update provider demo

更新 provider 到 4.0

新增 selector 的使用样例

mecury_project/example/provider_example/lib/goods_model.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart' show ChangeNotifier;
+
+class GoodsListProvider with ChangeNotifier {
+  List<Goods> _goodsList =
+      List.generate(10, (index) => Goods(false, 'Goods No. $index'));
+
+  get goodsList => _goodsList;
+  get total => _goodsList.length;
+
+  collect(int index) {
+    var good = _goodsList[index];
+    _goodsList[index] = Goods(!good.isCollection, good.goodsName);
+    notifyListeners();
+  }
+}
+
+class Goods {
+  final bool isCollection;
+  final String goodsName;
+
+  Goods(this.isCollection, this.goodsName);
+}

mecury_project/example/provider_example/lib/main.dart

@@ -10,7 +10,7 @@ void main() {
   runApp(
     MultiProvider(providers: [
       Provider<int>(
-        builder: (_) => textSize,
+        create: (_) => textSize,
       ),
       ChangeNotifierProvider<CounterModel>.value(value: counter),
     ], child: MyApp()),
@@ -22,7 +22,27 @@ class MyApp extends StatelessWidget {
   Widget build(BuildContext context) {
     return MaterialApp(
       theme: ThemeData.dark(),
-      home: FirstScreen(),
+      home: DefaultTabController(
+        length: 2,
+        child: Scaffold(
+          appBar: TabBar(tabs: [
+            Tab(
+              text: 'CounterDemo',
+              icon: Icon(Icons.create),
+            ),
+            Tab(
+              text: 'SelectorDemo',
+              icon: Icon(Icons.shopping_cart),
+            ),
+          ]),
+          body: TabBarView(
+            children: [
+              FirstScreen(),
+              GoodsListScreen(),
+            ],
+          ),
+        ),
+      ),
     );
   }
 }

mecury_project/example/provider_example/lib/screens.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import 'counter_model.dart';
 import 'color_model.dart';
+import 'goods_model.dart';
 
 class FirstScreen extends StatelessWidget {
   @override
@@ -145,3 +146,38 @@ class SecondScreen extends StatelessWidget {
     );
   }
 }
+
+class GoodsListScreen extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return ChangeNotifierProvider(
+      create: (_) => GoodsListProvider(),
+      child: Selector<GoodsListProvider, GoodsListProvider>(
+        shouldRebuild: (pre, next) => false,
+        selector: (context, provider) => provider,
+        builder: (context, provider, child) {
+          return ListView.builder(
+            itemCount: provider.total,
+            itemBuilder: (context, index) {
+              return Selector<GoodsListProvider, Goods>(
+                selector: (context, provider) => provider.goodsList[index],
+                builder: (context, data, child) {
+                  print(('No.${index + 1} rebuild'));
+
+                  return ListTile(
+                    title: Text(data.goodsName),
+                    trailing: GestureDetector(
+                      onTap: () => provider.collect(index),
+                      child: Icon(
+                          data.isCollection ? Icons.star : Icons.star_border),
+                    ),
+                  );
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+  }
+}

mecury_project/example/provider_example/pubspec.yaml

@@ -23,7 +23,7 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^0.1.2
-  provider: ^3.0.0+1
+  provider: ^4.0.2
 
 dev_dependencies:
   flutter_test: