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@chonghorizons
Created December 9, 2021 08:01
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Fixing the Medium writeup linked from Navigator2/Router desciption page. https://medium.com/flutter/learning-flutters-new-navigation-and-routing-system-7c9068155ade
import 'package:flutter/material.dart';
// based on https://medium.com/flutter/learning-flutters-new-navigation-and-routing-system-7c9068155ade
// but update for null safety by Howard "Horizons" Chong, @chonghorizons on github
void main() {
runApp(BooksApp());
}
class Book {
final String title;
final String author;
Book(this.title, this.author);
Book.empty()
: title = '',
author = '';
bool isEmpty() => title == '';
}
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 {
print('BookRouteInformationParser');
print(routeInformation.location);
if (routeInformation.location == null) {
print('Null RouteInformation on startup');
}
final uri = Uri.parse(routeInformation.location ??
'/'); // could be empty, I think it is empty on opp launch
// Handle '/'
if (uri.pathSegments.length == 0) {
return BookRoutePath.home();
}
// Handle '/book/:id'
if (uri.pathSegments.length == 2) {
if (uri.pathSegments[0] != 'book') return BookRoutePath.unknown();
var remaining = uri.pathSegments[1];
var id = int.tryParse(remaining);
if (id == null) return BookRoutePath.unknown();
return BookRoutePath.details(id);
}
// Handle unknown routes
return BookRoutePath.unknown();
}
@override
RouteInformation? restoreRouteInformation(BookRoutePath path) {
print('restoring');
if (path.isUnknown) {
return RouteInformation(location: '/404');
}
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 = Book.empty();
bool show404 = false;
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>();
BookRoutePath get currentConfiguration {
if (show404) {
return BookRoutePath.unknown();
}
return (_selectedBook.isEmpty())
? BookRoutePath.home()
: BookRoutePath.details(books.indexOf(_selectedBook));
}
@override
Widget build(BuildContext context) {
return Navigator(
key: navigatorKey,
pages: [
MaterialPage(
key: ValueKey('BooksListPage'),
child: BooksListScreen(
books: books,
onTapped: _handleBookTapped,
),
),
if (show404)
MaterialPage(key: ValueKey('UnknownPage'), child: UnknownScreen())
else if (!_selectedBook.isEmpty())
BookDetailsPage(book: _selectedBook)
],
onPopPage: (route, result) {
if (!route.didPop(result)) {
return false;
}
// Update the list of pages by setting _selectedBook to empty
_selectedBook = Book.empty();
show404 = false;
notifyListeners();
return true;
},
);
}
@override
Future<void> setNewRoutePath(BookRoutePath path) async {
if (path.isUnknown) {
_selectedBook = Book.empty();
// noBook = true;
show404 = true;
return;
}
if (path.isDetailsPage) {
// if (path.id < 0 || path.id > books.length - 1) {
if (path.id! < 0 || path.id! > books.length - 1) {
show404 = true;
// noBook = true;
return;
}
_selectedBook = books[path.id!];
} else {
_selectedBook = Book.empty();
}
show404 = false;
}
void _handleBookTapped(Book book) {
_selectedBook = book;
// noBook = false;
notifyListeners();
}
}
class BookDetailsPage extends Page {
final Book book;
BookDetailsPage({required 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;
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;
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 UnknownScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Center(
child: Text('404!'),
),
);
}
}
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