navigation_and_routing: a bunch of cleanup (#886)

Fail early on nullable context objects - no code paths allow null
Eliminate superfluous private function
Use a function over an abstract class with one method

navigation_and_routing/lib/src/app.dart

@@ -48,8 +48,6 @@ class _BookstoreState extends State<Bookstore> {
 
   @override
   void initState() {
-    final guard = BookstoreRouteGuard(auth: _auth);
-
     /// Configure the parser with all of the app's allowed path templates.
     _routeParser = TemplateRouteParser(
       allowedPaths: [
@@ -62,7 +60,7 @@ class _BookstoreState extends State<Bookstore> {
         '/book/:bookId',
         '/author/:authorId',
       ],
-      guard: guard,
+      guard: _guard,
       initialRoute: '/signin',
     );
 
@@ -97,6 +95,21 @@ class _BookstoreState extends State<Bookstore> {
         ),
       );
 
+  Future<ParsedRoute> _guard(ParsedRoute from) async {
+    final signedIn = _auth.signedIn;
+    final signInRoute = ParsedRoute('/signin', '/signin', {}, {});
+
+    // Go to /signin if the user is not signed in
+    if (!signedIn && from != signInRoute) {
+      return signInRoute;
+    }
+    // Go to /books if the user is signed in and tries to go to /signin.
+    else if (signedIn && from == signInRoute) {
+      return ParsedRoute('/books/popular', '/books/popular', {}, {});
+    }
+    return from;
+  }
+
   void _handleAuthStateChanged() {
     if (!_auth.signedIn) {
       _routeState.go('/signin');

navigation_and_routing/lib/src/auth.dart

@@ -2,5 +2,47 @@
 // 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.
 
-export 'auth/auth.dart';
-export 'auth/auth_guard.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+/// A mock authentication service
+class BookstoreAuth extends ChangeNotifier {
+  bool _signedIn = false;
+
+  bool get signedIn => _signedIn;
+
+  Future<void> signOut() async {
+    await Future<void>.delayed(const Duration(milliseconds: 200));
+    // Sign out.
+    _signedIn = false;
+    notifyListeners();
+  }
+
+  Future<bool> signIn(String username, String password) async {
+    await Future<void>.delayed(const Duration(milliseconds: 200));
+
+    // Sign in. Allow any password.
+    _signedIn = true;
+    notifyListeners();
+    return _signedIn;
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is BookstoreAuth && other._signedIn == _signedIn;
+
+  @override
+  int get hashCode => _signedIn.hashCode;
+}
+
+class BookstoreAuthScope extends InheritedNotifier<BookstoreAuth> {
+  const BookstoreAuthScope({
+    required BookstoreAuth notifier,
+    required Widget child,
+    Key? key,
+  }) : super(key: key, notifier: notifier, child: child);
+
+  static BookstoreAuth of(BuildContext context) => context
+      .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()!
+      .notifier!;
+}

navigation_and_routing/lib/src/auth/auth.dart

@@ -1,48 +0,0 @@
-// Copyright 2021, 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.
-
-import 'package:flutter/foundation.dart';
-import 'package:flutter/widgets.dart';
-
-/// A mock authentication service
-class BookstoreAuth extends ChangeNotifier {
-  bool _signedIn = false;
-
-  bool get signedIn => _signedIn;
-
-  Future<void> signOut() async {
-    await Future<void>.delayed(const Duration(milliseconds: 200));
-    // Sign out.
-    _signedIn = false;
-    notifyListeners();
-  }
-
-  Future<bool> signIn(String username, String password) async {
-    await Future<void>.delayed(const Duration(milliseconds: 200));
-
-    // Sign in. Allow any password.
-    _signedIn = true;
-    notifyListeners();
-    return _signedIn;
-  }
-
-  @override
-  bool operator ==(Object other) =>
-      other is BookstoreAuth && other._signedIn == _signedIn;
-
-  @override
-  int get hashCode => _signedIn.hashCode;
-}
-
-class BookstoreAuthScope extends InheritedNotifier<BookstoreAuth> {
-  const BookstoreAuthScope({
-    required BookstoreAuth notifier,
-    required Widget child,
-    Key? key,
-  }) : super(key: key, notifier: notifier, child: child);
-
-  static BookstoreAuth? of(BuildContext context) => context
-      .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()
-      ?.notifier;
-}

