Implement ==/hashCode for ViewConfiguration, avoid unnecessary layer creation/replacement (#81928)

packages/flutter/lib/src/rendering/view.dart

@@ -38,6 +38,18 @@ class ViewConfiguration {
     return Matrix4.diagonal3Values(devicePixelRatio, devicePixelRatio, 1.0);
   }
 
+  @override
+  bool operator ==(Object other) {
+    if (other.runtimeType != runtimeType)
+      return false;
+    return other is ViewConfiguration
+        && other.size == size
+        && other.devicePixelRatio == devicePixelRatio;
+  }
+
+  @override
+  int get hashCode => hashValues(size, devicePixelRatio);
+
   @override
   String toString() => '$size at ${debugFormatDouble(devicePixelRatio)}x';
 }

packages/flutter/test/rendering/view_test.dart

@@ -2,12 +2,23 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import 'rendering_tester.dart';
 
 void main() {
+  // Create non-const instances, otherwise tests pass even if the
+  // operator override is incorrect.
+  ViewConfiguration createViewConfiguration({
+    Size size = const Size(20, 20),
+    double devicePixelRatio = 2.0,
+  }) {
+    return ViewConfiguration(size: size, devicePixelRatio: devicePixelRatio);
+  }
+
   group('RenderView', () {
     test('accounts for device pixel ratio in paintBounds', () {
       layout(RenderAspectRatio(aspectRatio: 1.0));
@@ -17,5 +28,33 @@ void main() {
       final Size physicalSize = logicalSize * devicePixelRatio;
       expect(renderer.renderView.paintBounds, Offset.zero & physicalSize);
     });
+
+    test('does not replace the root layer unnecessarily', () {
+      final ui.FlutterView window = TestWindow(window: ui.window);
+      final RenderView view = RenderView(
+        configuration: createViewConfiguration(),
+        window: window,
+      );
+      final PipelineOwner owner = PipelineOwner();
+      view.attach(owner);
+      view.prepareInitialFrame();
+      final ContainerLayer firstLayer = view.debugLayer!;
+      view.configuration = createViewConfiguration();
+      expect(identical(view.debugLayer, firstLayer), true);
+
+      view.configuration = createViewConfiguration(devicePixelRatio: 5.0);
+      expect(identical(view.debugLayer, firstLayer), false);
+    });
+  });
+
+  test('ViewConfiguration == and hashCode', () {
+    final ViewConfiguration viewConfigurationA = createViewConfiguration();
+    final ViewConfiguration viewConfigurationB = createViewConfiguration();
+    final ViewConfiguration viewConfigurationC = createViewConfiguration(devicePixelRatio: 3.0);
+
+    expect(viewConfigurationA == viewConfigurationB, true);
+    expect(viewConfigurationA != viewConfigurationC, true);
+    expect(viewConfigurationA.hashCode, viewConfigurationB.hashCode);
+    expect(viewConfigurationA.hashCode != viewConfigurationC.hashCode, true);
   });
 }