Reproduce failure of shouldUpdateModel

example/lib/main_should_update_model_failing.dart

@@ -0,0 +1,145 @@
+import 'package:async_redux/async_redux.dart';
+import 'package:flutter/material.dart';
+
+// Developed by Marcelo Glasberg (Aug 2019).
+// For more info, see: https://pub.dartlang.org/packages/async_redux
+
+late Store<int> store;
+
+/// This example shows how to prevent creating view-models from invalid states.
+/// When the button is tapped, the counter will increment 5 times, synchronously.
+/// So, the sequence would be 0, 5, 10, 15, 20, 25 etc.
+///
+/// However, we consider odd numbers invalid.
+/// Therefore, it will display 0, 4, 10, 14, 20, 24 etc.
+///
+void main() {
+  store = Store<int>(initialState: 0);
+  runApp(MyApp());
+}
+
+class MyApp extends StatefulWidget {
+  @override
+  State<MyApp> createState() => _MyAppState();
+
+  static _MyAppState of(BuildContext context) => context.findAncestorStateOfType<_MyAppState>()!;
+}
+
+class _MyAppState extends State<MyApp> {
+
+  void updateState() => setState(() {});
+
+  @override
+  Widget build(BuildContext context) => StoreProvider<int>(
+      store: store,
+      child: MaterialApp(
+        home: MyHomePageConnector(),
+      ));
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+/// This action increments the counter by [amount]].
+class IncrementAction extends ReduxAction<int> {
+  final int amount;
+
+  IncrementAction({required this.amount});
+
+  @override
+  int reduce() => state + amount;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+class MyHomePageConnector extends StatelessWidget {
+  MyHomePageConnector({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return StoreConnector<int, ViewModel>(
+      vm: () => Factory(this),
+      //
+      // Should update the view-model only when the counter is even.
+      shouldUpdateModel: (int count) => count % 2 == 0,
+      //
+      builder: (BuildContext context, ViewModel vm) => MyHomePage(
+        counter: vm.counter,
+        onIncrement: vm.onIncrement,
+      ),
+    );
+  }
+}
+
+/// Factory that creates a view-model for the StoreConnector.
+class Factory extends VmFactory<int, MyHomePageConnector> {
+  Factory(widget) : super(widget);
+
+  @override
+  ViewModel fromStore() {
+    return ViewModel(
+      counter: state,
+      onIncrement: () {
+        // Increment 5 times.
+        dispatch(IncrementAction(amount: 1));
+        dispatch(IncrementAction(amount: 1));
+        dispatch(IncrementAction(amount: 1));
+        dispatch(IncrementAction(amount: 1));
+        dispatch(IncrementAction(amount: 1));
+      },
+    );
+  }
+}
+
+class ViewModel extends Vm {
+  final int counter;
+  final VoidCallback onIncrement;
+
+  ViewModel({
+    required this.counter,
+    required this.onIncrement,
+  }) : super(equals: [counter]);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+class MyHomePage extends StatelessWidget {
+  final int? counter;
+  final VoidCallback? onIncrement;
+
+  MyHomePage({
+    Key? key,
+    this.counter,
+    this.onIncrement,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('Increment Example')),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            const Padding(
+              padding: const EdgeInsets.all(20.0),
+              child: Text('Each time you push the button it increments 5 times.\n\n'
+                  'But only even values are valid to appear in the UI.\n\n'
+                  'This demonstrates the use of StoreConnector.shouldUpdateModel.'),
+            ),
+            Text('$counter', style: const TextStyle(fontSize: 30)),
+            TextButton(
+              onPressed: () {
+                MyApp.of(context).updateState();
+              },
+              child: const Text('Press after adding pressing add!'),
+            ),
+          ],
+        ),
+      ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: onIncrement,
+        child: const Icon(Icons.add),
+      ),
+    );
+  }
+}