navigation_and_routing/lib/src/auth/auth_guard.dart

@@ -1,32 +0,0 @@
-// Copyright 2021, 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.
-
-import '../routing.dart';
-import 'auth.dart';
-
-/// An implementation of [RouteGuard] that redirects to /signIn
-class BookstoreRouteGuard implements RouteGuard<ParsedRoute> {
-  final BookstoreAuth auth;
-
-  BookstoreRouteGuard({
-    required this.auth,
-  });
-
-  /// Redirect to /signin if the user isn't signed in.
-  @override
-  Future<ParsedRoute> redirect(ParsedRoute from) async {
-    final signedIn = auth.signedIn;
-    final signInRoute = ParsedRoute('/signin', '/signin', {}, {});
-
-    // Go to /signin if the user is not signed in
-    if (!signedIn && from != signInRoute) {
-      return signInRoute;
-    }
-    // Go to /books if the user is signed in and tries to go to /signin.
-    else if (signedIn && from == signInRoute) {
-      return ParsedRoute('/books/popular', '/books/popular', {}, {});
-    }
-    return from;
-  }
-}

navigation_and_routing/lib/src/routing/parser.dart

@@ -8,18 +8,12 @@ import 'package:path_to_regexp/path_to_regexp.dart';
 import 'parsed_route.dart';
 
 /// Used by [TemplateRouteParser] to guard access to routes.
-///
-/// Override this class to change the route that is returned by
-/// [TemplateRouteParser.parseRouteInformation] if a condition is not met, for
-/// example, if the user is not signed in.
-abstract class RouteGuard<T> {
-  Future<T> redirect(T from);
-}
+typedef RouteGuard<T> = Future<T> Function(T from);
 
 /// Parses the URI path into a [ParsedRoute].
 class TemplateRouteParser extends RouteInformationParser<ParsedRoute> {
-  final List<String> _pathTemplates = [];
-  RouteGuard<ParsedRoute>? guard;
+  final List<String> _pathTemplates;
+  final RouteGuard<ParsedRoute>? guard;
   final ParsedRoute initialRoute;
 
   TemplateRouteParser({
@@ -27,27 +21,20 @@ class TemplateRouteParser extends RouteInformationParser<ParsedRoute> {
     required List<String> allowedPaths,
 
     /// The initial route
-    String? initialRoute = '/',
+    String initialRoute = '/',
 
     ///  [RouteGuard] used to redirect.
     this.guard,
-  }) : initialRoute =
-            ParsedRoute(initialRoute ?? '/', initialRoute ?? '/', {}, {}) {
-    for (var template in allowedPaths) {
-      _addRoute(template);
-    }
-  }
-
-  void _addRoute(String pathTemplate) {
-    _pathTemplates.add(pathTemplate);
-  }
+  })  : initialRoute = ParsedRoute(initialRoute, initialRoute, {}, {}),
+        _pathTemplates = [
+          ...allowedPaths,
+        ],
+        assert(allowedPaths.contains(initialRoute));
 
   @override
   Future<ParsedRoute> parseRouteInformation(
-          RouteInformation routeInformation) async =>
-      await _parse(routeInformation);
-
-  Future<ParsedRoute> _parse(RouteInformation routeInformation) async {
+    RouteInformation routeInformation,
+  ) async {
     final path = routeInformation.location!;
     final queryParams = Uri.parse(path).queryParameters;
     var parsedRoute = initialRoute;
@@ -66,7 +53,7 @@ class TemplateRouteParser extends RouteInformationParser<ParsedRoute> {
     // Redirect if a guard is present
     var guard = this.guard;
     if (guard != null) {
-      return guard.redirect(parsedRoute);
+      return guard(parsedRoute);
     }
 
     return parsedRoute;

navigation_and_routing/lib/src/routing/route_state.dart

@@ -44,6 +44,6 @@ class RouteStateScope extends InheritedNotifier<RouteState> {
     Key? key,
   }) : super(key: key, notifier: notifier, child: child);
 
