[place_tracker] ChangeNotifierProvider for state management (#424)

place_tracker/lib/app_model.dart

@@ -1,67 +0,0 @@
-import 'package:flutter/material.dart';
-
-class _AppModelScope<T> extends InheritedWidget {
-  const _AppModelScope({
-    Key key,
-    this.appModelState,
-    Widget child,
-  }) : super(key: key, child: child);
-
-  final _AppModelState<T> appModelState;
-
-  @override
-  bool updateShouldNotify(_AppModelScope oldWidget) => true;
-}
-
-class AppModel<T> extends StatefulWidget {
-  AppModel({
-    Key key,
-    @required this.initialState,
-    this.child,
-  })  : assert(initialState != null),
-        super(key: key);
-
-  final T initialState;
-  final Widget child;
-
-  @override
-  _AppModelState<T> createState() => _AppModelState<T>();
-
-  static T of<T>(BuildContext context) {
-    final scope =
-        context.dependOnInheritedWidgetOfExactType<_AppModelScope<T>>();
-    return scope.appModelState.currentState;
-  }
-
-  static void update<T>(BuildContext context, T newState) {
-    final scope =
-        context.dependOnInheritedWidgetOfExactType<_AppModelScope<T>>();
-    scope.appModelState.updateState(newState);
-  }
-}
-
-class _AppModelState<T> extends State<AppModel<T>> {
-  @override
-  void initState() {
-    super.initState();
-    currentState = widget.initialState;
-  }
-
-  T currentState;
-
-  void updateState(T newState) {
-    if (newState != currentState) {
-      setState(() {
-        currentState = newState;
-      });
-    }
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return _AppModelScope<T>(
-      appModelState: this,
-      child: widget.child,
-    );
-  }
-}

place_tracker/lib/main.dart

@@ -1,7 +1,11 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 
 import 'place_tracker_app.dart';
 
 void main() {
-  runApp(PlaceTrackerApp());
+  runApp(ChangeNotifierProvider(
+    create: (context) => AppState(),
+    child: PlaceTrackerApp(),
+  ));
 }

place_tracker/lib/place.dart

@@ -29,6 +29,7 @@ class Place {
   final int starRating;
 
   double get latitude => latLng.latitude;
+
   double get longitude => latLng.longitude;
 
   Place copyWith({

place_tracker/lib/place_list.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 
 import 'place.dart';
 import 'place_details.dart';
@@ -16,24 +17,27 @@ class PlaceListState extends State<PlaceList> {
 
   void _onCategoryChanged(PlaceCategory newCategory) {
     _scrollController.jumpTo(0.0);
-    AppState.updateWith(context, selectedCategory: newCategory);
+    Provider.of<AppState>(context, listen: false)
+        .setSelectedCategory(newCategory);
   }
 
   void _onPlaceChanged(Place value) {
     // Replace the place with the modified version.
-    final newPlaces = List<Place>.from(AppState.of(context).places);
+    final newPlaces =
+        List<Place>.from(Provider.of<AppState>(context, listen: false).places);
     final index = newPlaces.indexWhere((place) => place.id == value.id);
     newPlaces[index] = value;
 
-    AppState.updateWith(context, places: newPlaces);
+    Provider.of<AppState>(context, listen: false).setPlaces(newPlaces);
   }
 
   @override
   Widget build(BuildContext context) {
+    var state = Provider.of<AppState>(context);
     return Column(
       children: <Widget>[
         _ListCategoryButtonBar(
-          selectedCategory: AppState.of(context).selectedCategory,
+          selectedCategory: state.selectedCategory,
           onCategoryChanged: (value) => _onCategoryChanged(value),
         ),
         Expanded(
@@ -41,10 +45,8 @@ class PlaceListState extends State<PlaceList> {
             padding: const EdgeInsets.fromLTRB(16.0, 0.0, 16.0, 8.0),
             controller: _scrollController,
             shrinkWrap: true,
-            children: AppState.of(context)
+            children: state.places
-                .places
+                .where((place) => place.category == state.selectedCategory)
-                .where((place) =>
-                    place.category == AppState.of(context).selectedCategory)
                 .map((place) => _PlaceListTile(
                       place: place,
                       onPlaceChanged: (value) => _onPlaceChanged(value),

place_tracker/lib/place_map.dart

@@ -1,8 +1,10 @@
 import 'dart:async';
 import 'dart:math';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';
+import 'package:provider/provider.dart';
 import 'package:uuid/uuid.dart';
 
