samples/navigation_and_routing/lib/nav_2_advanced/transition_delegate.dart

// 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.

/// Shows how a custom TransitionDelegate can be used to customized when
/// transition animations are shown. (For example, [when two routes are popped
/// off the stack](https://github.com/flutter/flutter/issues/12146), however the
/// default TransitionDelegate will handle this if you are using Navigator 2.0)
import 'package:flutter/material.dart';

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

class Book {
  final String title;
  final String author;

  Book(this.title, this.author);
}

class BooksApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _BooksAppState();
}

class _BooksAppState extends State<BooksApp> {
  BookRouterDelegate _routerDelegate = BookRouterDelegate();
  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) async {
    final uri = Uri.parse(routeInformation.location);

    if (uri.pathSegments.length >= 2) {
      var remaining = uri.pathSegments[1];
      return BookRoutePath.details(int.tryParse(remaining));
    } else {
      return BookRoutePath.home();
    }
  }

  @override
  RouteInformation restoreRouteInformation(BookRoutePath path) {
    if (path.isHomePage) {
      return RouteInformation(location: '/');
    }
    if (path.isDetailsPage) {
      return RouteInformation(location: '/book/${path.id}');
    }
    return null;
  }
}

class BookRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  final GlobalKey<NavigatorState> navigatorKey;

  Book _selectedBook;

  List<Book> books = [
    Book('Stranger in a Strange Land', 'Robert A. Heinlein'),
    Book('Foundation', 'Isaac Asimov'),
    Book('Fahrenheit 451', 'Ray Bradbury'),
  ];

  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>();

  BookRoutePath get currentConfiguration => _selectedBook == null
      ? BookRoutePath.home()
      : BookRoutePath.details(books.indexOf(_selectedBook));

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      transitionDelegate: NoAnimationTransitionDelegate(),
      pages: [
        MaterialPage(
          key: ValueKey('BooksListPage'),
          child: BooksListScreen(
            books: books,
            onTapped: _handleBookTapped,
          ),
        ),
        if (_selectedBook != null) BookDetailsPage(book: _selectedBook)
      ],
      onPopPage: (route, result) {
        if (!route.didPop(result)) {
          return false;
        }

        // Update the list of pages by setting _selectedBook to null
        _selectedBook = null;
        notifyListeners();

        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath path) async {
    if (path.isDetailsPage) {
      _selectedBook = books[path.id];
    }
  }

  void _handleBookTapped(Book book) {
    _selectedBook = book;
    notifyListeners();
  }
}

class BookDetailsPage extends Page {
  final Book book;

  BookDetailsPage({
    this.book,
  }) : super(key: ValueKey(book));

  Route createRoute(BuildContext context) {
    return MaterialPageRoute(
      settings: this,
      builder: (BuildContext context) {
        return BookDetailsScreen(book: book);
      },
    );
  }
}

class BookRoutePath {
  final int id;

  BookRoutePath.home() : id = null;

  BookRoutePath.details(this.id);

  bool get isHomePage => id == null;

  bool get isDetailsPage => id != null;
}

class BooksListScreen extends StatelessWidget {
  final List<Book> books;
  final ValueChanged<Book> onTapped;

  BooksListScreen({
    @required this.books,
    @required this.onTapped,
  });

  @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;

  BookDetailsScreen({
    @required this.book,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            if (book != null) ...[
              Text(book.title, style: Theme.of(context).textTheme.headline6),
              Text(book.author, style: Theme.of(context).textTheme.subtitle1),
            ],
          ],
        ),
      ),
    );
  }
}

class NoAnimationTransitionDelegate extends TransitionDelegate<void> {
  @override
  Iterable<RouteTransitionRecord> resolve({
    List<RouteTransitionRecord> newPageRouteHistory,
    Map<RouteTransitionRecord, RouteTransitionRecord>
    locationToExitingPageRoute,
    Map<RouteTransitionRecord, List<RouteTransitionRecord>>
    pageRouteToPagelessRoutes,
  }) {
    final results = <RouteTransitionRecord>[];

    for (final pageRoute in newPageRouteHistory) {
      if (pageRoute.isWaitingForEnteringDecision) {
        pageRoute.markForAdd();
      }
      results.add(pageRoute);
    }

    for (final exitingPageRoute in locationToExitingPageRoute.values) {
      if (exitingPageRoute.isWaitingForExitingDecision) {
        exitingPageRoute.markForRemove();
        final pagelessRoutes = pageRouteToPagelessRoutes[exitingPageRoute];
        if (pagelessRoutes != null) {
          for (final pagelessRoute in pagelessRoutes) {
            pagelessRoute.markForRemove();
          }
        }
      }

      results.add(exitingPageRoute);
    }
    return results;
  }
}