-  static RouteState? of(BuildContext context) =>
-      context.dependOnInheritedWidgetOfExactType<RouteStateScope>()?.notifier;
+  static RouteState of(BuildContext context) =>
+      context.dependOnInheritedWidgetOfExactType<RouteStateScope>()!.notifier!;
 }

navigation_and_routing/lib/src/screens/author_details.dart

@@ -28,7 +28,7 @@ class AuthorDetailsScreen extends StatelessWidget {
                 child: BookList(
                   books: author.books,
                   onTap: (book) {
-                    RouteStateScope.of(context)!.go('/book/${book.id}');
+                    RouteStateScope.of(context).go('/book/${book.id}');
                   },
                 ),
               ),

navigation_and_routing/lib/src/screens/authors.dart

@@ -21,7 +21,7 @@ class AuthorsScreen extends StatelessWidget {
         body: AuthorList(
           authors: LibraryScope.of(context).allAuthors,
           onTap: (author) {
-            RouteStateScope.of(context)!.go('/author/${author.id}');
+            RouteStateScope.of(context).go('/author/${author.id}');
           },
         ),
       );

navigation_and_routing/lib/src/screens/books.dart

@@ -93,7 +93,7 @@ class _BooksScreenState extends State<BooksScreen>
     );
   }
 
-  RouteState get _routeState => RouteStateScope.of(context)!;
+  RouteState get _routeState => RouteStateScope.of(context);
 
   void _handleBookTapped(Book book) {
     _routeState.go('/book/${book.id}');

navigation_and_routing/lib/src/screens/navigator.dart

@@ -37,8 +37,8 @@ class _BookstoreNavigatorState extends State<BookstoreNavigator> {
 
   @override
   Widget build(BuildContext context) {
-    final routeState = RouteStateScope.of(context)!;
-    final authState = BookstoreAuthScope.of(context)!;
+    final routeState = RouteStateScope.of(context);
+    final authState = BookstoreAuthScope.of(context);
     final pathTemplate = routeState.route.pathTemplate;
     final library = LibraryScope.of(context);
 

navigation_and_routing/lib/src/screens/scaffold.dart

@@ -15,7 +15,7 @@ class BookstoreScaffold extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final routeState = RouteStateScope.of(context)!;
+    final routeState = RouteStateScope.of(context);
     final selectedIndex = _getSelectedIndex(routeState.route.pathTemplate);
 
     return Scaffold(

navigation_and_routing/lib/src/screens/scaffold_body.dart

@@ -21,7 +21,7 @@ class BookstoreScaffoldBody extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    var currentRoute = RouteStateScope.of(context)!.route;
+    var currentRoute = RouteStateScope.of(context).route;
 
     // A nested Router isn't necessary because the back button behavior doesn't
     // need to be customized.

navigation_and_routing/lib/src/screens/settings.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 import 'package:url_launcher/link.dart';
 
-import '../auth/auth.dart';
+import '../auth.dart';
 import '../routing.dart';
 
 class SettingsScreen extends StatefulWidget {
@@ -52,7 +52,7 @@ class SettingsContent extends StatelessWidget {
             ),
             ElevatedButton(
               onPressed: () {
-                BookstoreAuthScope.of(context)!.signOut();
+                BookstoreAuthScope.of(context).signOut();
               },
               child: const Text('Sign out'),
             ),
@@ -66,7 +66,7 @@ class SettingsContent extends StatelessWidget {
             TextButton(
               child: const Text('Go directly to /book/0 (RouteState)'),
               onPressed: () {
-                RouteStateScope.of(context)!.go('/book/0');
+                RouteStateScope.of(context).go('/book/0');
               },
             ),
           ].map((w) => Padding(padding: const EdgeInsets.all(8), child: w)),