Fix leaks (#126144)

Fixes https://github.com/flutter/flutter/issues/126096.
Fixes https://github.com/flutter/flutter/issues/126097.
Fixes https://github.com/flutter/flutter/issues/126102.
Fixes https://github.com/flutter/flutter/issues/126098.
Fixes https://github.com/flutter/flutter/issues/126147.
Work towards https://github.com/flutter/flutter/issues/126100.

Does not fix the OverlyEntry/ModalRoute leak (https://github.com/flutter/flutter/issues/126100).

packages/flutter/lib/src/material/page_transitions_theme.dart

@@ -297,7 +297,7 @@ class _ZoomEnterTransition extends StatefulWidget {
   State<_ZoomEnterTransition> createState() => _ZoomEnterTransitionState();
 }
 
-class _ZoomEnterTransitionState extends State<_ZoomEnterTransition> with _ZoomTransitionBase {
+class _ZoomEnterTransitionState extends State<_ZoomEnterTransition> with _ZoomTransitionBase<_ZoomEnterTransition> {
   // See SnapshotWidget doc comment, this is disabled on web because the HTML backend doesn't
   // support this functionality and the canvaskit backend uses a single thread for UI and raster
   // work which diminishes the impact of this performance improvement.
@@ -406,7 +406,7 @@ class _ZoomExitTransition extends StatefulWidget {
   State<_ZoomExitTransition> createState() => _ZoomExitTransitionState();
 }
 
-class _ZoomExitTransitionState extends State<_ZoomExitTransition> with _ZoomTransitionBase {
+class _ZoomExitTransitionState extends State<_ZoomExitTransition> with _ZoomTransitionBase<_ZoomExitTransition> {
   late _ZoomExitTransitionPainter delegate;
 
   // See SnapshotWidget doc comment, this is disabled on web because the HTML backend doesn't
@@ -830,7 +830,7 @@ void _updateScaledTransform(Matrix4 transform, double scale, Size size) {
   transform.translate(-dx, -dy);
 }
 
-mixin _ZoomTransitionBase {
+mixin _ZoomTransitionBase<S extends StatefulWidget> on State<S> {
   bool get useSnapshot;
 
   // Don't rasterize if:
@@ -863,6 +863,12 @@ mixin _ZoomTransitionBase {
         controller.allowSnapshotting = useSnapshot;
     }
   }
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
 }
 
 class _ZoomEnterTransitionPainter extends SnapshotPainter {

packages/flutter/lib/src/widgets/drag_target.dart

@@ -885,6 +885,7 @@ class _DragAvatar<T extends Object> extends Drag {
     _leaveAllEntered();
     _activeTarget = null;
     _entry!.remove();
+    _entry!.dispose();
     _entry = null;
     // TODO(ianh): consider passing _entry as well so the client can perform an animation.
     onDragEnd?.call(velocity ?? Velocity.zero, _lastOffset!, wasAccepted);

packages/flutter/lib/src/widgets/navigator.dart

@@ -454,6 +454,7 @@ abstract class Route<T> {
   @protected
   void dispose() {
     _navigator = null;
+    _restorationScopeId.dispose();
   }
 
   /// Whether this route is the top-most route on the navigator.
@@ -3606,6 +3607,9 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
     for (final _RouteEntry entry in _history) {
       entry.dispose();
     }
+    _rawNextPagelessRestorationScopeId.dispose();
+    _serializableHistory.dispose();
+    userGestureInProgressNotifier.dispose();
     super.dispose();
     // don't unlock, so that the object becomes unusable
     assert(_debugLocked);

packages/flutter/lib/src/widgets/ticker_provider.dart

@@ -64,13 +64,13 @@ class TickerMode extends StatefulWidget {
     return widget?.enabled ?? true;
   }
 
