white),
          ),
          dayBackgroundColor: WidgetStateProperty.resolveWith((states) {
            if (states.contains(WidgetState.selected)) {
              return Colors.blue;
            }
            return Colors.transparent;
          }),
          dayForegroundColor: WidgetStateProperty.resolveWith((states) {
            if (states.contains(WidgetState.selected)) {
              return Colors.white;
            }
            return Colors.black;
          }),
          headerBackgroundColor: Colors.blue,
          headerForegroundColor: Colors.white,
          inputDecorationTheme: InputDecorationTheme(
            labelStyle: TextStyle(
              color: Colors.black,
              fontSize: 16,
              fontWeight: FontWeight.w500,
            ),
            isDense: true,
            floatingLabelBehavior: FloatingLabelBehavior.auto,
            border: OutlineInputBorder(),
          ),
          todayBackgroundColor: WidgetStateProperty.resolveWith(
            (states) {
              if (states.contains(WidgetState.selected)) {
                return Colors.blue;
              }
              return Colors.transparent;
            },
          ),
          todayForegroundColor: WidgetStateProperty.resolveWith(
            (states) {
              if (states.contains(WidgetState.selected)) {
                return Colors.white;
              }
              return Colors.blue;
            },
          ),

          weekdayStyle: const TextStyle(color: Colors.black),
          yearBackgroundColor: WidgetStateProperty.resolveWith(
            (states) {
              if (states.contains(WidgetState.selected)) {
                return Colors.blue;
              }
              return Colors.transparent;
            },
          ),
          yearForegroundColor: WidgetStateProperty.resolveWith(
            (states) {
              if (states.contains(WidgetState.selected)) {
                return Colors.white;
              }
              return Colors.black;
            },
          ),
          yearOverlayColor: WidgetStatePropertyAll(Colors.blue),
        ),
      ),
    );
  }
}

class DatePickerExample extends StatefulWidget {
  const DatePickerExample({super.key, this.restorationId});

  final String? restorationId;

  @override
  State<DatePickerExample> createState() => _DatePickerExampleState();
}

/// RestorationProperty objects can be used because of RestorationMixin.
class _DatePickerExampleState extends State<DatePickerExample>
    with RestorationMixin {
  // In this example, the restoration ID for the mixin is passed in through
  // the [StatefulWidget]'s constructor.
  @override
  String? get restorationId => widget.restorationId;

  final RestorableDateTime _selectedDate =
      RestorableDateTime(DateTime(2021, 7, 25));
  late final RestorableRouteFuture<DateTime?> _restorableDatePickerRouteFuture =
      RestorableRouteFuture<DateTime?>(
    onComplete: _selectDate,
    onPresent: (NavigatorState navigator, Object? arguments) {
      return navigator.restorablePush(
        _datePickerRoute,
        arguments: _selectedDate.value.millisecondsSinceEpoch,
      );
    },
  );

  @pragma('vm:entry-point')
  static Route<DateTime> _datePickerRoute(
    BuildContext context,
    Object? arguments,
  ) {
    return DialogRoute<DateTime>(
      context: context,
      builder: (BuildContext context) {
        return DatePickerDialog(
          restorationId: 'date_picker_dialog',
          initialEntryMode: DatePickerEntryMode.calendarOnly,
          initialDate: DateTime.fromMillisecondsSinceEpoch(arguments! as int),
          firstDate: DateTime(2021),
          lastDate: DateTime(2022),
        );
      },
    );
  }

  @override
  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    registerForRestoration(_selectedDate, 'selected_date');
    registerForRestoration(
        _restorableDatePickerRouteFuture, 'date_picker_route_future');
  }

  void _selectDate(DateTime? newSelectedDate) {
    if (newSelectedDate != null) {
      setState(() {
        _selectedDate.value = newSelectedDate;
        ScaffoldMessenger.of(context).showSnackBar(SnackBar(
          content: Text(
              'Selected: ${_selectedDate.value.day}/${_selectedDate.value.month}/${_selectedDate.value.year}'),
        ));
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: OutlinedButton(
          onPressed: () {
            _restorableDatePickerRouteFuture.present();
          },
          child: const Text('Open Date Picker'),
        ),
      ),
    );
  }
}