Add counter and notifier for a value.

lib/mains/gt.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
+import 'package:riverpod_flutter_tuts/widgets/notifier/counter_widget.dart';
 
 import '../widgets/consumer/random.dart';
 import '../widgets/simples/random.dart';
@@ -42,7 +43,8 @@ class MyApp extends ConsumerWidget {
               const Expanded(child: Text('1')),
               Expanded(child: Text(value)),
               const Expanded(child: RandomWidget()),
-              const Expanded(child: Random2Widget())
+              const Expanded(child: Random2Widget()),
+              const Expanded(child: CounterWidget()),
             ],
           )
 

lib/widgets/notifier/counter.dart

@@ -0,0 +1,29 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+
+part 'counter.g.dart';
+
+@riverpod
+class CounterNotifier extends _$CounterNotifier {
+
+  int x = 0;
+  @override
+  Future<int> build()  async{
+    return x;
+  }
+
+  void plus() {
+    x++;
+    ref.invalidateSelf();
+    // state = AsyncData(x);
+  }
+
+  void minus() {
+    x--;
+    // ref.invalidateSelf();
+    state = AsyncData(x);
+  }
+}

lib/widgets/notifier/counter_widget.dart

@@ -0,0 +1,34 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:riverpod_flutter_tuts/widgets/notifier/counter.dart';
+
+
+class CounterWidget extends ConsumerWidget {
+  const CounterWidget({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    // TODO: implement build
+
+    var myRandom = ref.watch(counterNotifierProvider);
+    return Column(
+      children: [
+        Center(
+        child: switch (myRandom) {
+      AsyncData(:final value ) => Text(
+          'data: $value'
+      ),
+    AsyncError() => const Text('Oops, something unexpected happened'),
+    _ => const CircularProgressIndicator(),
+    }),
+        ElevatedButton(onPressed:() {
+          ref.read(counterNotifierProvider.notifier).plus();
+        }, child: const Text("plus")),
+        ElevatedButton(onPressed: () {
+        ref.read(counterNotifierProvider.notifier).minus();
+        }, child: const Text("minus")),
+    ]
+    );
+  }
+}