-  /// Obtains a [ValueNotifier] from the [TickerMode] surrounding the `context`,
+  /// Obtains a [ValueListenable] from the [TickerMode] surrounding the `context`,
   /// which indicates whether tickers are enabled in the given subtree.
   ///
-  /// When that [TickerMode] enabled or disabled tickers, the notifier notifies
+  /// When that [TickerMode] enabled or disabled tickers, the listenable notifies
   /// its listeners.
   ///
-  /// While the [ValueNotifier] is stable for the lifetime of the surrounding
+  /// While the [ValueListenable] is stable for the lifetime of the surrounding
   /// [TickerMode], calling this method does not establish a dependency between
   /// the `context` and the [TickerMode] and the widget owning the `context`
   /// does not rebuild when the ticker mode changes from true to false or vice
@@ -79,7 +79,7 @@ class TickerMode extends StatefulWidget {
   /// [Ticker]. Since no dependency is established, the widget owning the
   /// `context` is also not informed when it is moved to a new location in the
   /// tree where it may have a different [TickerMode] ancestor. When this
-  /// happens, the widget must manually unsubscribe from the old notifier,
+  /// happens, the widget must manually unsubscribe from the old listenable,
   /// obtain a new one from the new ancestor [TickerMode] by calling this method
   /// again, and re-subscribe to it. [StatefulWidget]s can, for example, do this
   /// in [State.activate], which is called after the widget has been moved to
@@ -93,10 +93,10 @@ class TickerMode extends StatefulWidget {
   /// potential unnecessary rebuilds.
   ///
   /// In the absence of a [TickerMode] widget, this function returns a
-  /// [ValueNotifier], whose [ValueNotifier.value] is always true.
-  static ValueNotifier<bool> getNotifier(BuildContext context) {
+  /// [ValueListenable], whose [ValueListenable.value] is always true.
+  static ValueListenable<bool> getNotifier(BuildContext context) {
     final _EffectiveTickerMode? widget = context.getInheritedWidgetOfExactType<_EffectiveTickerMode>();
-    return widget?.notifier ?? ValueNotifier<bool>(true);
+    return widget?.notifier ?? const _ConstantValueListenable<bool>(true);
   }
 
   @override
@@ -228,7 +228,7 @@ mixin SingleTickerProviderStateMixin<T extends StatefulWidget> on State<T> imple
     super.dispose();
   }
 
-  ValueNotifier<bool>? _tickerModeNotifier;
+  ValueListenable<bool>? _tickerModeNotifier;
 
   @override
   void activate() {
@@ -245,7 +245,7 @@ mixin SingleTickerProviderStateMixin<T extends StatefulWidget> on State<T> imple
   }
 
   void _updateTickerModeNotifier() {
-    final ValueNotifier<bool> newNotifier = TickerMode.getNotifier(context);
+    final ValueListenable<bool> newNotifier = TickerMode.getNotifier(context);
     if (newNotifier == _tickerModeNotifier) {
       return;
     }
@@ -307,7 +307,7 @@ mixin TickerProviderStateMixin<T extends StatefulWidget> on State<T> implements
     _tickers!.remove(ticker);
   }
 
-  ValueNotifier<bool>? _tickerModeNotifier;
+  ValueListenable<bool>? _tickerModeNotifier;
 
   @override
   void activate() {
@@ -327,7 +327,7 @@ mixin TickerProviderStateMixin<T extends StatefulWidget> on State<T> implements
   }
 
   void _updateTickerModeNotifier() {
-    final ValueNotifier<bool> newNotifier = TickerMode.getNotifier(context);
+    final ValueListenable<bool> newNotifier = TickerMode.getNotifier(context);
     if (newNotifier == _tickerModeNotifier) {
       return;
     }
@@ -395,3 +395,22 @@ class _WidgetTicker extends Ticker {
     super.dispose();
   }
 }
+
+class _ConstantValueListenable<T> implements ValueListenable<T> {
+  const _ConstantValueListenable(this.value);
+
+  @override
+  void addListener(VoidCallback listener) {
+    // Intentionally left empty: Value cannot change, so we never have to
+    // notify registered listeners.
+  }
+
+  @override
+  void removeListener(VoidCallback listener) {
+    // Intentionally left empty: Value cannot change, so we never have to
+    // notify registered listeners.
+  }
+
+  @override
+  final T value;
+}

packages/flutter/test/animation/animation_sheet_test.dart

@@ -7,18 +7,20 @@
 @Tags(<String>['reduced-test-set'])
 library;
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../foundation/leak_tracking.dart';
+
 void main() {
   /*
    * Here lies tests for packages/flutter_test/lib/src/animation_sheet.dart
    * because [matchesGoldenFile] does not use Skia Gold in its native package.
    */
 
