Replace navigation_and_routing with a new sample (#832)

* move snippets into old_snippets directory

* add new navigation_and_routing sample

* add copyright headers

* Apply #827 to old_snippets/ directory and upgrade them to null safety

* Code review comments

- Move Guard class into parser.dart
- Move usage of guards from Delegate to RouteInformationParser
- Rename delegate to SimpleRouterDelegate

* clean up imports

* refactor settings screen, fix bug

* avoid conflicting paths /books/new and /books/1 - rename to book/1

* dispose fields in _BookstoreState class

* remove /books path

This was causing problems

* add comment

* Change BookstoreAuthScope and BookstoreAuthScope to InheritedNotifier

* fix warnings

* Make the initial route configurable, set to '/signin'

* Enable deep linking

https://flutter.dev/docs/development/ui/navigation/deep-linking

* use path URL strategy on the web.

* remove TODO, add comment

navigation_and_routing/old_snippets/router/router.dart

@@ -0,0 +1,276 @@
+// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Full sample that shows a custom RouteInformationParser and RouterDelegate
+/// parsing named routes and declaratively building the stack of pages for the
+/// [Navigator].
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(const BooksApp());
+}
+
+class Book {
+  final String title;
+  final String author;
+
+  Book(this.title, this.author);
+}
+
+class BooksApp extends StatefulWidget {
+  const BooksApp({Key? key}) : super(key: key);
+
+  @override
+  State<StatefulWidget> createState() => _BooksAppState();
+}
+
+class _BooksAppState extends State<BooksApp> {
+  final BookRouterDelegate _routerDelegate = BookRouterDelegate();
+  final BookRouteInformationParser _routeInformationParser =
+      BookRouteInformationParser();
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp.router(
+      title: 'Books App',
+      routerDelegate: _routerDelegate,
+      routeInformationParser: _routeInformationParser,
+    );
+  }
+}
+
+class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
+  @override
+  Future<BookRoutePath> parseRouteInformation(
+    RouteInformation routeInformation,
+  ) {
+    final uri = Uri.parse(routeInformation.location ?? '');
+    // Handle '/'
+    if (uri.pathSegments.isEmpty) {
+      return SynchronousFuture(BookRoutePath.home());
+    }
+
+    // Handle '/book/:id'
+    if (uri.pathSegments.length == 2 && uri.pathSegments[0] == 'book') {
+      var remaining = uri.pathSegments[1];
+      var id = int.tryParse(remaining);
+      if (id != null) {
+        return SynchronousFuture(BookRoutePath.details(id));
+      }
+    }
+
+    // Handle unknown routes
+    return SynchronousFuture(BookRoutePath.unknown());
+  }
+
+  @override
+  RouteInformation? restoreRouteInformation(BookRoutePath configuration) {
+    if (configuration.isUnknown) {
+      return const RouteInformation(location: '/404');
+    }
+    if (configuration.isHomePage) {
+      return const RouteInformation(location: '/');
+    }
+    if (configuration.isDetailsPage) {
+      return RouteInformation(location: '/book/${configuration.id}');
+    }
+    return null;
+  }
+}
+
+class BookRouterDelegate extends RouterDelegate<BookRoutePath>
+    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
+  @override
+  final GlobalKey<NavigatorState> navigatorKey;
+
+  Book? _selectedBook;
+  bool show404 = false;
+
+  final List<Book> books = [
+    Book('Left Hand of Darkness', 'Ursula K. Le Guin'),
+    Book('Too Like the Lightning', 'Ada Palmer'),
+    Book('Kindred', 'Octavia E. Butler'),
+  ];
+
+  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>();
+
+  @override
+  BookRoutePath get currentConfiguration {
+    if (show404) {
+      return BookRoutePath.unknown();
+    }
+    return _selectedBook == null
+        ? BookRoutePath.home()
+        : BookRoutePath.details(books.indexOf(_selectedBook!));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Navigator(
+      key: navigatorKey,
+      pages: [
+        MaterialPage<void>(
+          key: const ValueKey('BooksListPage'),
+          child: BooksListScreen(
+            books: books,
+            onTapped: _handleBookTapped,
+          ),
+        ),
+        if (show404)
+          const MaterialPage<void>(
+            key: ValueKey('UnknownPage'),
+            child: UnknownScreen(),
+          )
+        else if (_selectedBook != null)
+          BookDetailsPage(book: _selectedBook!)
+      ],
+      onPopPage: (route, dynamic result) {
+        if (!route.didPop(result)) {
+          return false;
+        }
+
+        // Update the list of pages by setting _selectedBook to null
+        _selectedBook = null;
+        show404 = false;
+        notifyListeners();
+
+        return true;
+      },
+    );
+  }
+
+  @override
+  Future<void> setNewRoutePath(BookRoutePath configuration) {
+    if (configuration.isUnknown) {
+      _selectedBook = null;
+      show404 = true;
+      return SynchronousFuture<void>(null);
+    }
+
+    if (configuration.isDetailsPage) {
+      if (configuration.id! < 0 || configuration.id! > books.length - 1) {
+        show404 = true;
+        return SynchronousFuture<void>(null);
+      }
+
+      _selectedBook = books[configuration.id!];
+    } else {
+      _selectedBook = null;
+    }
+
+    show404 = false;
+    return SynchronousFuture<void>(null);
+  }
+
+  void _handleBookTapped(Book book) {
+    _selectedBook = book;
+    notifyListeners();
+  }
+}
+
+class BookDetailsPage extends Page<void> {
+  final Book book;
+
+  BookDetailsPage({
+    required this.book,
+  }) : super(key: ValueKey(book));
+
+  @override
+  Route createRoute(BuildContext context) {
+    return MaterialPageRoute<void>(
+      settings: this,
+      builder: (context) {
+        return BookDetailsScreen(book: book);
+      },
+    );
+  }
+}
+
+class BookRoutePath {
+  final int? id;
+  final bool isUnknown;
+
+  BookRoutePath.home()
+      : id = null,
+        isUnknown = false;
+
+  BookRoutePath.details(this.id) : isUnknown = false;
+
+  BookRoutePath.unknown()
+      : id = null,
+        isUnknown = true;
+
+  bool get isHomePage => id == null;
+
+  bool get isDetailsPage => id != null;
+}
+
+class BooksListScreen extends StatelessWidget {
+  final List<Book> books;
+  final ValueChanged<Book> onTapped;
+
+  const BooksListScreen({
+    required this.books,
+    required this.onTapped,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: ListView(
+        children: [
+          for (var book in books)
+            ListTile(
+              title: Text(book.title),
+              subtitle: Text(book.author),
+              onTap: () => onTapped(book),
+            )
+        ],
+      ),
+    );
+  }
+}
+
+class BookDetailsScreen extends StatelessWidget {
+  final Book book;
+
+  const BookDetailsScreen({
+    required this.book,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: Padding(
+        padding: const EdgeInsets.all(8.0),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Text(book.title, style: Theme.of(context).textTheme.headline6),
+            Text(book.author, style: Theme.of(context).textTheme.subtitle1),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+class UnknownScreen extends StatelessWidget {
+  const UnknownScreen({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: const Center(
+        child: Text('404!'),
+      ),
+    );
+  }
+}