From 69882d9647e03ec4a9189ee1b0351abae508e938 Mon Sep 17 00:00:00 2001
From: Bogdan Lukin <lukin.bogdan.a@gmail.com>
Date: Thu, 4 Feb 2021 06:06:05 +0700
Subject: [PATCH] Fix/ValueListenableBuilder rebuilds (#72707)

---
 .../src/widgets/value_listenable_builder.dart |  4 +-
 .../value_listenable_builder_test.dart        | 44 +++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/packages/flutter/lib/src/widgets/value_listenable_builder.dart b/packages/flutter/lib/src/widgets/value_listenable_builder.dart
index 1d9d32db9d8..d3b99e945d2 100644
--- a/packages/flutter/lib/src/widgets/value_listenable_builder.dart
+++ b/packages/flutter/lib/src/widgets/value_listenable_builder.dart
@@ -179,7 +179,9 @@ class _ValueListenableBuilderState<T> extends State<ValueListenableBuilder<T>> {
   }
 
   void _valueChanged() {
-    setState(() { value = widget.valueListenable.value; });
+    if (value != widget.valueListenable.value) {
+      setState(() { value = widget.valueListenable.value; });
+    }
   }
 
   @override
diff --git a/packages/flutter/test/widgets/value_listenable_builder_test.dart b/packages/flutter/test/widgets/value_listenable_builder_test.dart
index e90658a57c8..f3b9d53a0df 100644
--- a/packages/flutter/test/widgets/value_listenable_builder_test.dart
+++ b/packages/flutter/test/widgets/value_listenable_builder_test.dart
@@ -9,6 +9,7 @@ import 'package:flutter/widgets.dart';
 void main() {
   late SpyStringValueNotifier valueListenable;
   late Widget textBuilderUnderTest;
+  late int rebuildCount;
 
   Widget builderForValueListenable(
     ValueListenable<String?> valueListenable,
@@ -18,6 +19,8 @@ void main() {
       child: ValueListenableBuilder<String?>(
         valueListenable: valueListenable,
         builder: (BuildContext context, String? value, Widget? child) {
+          rebuildCount += 1;
+
           if (value == null)
             return const Placeholder();
           return Text(value);
@@ -29,6 +32,7 @@ void main() {
   setUp(() {
     valueListenable = SpyStringValueNotifier(null);
     textBuilderUnderTest = builderForValueListenable(valueListenable);
+    rebuildCount = 0;
   });
 
   testWidgets('Null value is ok', (WidgetTester tester) async {
@@ -58,6 +62,46 @@ void main() {
     expect(find.text('Dinesh'), findsOneWidget);
   });
 
+  testWidgets('Widget does not rebuilds if value is the same', (WidgetTester tester) async {
+    const Duration duration = Duration(milliseconds: 100);
+    final AnimationController controller = AnimationController(
+      vsync: const TestVSync(),
+      duration: duration,
+    )..value = 0;
+    final Animation<String> animation = TweenSequence<String>(<TweenSequenceItem<String>>[
+      TweenSequenceItem<String>(tween: ConstantTween<String>('Gilfoyle'), weight: 1.0),
+      TweenSequenceItem<String>(tween: ConstantTween<String>('Dinesh'), weight: 1.0),
+    ]).animate(controller);
+
+    final Finder finder1 = find.text('Gilfoyle');
+    final Finder finder2 = find.text('Dinesh');
+
+    await tester.pumpWidget(builderForValueListenable(animation));
+
+    await tester.pump();
+    expect(finder1, findsOneWidget);
+    expect(finder2, findsNothing);
+    expect(rebuildCount, equals(1));
+
+    controller.value = 0.3;
+    await tester.pump();
+    expect(finder1, findsOneWidget);
+    expect(finder2, findsNothing);
+    expect(rebuildCount, equals(1));
+
+    controller.animateTo(0.6);
+    await tester.pumpAndSettle(duration);
+    expect(finder1, findsNothing);
+    expect(finder2, findsOneWidget);
+    expect(rebuildCount, equals(2));
+
+    controller.forward();
+    await tester.pumpAndSettle(duration);
+    expect(finder1, findsNothing);
+    expect(finder2, findsOneWidget);
+    expect(rebuildCount, equals(2));
+  });
+
   testWidgets('Can change listenable', (WidgetTester tester) async {
     await tester.pumpWidget(textBuilderUnderTest);