-  // TODO(polina-c): fix ValueNotifier not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('correctly records frames using display', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('correctly records frames using display', (WidgetTester tester) async {
     final AnimationSheetBuilder builder = AnimationSheetBuilder(frameSize: _DecuplePixels.size);
 
     await tester.pumpFrames(
@@ -54,9 +56,7 @@ void main() {
     await expectLater(find.byWidget(display), matchesGoldenFile('test.animation_sheet_builder.records.png'));
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56001
 
-  // TODO(polina-c): fix ValueNotifier not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('correctly wraps a row', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('correctly wraps a row', (WidgetTester tester) async {
     final AnimationSheetBuilder builder = AnimationSheetBuilder(frameSize: _DecuplePixels.size);
 
     const Duration duration = Duration(seconds: 2);
@@ -74,9 +74,7 @@ void main() {
     await expectLater(find.byWidget(display), matchesGoldenFile('test.animation_sheet_builder.wraps.png'));
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56001
 
-  // TODO(polina-c): fix Picture and Image not disposed and and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('correctly records frames using collate', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('correctly records frames using collate', (WidgetTester tester) async {
     final AnimationSheetBuilder builder = AnimationSheetBuilder(frameSize: _DecuplePixels.size);
 
     await tester.pumpFrames(
@@ -104,15 +102,16 @@ void main() {
       const Duration(milliseconds: 100),
     );
 
+    final ui.Image image = await builder.collate(5);
+
     await expectLater(
-      builder.collate(5),
+      image,
       matchesGoldenFile('test.animation_sheet_builder.collate.png'),
     );
+    image.dispose();
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56001
 
-  // TODO(polina-c): fix Picture and Image not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('use allLayers to record out-of-subtree contents', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('use allLayers to record out-of-subtree contents', (WidgetTester tester) async {
     final AnimationSheetBuilder builder = AnimationSheetBuilder(
       frameSize: const Size(8, 2),
       allLayers: true,
@@ -137,12 +136,14 @@ void main() {
       const Duration(milliseconds: 100),
     );
 
+    final ui.Image image = await builder.collate(5);
+
     await expectLater(
-      builder.collate(5),
+      image,
       matchesGoldenFile('test.animation_sheet_builder.out_of_tree.png'),
     );
+    image.dispose();
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56001
-
 }
 
 // An animation of a yellow pixel moving from left to right, in a container of

packages/flutter/test/animation/live_binding_test.dart

@@ -7,6 +7,8 @@
 @Tags(<String>['reduced-test-set'])
 library;
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -78,9 +80,7 @@ void main() {
     // Currently skipped due to daily flake: https://github.com/flutter/flutter/issues/87588
   }, skip: true); // Typically skip: isBrowser https://github.com/flutter/flutter/issues/42767
 
-  // TODO(polina-c): fix ValueNotifier not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('Should show event indicator for pointer events with setSurfaceSize', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('Should show event indicator for pointer events with setSurfaceSize', (WidgetTester tester) async {
     final AnimationSheetBuilder animationSheet = AnimationSheetBuilder(frameSize: const Size(200, 200), allLayers: true);
     final List<Offset> taps = <Offset>[];
     Widget target({bool recording = true}) => Container(
@@ -132,9 +132,12 @@ void main() {
     await tester.pumpFrames(target(), const Duration(milliseconds: 50));
     expect(taps, isEmpty);
 
+    final ui.Image image = await animationSheet.collate(6);
+
     await expectLater(
-      animationSheet.collate(6),
+      image,
       matchesGoldenFile('LiveBinding.press.animation.2.png'),
     );
+    image.dispose();
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56001
 }

packages/flutter/test/foundation/leak_tracking.dart

@@ -7,6 +7,8 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:leak_tracker/leak_tracker.dart';
 import 'package:meta/meta.dart';
 
+export 'package:leak_tracker/leak_tracker.dart' show LeakTrackingTestConfig, StackTraceCollectionConfig;
+
 /// Set of objects, that does not hold the objects from garbage collection.
 ///
 /// The objects are referenced by hash codes and can duplicate with low probability.

packages/flutter/test/gestures/gesture_config_regression_test.dart

@@ -114,9 +114,7 @@ void main() {
    expect(result.dragUpdate, true);
   });
 