 import 'place.dart';
@@ -65,7 +67,7 @@ class PlaceMapState extends State<PlaceMap> {
     // Draw initial place markers on creation so that we have something
     // interesting to look at.
     var markers = <Marker>{};
-    for (var place in AppState.of(context).places) {
+    for (var place in Provider.of<AppState>(context, listen: false).places) {
       markers.add(await _createPlaceMarker(context, place));
     }
     setState(() {
@@ -75,7 +77,7 @@ class PlaceMapState extends State<PlaceMap> {
     // Zoom to fit the initially selected category.
     await _zoomToFitPlaces(
       _getPlacesForCategory(
-        AppState.of(context).selectedCategory,
+        Provider.of<AppState>(context, listen: false).selectedCategory,
         _markedPlaces.values.toList(),
       ),
     );
@@ -91,7 +93,8 @@ class PlaceMapState extends State<PlaceMap> {
         onTap: () => _pushPlaceDetailsScreen(place),
       ),
       icon: await _getPlaceMarkerIcon(context, place.category),
-      visible: place.category == AppState.of(context).selectedCategory,
+      visible: place.category ==
+          Provider.of<AppState>(context, listen: false).selectedCategory,
     );
     _markedPlaces[marker] = place;
     return marker;
@@ -113,7 +116,8 @@ class PlaceMapState extends State<PlaceMap> {
 
   void _onPlaceChanged(Place value) {
     // Replace the place with the modified version.
-    final newPlaces = List<Place>.from(AppState.of(context).places);
+    final newPlaces =
+        List<Place>.from(Provider.of<AppState>(context, listen: false).places);
     final index = newPlaces.indexWhere((place) => place.id == value.id);
     newPlaces[index] = value;
 
@@ -124,10 +128,11 @@ class PlaceMapState extends State<PlaceMap> {
     // in the main build method due to a modified AppState.
     _configuration = MapConfiguration(
       places: newPlaces,
-      selectedCategory: AppState.of(context).selectedCategory,
+      selectedCategory:
+          Provider.of<AppState>(context, listen: false).selectedCategory,
     );
 
-    AppState.updateWith(context, places: newPlaces);
+    Provider.of<AppState>(context, listen: false).setPlaces(newPlaces);
   }
 
   void _updateExistingPlaceMarker({@required Place place}) {
@@ -159,7 +164,7 @@ class PlaceMapState extends State<PlaceMap> {
   }
 
   Future<void> _switchSelectedCategory(PlaceCategory category) async {
-    AppState.updateWith(context, selectedCategory: category);
+    Provider.of<AppState>(context, listen: false).setSelectedCategory(category);
     await _showPlacesForSelectedCategory(category);
   }
 
@@ -233,11 +238,12 @@ class PlaceMapState extends State<PlaceMap> {
         id: Uuid().v1(),
         latLng: _pendingMarker.position,
         name: _pendingMarker.infoWindow.title,
-        category: AppState.of(context).selectedCategory,
+        category:
+            Provider.of<AppState>(context, listen: false).selectedCategory,
       );
 
-      var placeMarker = await _getPlaceMarkerIcon(
+      var placeMarker = await _getPlaceMarkerIcon(context,
-          context, AppState.of(context).selectedCategory);
+          Provider.of<AppState>(context, listen: false).selectedCategory);
 
       setState(() {
         final updatedMarker = _pendingMarker.copyWith(
@@ -275,18 +281,20 @@ class PlaceMapState extends State<PlaceMap> {
       );
 
       // Add the new place to the places stored in appState.
-      final newPlaces = List<Place>.from(AppState.of(context).places)
+      final newPlaces =
-        ..add(newPlace);
+          List<Place>.from(Provider.of<AppState>(context, listen: false).places)
+            ..add(newPlace);
 
       // Manually update our map configuration here since our map is already
       // updated with the new marker. Otherwise, the map would be reconfigured
       // in the main build method due to a modified AppState.
       _configuration = MapConfiguration(
         places: newPlaces,
-        selectedCategory: AppState.of(context).selectedCategory,
+        selectedCategory:
+            Provider.of<AppState>(context, listen: false).selectedCategory,
       );
 
-      AppState.updateWith(context, places: newPlaces);
+      Provider.of<AppState>(context, listen: false).setPlaces(newPlaces);
     }
   }
 
@@ -309,8 +317,10 @@ class PlaceMapState extends State<PlaceMap> {
   }
 
   Future<void> _maybeUpdateMapConfiguration() async {
-    _configuration ??= MapConfiguration.of(AppState.of(context));
+    _configuration ??=
-    final newConfiguration = MapConfiguration.of(AppState.of(context));
+        MapConfiguration.of(Provider.of<AppState>(context, listen: false));
+    final newConfiguration =
+        MapConfiguration.of(Provider.of<AppState>(context, listen: false));
 
     // Since we manually update [_configuration] when place or selectedCategory
     // changes come from the [place_map], we should only enter this if statement
@@ -344,6 +354,7 @@ class PlaceMapState extends State<PlaceMap> {
   @override
   Widget build(BuildContext context) {
     _maybeUpdateMapConfiguration();
+    var state = Provider.of<AppState>(context);
 
     return Builder(builder: (context) {
       // We need this additional builder here so that we can pass its context to
@@ -364,7 +375,7 @@ class PlaceMapState extends State<PlaceMap> {
               onCameraMove: (position) => _lastMapPosition = position.target,
             ),
             _CategoryButtonBar(
-              selectedPlaceCategory: AppState.of(context).selectedCategory,
+              selectedPlaceCategory: state.selectedCategory,
               visible: _pendingMarker == null,
               onChanged: _switchSelectedCategory,
             ),

place_tracker/lib/place_tracker_app.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';
+import 'package:provider/provider.dart';
 
