How to use Flutter Riverpod with Date Range Picker

I created "tripsProvider" instance of StateProvider that holds all trip data, like in your case only one value. Home screen watching that provider and displaying data in ListView, when user select item in list I pass index of item and watch that single item on new screen (copy of yours TripScreen). When user update the data of single item I update that list, so update is available on TripScreen and HomeScreen. I also still learning riverpod but hope my answer can help you.

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:intl/intl.dart';

void main() {
  runApp(
    const ProviderScope(
      child: MyApp(),
    ),
  );
}

final tripsProvider = StateProvider<List<Trip>>(
  (ref) => [
    Trip(
      'Test 1',
      DateTimeRange(start: DateTime(2023, 1, 3), end: DateTime(2023, 1, 6)),
    ),
  ],
);

class Trip {
  final String name;
  final DateTimeRange dateTimeRange;

  const Trip(this.name, this.dateTimeRange);
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Riverpod DateRange Picker',
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends ConsumerWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final trips = ref.watch(tripsProvider);

    return Scaffold(
      appBar: AppBar(title: const Text('Riverpod DateRange Picker')),
      body: ListView.builder(
        itemCount: trips.length,
        itemBuilder: (context, index) {
          Trip trip = trips[index];

          return ListTile(
            title: Text(trip.name),
            onTap: () {
              Navigator.push(
                context,
                MaterialPageRoute<void>(
                  builder: (BuildContext context) => TripScreen(index: index),
                ),
              );
            },
          );
        },
      ),
    );
  }
}

class TripScreen extends ConsumerWidget {
  int index;

  TripScreen({Key? key, required this.index}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final trip = ref.watch(tripsProvider)[index];

    void _showDateRangePicker() async {
      final DateTimeRange? result = await showDateRangePicker(
        context: context,
        locale: const Locale('en', 'GB'),
        initialDateRange: trip.dateTimeRange,
        saveText: 'Done',
        firstDate: DateTime(2022, 1, 1),
        lastDate: DateTime(2030, 12, 31),
      );

      if (result != null) {
        print(result);
        Trip updatedTrip = Trip(trip.name, DateTimeRange(start: result.start, end: result.end));

        ref.read(tripsProvider.notifier).update(
          (state) {
            List<Trip> updatedList = [];
            for (int i = 0; i < state.length; i++) {
              if (i == index) {
                updatedList.add(updatedTrip);
              } else {
                updatedList.add(state[i]);
              }
            }
            return updatedList;
          },
        );
      }
    }

    return WillPopScope(
      onWillPop: () {
        Navigator.pop(context);
        return Future.value(false);
      },
      child: Scaffold(
        backgroundColor: Colors.white,
        appBar: AppBar(
          title: Text(trip.name),
        ),
        body: Padding(
          padding: const EdgeInsets.all(16.0),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              IconButton(
                icon: const Icon(Icons.calendar_month),
                onPressed: () {
                  _showDateRangePicker();
                },
              ),
              Text('Start: ${DateFormat('dd/MM/yyyy').format(trip.dateTimeRange.start)}'),
              Text('End: ${DateFormat('dd/MM/yyyy').format(trip.dateTimeRange.end)}'),
            ],
          ),
        ),
      ),
    );
  }
}