-  // TODO(polina-c): fix ValueNotifier not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('Scroll Views get the same ScrollConfiguration as Draggables', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('Scroll Views get the same ScrollConfiguration as Draggables', (WidgetTester tester) async {
     tester.view.gestureSettings = const ui.GestureSettings(physicalTouchSlop: 4);
     addTearDown(tester.view.reset);
 

packages/flutter/test/material/about_test.dart

@@ -150,9 +150,7 @@ void main() {
     expect(find.text('About flutter_tester'), findsOneWidget);
   });
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage control test', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage control test', (WidgetTester tester) async {
     LicenseRegistry.addLicense(() {
       return Stream<LicenseEntry>.fromIterable(<LicenseEntry>[
         const LicenseEntryWithLineBreaks(<String>['AAA'], 'BBB'),
@@ -203,9 +201,7 @@ void main() {
     expect(find.text('Another license'), findsOneWidget);
   });
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage control test with all properties', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage control test with all properties', (WidgetTester tester) async {
     const FlutterLogo logo = FlutterLogo();
 
     LicenseRegistry.addLicense(() {
@@ -408,9 +404,7 @@ void main() {
     );
   });
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage returns early if unmounted', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage returns early if unmounted', (WidgetTester tester) async {
     final Completer<LicenseEntry> licenseCompleter = Completer<LicenseEntry>();
     LicenseRegistry.addLicense(() {
       return Stream<LicenseEntry>.fromFuture(licenseCompleter.future);
@@ -433,11 +427,9 @@ void main() {
     final FakeLicenseEntry licenseEntry = FakeLicenseEntry();
     licenseCompleter.complete(licenseEntry);
     expect(licenseEntry.packagesCalled, false);
-  });
+  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String>{'ValueNotifier<_OverlayEntryWidgetState?>'})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage returns late if unmounted', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage returns late if unmounted', (WidgetTester tester) async {
     final Completer<LicenseEntry> licenseCompleter = Completer<LicenseEntry>();
     LicenseRegistry.addLicense(() {
       return Stream<LicenseEntry>.fromFuture(licenseCompleter.future);
@@ -460,7 +452,7 @@ void main() {
 
     await tester.pumpAndSettle();
     expect(licenseEntry.packagesCalled, true);
-  });
+  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String>{'ValueNotifier<_OverlayEntryWidgetState?>'})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
 
   testWidgetsWithLeakTracking('LicensePage logic defaults to executable name for app name', (WidgetTester tester) async {
     await tester.pumpWidget(
@@ -1075,9 +1067,7 @@ void main() {
     expect(find.text('Exception: Injected failure'), findsOneWidget);
   });
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage master view layout position - ltr', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage master view layout position - ltr', (WidgetTester tester) async {
     const TextDirection textDirection = TextDirection.ltr;
     const Size defaultSize = Size(800.0, 600.0);
     const Size wideSize = Size(1200.0, 600.0);
@@ -1138,11 +1128,9 @@ void main() {
 
     // Configure to show the default layout.
     await tester.binding.setSurfaceSize(defaultSize);
-  });
+  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String>{'ValueNotifier<_OverlayEntryWidgetState?>'})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
 
-  // TODO(polina-c): fix SnapshotController not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('LicensePage master view layout position - rtl', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('LicensePage master view layout position - rtl', (WidgetTester tester) async {
     const TextDirection textDirection = TextDirection.rtl;
     const Size defaultSize = Size(800.0, 600.0);
     const Size wideSize = Size(1200.0, 600.0);
@@ -1203,7 +1191,7 @@ void main() {
 
     // Configure to show the default layout.
     await tester.binding.setSurfaceSize(defaultSize);
-  });
+  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String>{'ValueNotifier<_OverlayEntryWidgetState?>'})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
 
   testWidgetsWithLeakTracking('License page title in lateral UI does not use AppBarTheme.foregroundColor', (WidgetTester tester) async {
     // This is a regression test for https://github.com/flutter/flutter/issues/108991

packages/flutter/test/material/flutter_logo_test.dart

@@ -10,10 +10,10 @@ library;
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../foundation/leak_tracking.dart';
+
 void main() {
-  // TODO(polina-c): fix Image not disposed and switch to testWidgetsWithLeakTracking.
-  // https://github.com/flutter/devtools/issues/3951
-  testWidgets('Flutter Logo golden test', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('Flutter Logo golden test', (WidgetTester tester) async {
     final Key logo = UniqueKey();
     await tester.pumpWidget(FlutterLogo(key: logo));
 

packages/flutter_test/lib/src/_goldens_io.dart

@@ -201,13 +201,16 @@ Future<ComparisonResult> compareLists(List<int>? test, List<int>? master) async
   final int height = testImage.height;
 
   if (width != masterImage.width || height != masterImage.height) {
-    return ComparisonResult(
+    final ComparisonResult result =  ComparisonResult(
       passed: false,
       diffPercent: 1.0,
       error: 'Pixel test failed, image sizes do not match.\n'
         'Master Image: ${masterImage.width} X ${masterImage.height}\n'
         'Test Image: ${testImage.width} X ${testImage.height}',
     );
+    masterImage.dispose();
+    testImage.dispose();
+    return result;
   }
 
   int pixelDiffCount = 0;
@@ -264,6 +267,8 @@ Future<ComparisonResult> compareLists(List<int>? test, List<int>? master) async
       },
     );
   }
+  masterImage.dispose();
+  testImage.dispose();
   return ComparisonResult(passed: true, diffPercent: 0.0);
 }
 

packages/flutter_test/lib/src/_matchers_io.dart

@@ -78,10 +78,13 @@ class MatchesGoldenFile extends AsyncMatcher {
       }
     }
     Future<ui.Image?> imageFuture;
+    final bool disposeImage; // set to true if the matcher created and owns the image and must therefore dispose it.
     if (item is Future<ui.Image?>) {
       imageFuture = item;
+      disposeImage = false;
     } else if (item is ui.Image) {
       imageFuture = Future<ui.Image>.value(item);
+      disposeImage = false;
     } else if (item is Finder) {
       final Iterable<Element> elements = item.evaluate();
       if (elements.isEmpty) {
@@ -90,6 +93,7 @@ class MatchesGoldenFile extends AsyncMatcher {
         return 'matched too many widgets';
       }
       imageFuture = captureImage(elements.single);
+      disposeImage = true;
     } else {
       throw AssertionError('must provide a Finder, Image, Future<Image>, List<int>, or Future<List<int>>');
     }
@@ -100,19 +104,25 @@ class MatchesGoldenFile extends AsyncMatcher {
       if (image == null) {
         throw AssertionError('Future<Image> completed to null');
       }
-      final ByteData? bytes = await image.toByteData(format: ui.ImageByteFormat.png);
-      if (bytes == null) {
-        return 'could not encode screenshot.';
-      }
-      if (autoUpdateGoldenFiles) {
-        await goldenFileComparator.update(testNameUri, bytes.buffer.asUint8List());
-        return null;
-      }
       try {
-        final bool success = await goldenFileComparator.compare(bytes.buffer.asUint8List(), testNameUri);
-        return success ? null : 'does not match';
-      } on TestFailure catch (ex) {
-        return ex.message;
+        final ByteData? bytes = await image.toByteData(format: ui.ImageByteFormat.png);
+        if (bytes == null) {
+          return 'could not encode screenshot.';
+        }
+        if (autoUpdateGoldenFiles) {
+          await goldenFileComparator.update(testNameUri, bytes.buffer.asUint8List());
+          return null;
+        }
+        try {
+          final bool success = await goldenFileComparator.compare(bytes.buffer.asUint8List(), testNameUri);
+          return success ? null : 'does not match';
+        } on TestFailure catch (ex) {
+          return ex.message;
+        }
+      } finally {
+        if (disposeImage) {
+          image.dispose();
+        }
       }
     }, additionalTime: const Duration(minutes: 1));
   }

packages/flutter_test/lib/src/animation_sheet.dart

@@ -437,10 +437,13 @@ Future<ui.Image> _collateFrames(List<ui.Image> frames, Size frameSize, int cells
       Paint(),
     );
   }
-  return recorder.endRecording().toImage(
+  final ui.Picture picture = recorder.endRecording();
+  final ui.Image image = await picture.toImage(
     (frameSize.width * cellsPerRow).toInt(),
     (frameSize.height * rowNum).toInt(),
   );
+  picture.dispose();
+  return image;
 }
 
 // Layout children in a grid of fixed-sized cells.