Create flutter_provider.dart

dart/flutter_provider.dart

@@ -0,0 +1,105 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+// This is a reimplementation of the default Flutter application
+// using provider + [ChangeNotifier].
+void main() {
+  runApp(
+    // Providers are above [MyApp] instead of inside it, so that
+    // tests can use [MyApp] while mocking the providers
+    MultiProvider(
+      providers: [
+        ChangeNotifierProvider(create: (context) => Counter()),
+      ],
+      child: const MyApp(),
+    ),
+  );
+}
+
+// Mix-in [DiagnosticableTreeMixin] to have access to
+// [debugFillProperties] for the devtool ignore: prefer_mixin
+class Counter with ChangeNotifier, DiagnosticableTreeMixin {
+  int _count = 0;
+
+  int get count => _count;
+
+  void increment() {
+    _count++;
+    notifyListeners();
+  }
+
+  // Makes `Counter` readable inside the devtools by listing all
+  // of its properties.
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(IntProperty('count', count));
+  }
+}
+
+class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      home: MyHomePage(),
+    );
+  }
+}
+
+class MyHomePage extends StatelessWidget {
+  const MyHomePage({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Provider example'),
+      ),
+      body: Center(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: const <Widget>[
+            Text('You have pushed the button this many times:'),
+
+            // Extracted as a separate widget for performance
+            // optimization. As a separate widget, it will rebuild
+            // independently from [MyHomePage].
+            //
+            // This is totally optional (and rarely needed).
+            // Similarly, we could also use [Consumer] or
+            // [Selector].
+            Count(),
+          ],
+        ),
+      ),
+      floatingActionButton: FloatingActionButton(
+        key: const Key('increment_floatingActionButton'),
+
+        // Calls `context.read` instead of `context.watch` so
+        // that it does not rebuild when [Counter] changes.
+        onPressed: () => context.read<Counter>().increment(),
+        tooltip: 'Increment',
+        child: const Icon(Icons.add),
+      ),
+    );
+  }
+}
+
+class Count extends StatelessWidget {
+  const Count({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Text(
+      // Calls `context.watch` to make [Count] rebuild when
+      // [Counter] changes.
+      '${context.watch<Counter>().count}',
+      key: const Key('counterState'),
+      style: Theme.of(context).textTheme.headline4,
+    );
+  }
+}