-import 'app_model.dart';
 import 'place.dart';
 import 'place_list.dart';
 import 'place_map.dart';
@@ -12,23 +12,10 @@ enum PlaceTrackerViewType {
   list,
 }
 
-class PlaceTrackerApp extends StatefulWidget {
+class PlaceTrackerApp extends StatelessWidget {
-  @override
-  _PlaceTrackerAppState createState() => _PlaceTrackerAppState();
-}
-
-class _PlaceTrackerAppState extends State<PlaceTrackerApp> {
-  AppState appState = AppState();
-
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
-      builder: (context, child) {
-        return AppModel<AppState>(
-          initialState: AppState(),
-          child: child,
-        );
-      },
       home: _PlaceTrackerHomePage(),
     );
   }
@@ -39,6 +26,7 @@ class _PlaceTrackerHomePage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    var state = Provider.of<AppState>(context);
     return Scaffold(
       appBar: AppBar(
         title: Row(
@@ -57,18 +45,16 @@ class _PlaceTrackerHomePage extends StatelessWidget {
             padding: EdgeInsets.fromLTRB(0.0, 0.0, 16.0, 0.0),
             child: IconButton(
               icon: Icon(
-                AppState.of(context).viewType == PlaceTrackerViewType.map
+                state.viewType == PlaceTrackerViewType.map
                     ? Icons.list
                     : Icons.map,
                 size: 32.0,
               ),
               onPressed: () {
-                AppState.updateWith(
+                state.setViewType(
-                  context,
+                  state.viewType == PlaceTrackerViewType.map
-                  viewType:
+                      ? PlaceTrackerViewType.list
-                      AppState.of(context).viewType == PlaceTrackerViewType.map
+                      : PlaceTrackerViewType.map,
-                          ? PlaceTrackerViewType.list
-                          : PlaceTrackerViewType.map,
                 );
               },
             ),
@@ -76,61 +62,41 @@ class _PlaceTrackerHomePage extends StatelessWidget {
         ],
       ),
       body: IndexedStack(
-        index:
+        index: state.viewType == PlaceTrackerViewType.map ? 0 : 1,
-            AppState.of(context).viewType == PlaceTrackerViewType.map ? 0 : 1,
         children: <Widget>[
           PlaceMap(center: const LatLng(45.521563, -122.677433)),
-          PlaceList(),
+          PlaceList()
         ],
       ),
     );
   }
 }
 
-class AppState {
+class AppState extends ChangeNotifier {
-  const AppState({
+  AppState({
     this.places = StubData.places,
     this.selectedCategory = PlaceCategory.favorite,
     this.viewType = PlaceTrackerViewType.map,
   })  : assert(places != null),
         assert(selectedCategory != null);
 
-  final List<Place> places;
+  List<Place> places;
-  final PlaceCategory selectedCategory;
+  PlaceCategory selectedCategory;
-  final PlaceTrackerViewType viewType;
+  PlaceTrackerViewType viewType;
 
-  AppState copyWith({
+  void setViewType(PlaceTrackerViewType viewType) {
-    List<Place> places,
+    this.viewType = viewType;
-    PlaceCategory selectedCategory,
+    notifyListeners();
-    PlaceTrackerViewType viewType,
-  }) {
-    return AppState(
-      places: places ?? this.places,
-      selectedCategory: selectedCategory ?? this.selectedCategory,
-      viewType: viewType ?? this.viewType,
-    );
   }
 
-  static AppState of(BuildContext context) => AppModel.of<AppState>(context);
+  void setSelectedCategory(PlaceCategory newCategory) {
-
+    selectedCategory = newCategory;
-  static void update(BuildContext context, AppState newState) {
+    notifyListeners();
-    AppModel.update<AppState>(context, newState);
   }
 
-  static void updateWith(
+  void setPlaces(List<Place> newPlaces) {
-    BuildContext context, {
+    places = newPlaces;
-    List<Place> places,
+    notifyListeners();
-    PlaceCategory selectedCategory,
-    PlaceTrackerViewType viewType,
-  }) {
-    update(
-      context,
-      AppState.of(context).copyWith(
-        places: places,
-        selectedCategory: selectedCategory,
-        viewType: viewType,
-      ),
-    );
   }
 
   @override

place_tracker/pubspec.lock

@@ -116,6 +116,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.8"
+  nested:
+    dependency: transitive
+    description:
+      name: nested
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.0.4"
   path:
     dependency: transitive
     description:
@@ -144,6 +151,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.0.2"
+  provider:
+    dependency: "direct dev"
+    description:
+      name: provider
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "4.0.5+1"
   quiver:
     dependency: transitive
     description:

place_tracker/pubspec.yaml

@@ -18,6 +18,7 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   pedantic: ^1.9.0
+  provider: ^4.0.5+1
 
 flutter:
   assets: