Dispose Paragraph objects (#110627)

dev/benchmarks/macrobenchmarks/lib/src/web/bench_pageview_scroll_linethrough.dart

@@ -36,6 +36,7 @@ class _MyScrollContainerState extends State<_MyScrollContainer> {
   static const Duration stepDuration = Duration(milliseconds: 500);
 
   late PageController pageController;
+  final _CustomPainter _painter =  _CustomPainter('aa');
   int pageNumber = 0;
 
   @override
@@ -57,6 +58,7 @@ class _MyScrollContainerState extends State<_MyScrollContainer> {
   @override
   void dispose() {
     pageController.dispose();
+    _painter._textPainter.dispose();
     super.dispose();
   }
 
@@ -66,7 +68,7 @@ class _MyScrollContainerState extends State<_MyScrollContainer> {
         controller: pageController,
         itemBuilder: (BuildContext context, int position) {
           return CustomPaint(
-            painter: _CustomPainter('aa'),
+            painter: _painter,
             size: const Size(300, 500),
           );
         });

dev/integration_tests/flutter_gallery/lib/demo/transformations/transformations_demo.dart

@@ -182,6 +182,7 @@ class BoardPainter extends CustomPainter {
       );
       final Vertices vertices = board!.getVerticesForBoardPoint(boardPoint, color);
       canvas.drawVertices(vertices, BlendMode.color, Paint());
+      vertices.dispose();
     }
 
     board!.forEach(drawBoardPoint);

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -482,8 +482,11 @@ class CupertinoDatePicker extends StatefulWidget {
     // because there's no other way to get the information we want without
     // laying out the text.
     painter.layout();
-
-    return painter.maxIntrinsicWidth;
+    try {
+      return painter.maxIntrinsicWidth;
+    } finally {
+      painter.dispose();
+    }
   }
 }
 
@@ -1663,6 +1666,7 @@ class _CupertinoTimerPickerState extends State<CupertinoTimerPicker> {
   @override
   void dispose() {
     PaintingBinding.instance.systemFonts.removeListener(_handleSystemFontsChange);
+    textPainter.dispose();
     super.dispose();
   }
 

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

@@ -1090,6 +1090,13 @@ class _RenderRangeSlider extends RenderBox with RelayoutWhenSystemFontsChangeMix
     super.detach();
   }
 
+  @override
+  void dispose() {
+    _startLabelPainter.dispose();
+    _endLabelPainter.dispose();
+    super.dispose();
+  }
+
   double _getValueFromVisualPosition(double visualPosition) {
     switch (textDirection) {
       case TextDirection.rtl:

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

@@ -1342,6 +1342,12 @@ class _RenderSlider extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     super.detach();
   }
 
+  @override
+  void dispose() {
+    _labelPainter.dispose();
+    super.dispose();
+  }
+
   double _getValueFromVisualPosition(double visualPosition) {
     switch (textDirection) {
       case TextDirection.rtl:

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

@@ -860,6 +860,17 @@ class _DialPainter extends CustomPainter {
 
   static const double _labelPadding = 28.0;
 
+  void dispose() {
+    for (final _TappableLabel label in primaryLabels) {
+      label.painter.dispose();
+    }
+    for (final _TappableLabel label in secondaryLabels) {
+      label.painter.dispose();
+    }
+    primaryLabels.clear();
+    secondaryLabels.clear();
+  }
+
   @override
   void paint(Canvas canvas, Size size) {
     final double radius = size.shortestSide / 2.0;
@@ -966,6 +977,7 @@ class _DialState extends State<_Dial> with SingleTickerProviderStateMixin {
   late ThemeData themeData;
   late MaterialLocalizations localizations;
   late MediaQueryData media;
+  _DialPainter? painter;
 
   @override
   void didChangeDependencies() {
@@ -989,6 +1001,7 @@ class _DialState extends State<_Dial> with SingleTickerProviderStateMixin {
   @override
   void dispose() {
     _thetaController.dispose();
+    painter?.dispose();
     super.dispose();
   }
 
@@ -1280,6 +1293,18 @@ class _DialState extends State<_Dial> with SingleTickerProviderStateMixin {
         break;
     }
 
+    painter?.dispose();
+    painter = _DialPainter(
+      selectedValue: selectedDialValue,
+      primaryLabels: primaryLabels,
+      secondaryLabels: secondaryLabels,
+      backgroundColor: backgroundColor,
+      accentColor: accentColor,
+      dotColor: theme.colorScheme.surface,
+      theta: _theta.value,
+      textDirection: Directionality.of(context),
+    );
+
     return GestureDetector(
       excludeFromSemantics: true,
       onPanStart: _handlePanStart,
@@ -1288,16 +1313,7 @@ class _DialState extends State<_Dial> with SingleTickerProviderStateMixin {
       onTapUp: _handleTapUp,
       child: CustomPaint(
         key: const ValueKey<String>('time-picker-dial'),
-        painter: _DialPainter(
-          selectedValue: selectedDialValue,
-          primaryLabels: primaryLabels,
-          secondaryLabels: secondaryLabels,
-          backgroundColor: backgroundColor,
-          accentColor: accentColor,
-          dotColor: theme.colorScheme.surface,
-          theta: _theta.value,
-          textDirection: Directionality.of(context),
-        ),
+        painter: painter,
       ),
     );
   }

packages/flutter/lib/src/painting/flutter_logo.dart

@@ -227,6 +227,7 @@ class _FlutterLogoPainter extends BoxPainter {
   final FlutterLogoDecoration _config;
 
   // these are configured assuming a font size of 100.0.
+  // TODO(dnfield): Figure out how to dispose this https://github.com/flutter/flutter/issues/110601
   late TextPainter _textPainter;
   late Rect _textBoundingRect;
 

packages/flutter/lib/src/painting/text_painter.dart

@@ -222,6 +222,7 @@ class TextPainter {
   bool _rebuildParagraphForPaint = true;
 
   bool get _debugAssertTextLayoutIsValid {
+    assert(!debugDisposed);
     if (_paragraph == null) {
       throw FlutterError.fromParts(<DiagnosticsNode>[
         ErrorSummary('Text layout not available'),
@@ -247,6 +248,7 @@ class TextPainter {
       }
       return true;
     }());
+    _paragraph?.dispose();
     _paragraph = null;
     _lineMetricsCache = null;
     _previousCaretPosition = null;
@@ -271,6 +273,7 @@ class TextPainter {
       return;
     }
     if (_text?.style != value?.style) {
+      _layoutTemplate?.dispose();
       _layoutTemplate = null;
     }
 
@@ -329,6 +332,7 @@ class TextPainter {
     }
     _textDirection = value;
     markNeedsLayout();
+    _layoutTemplate?.dispose();
     _layoutTemplate = null; // Shouldn't really matter, but for strict correctness...
   }
 
@@ -347,6 +351,7 @@ class TextPainter {
     }
     _textScaleFactor = value;
     markNeedsLayout();
+    _layoutTemplate?.dispose();
     _layoutTemplate = null;
   }
 
@@ -1060,4 +1065,33 @@ class TextPainter {
     assert(_debugAssertTextLayoutIsValid);
     return  _lineMetricsCache ??= _paragraph!.computeLineMetrics();
   }
+
+  bool _disposed = false;
+
+  /// Whether this object has been disposed or not.
+  ///
+  /// Only for use when asserts are enabled.
+  bool get debugDisposed {
+    bool? disposed;
+    assert(() {
+      disposed = _disposed;
+      return true;
+    }());
+    return disposed ?? (throw StateError('debugDisposed only available when asserts are on.'));
+  }
+
+  /// Releases the resources associated with this painter.
+  ///
+  /// After disposal this painter is unusable.
+  void dispose() {
+    assert(() {
+      _disposed = true;
+      return true;
+    }());
+    _layoutTemplate?.dispose();
+    _layoutTemplate = null;
+    _paragraph?.dispose();
+    _paragraph = null;
+    _text = null;
+  }
 }

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

@@ -114,6 +114,14 @@ mixin DebugOverflowIndicatorMixin on RenderObject {
     TextPainter(textDirection: TextDirection.ltr), // This label is in English.
   );
 
+  @override
+  void dispose() {
+    for (final TextPainter painter in _indicatorLabel) {
+      painter.dispose();
+    }
+    super.dispose();
+  }
+
   // Set to true to trigger a debug message in the console upon
   // the next paint call. Will be reset after each paint.
   bool _overflowReportNeeded = true;

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

@@ -388,6 +388,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     _autocorrectHighlightPainter.dispose();
     _selectionPainter.dispose();
     _caretPainter.dispose();
+    _textPainter.dispose();
     super.dispose();
   }
 

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

@@ -256,6 +256,7 @@ class RenderParagraph extends RenderBox
     // _lastSelectableFragments may hold references to this RenderParagraph.
     // Release them manually to avoid retain cycles.
     _lastSelectableFragments = null;
+    _textPainter.dispose();
     super.dispose();
   }
 
@@ -864,6 +865,7 @@ class RenderParagraph extends RenderBox
               <Color>[const Color(0xFFFFFFFF), const Color(0x00FFFFFF)],
             );
           }
+          fadeSizePainter.dispose();
           break;
       }
     } else {

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

@@ -1515,6 +1515,13 @@ abstract class _RenderCustomClip<T> extends RenderProxyBox {
       return true;
     }());
   }
+
+  @override
+  void dispose() {
+    _debugText?.dispose();
+    _debugText = null;
+    super.dispose();
+  }
 }
 
 /// Clips its child using a rectangle.

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

@@ -117,14 +117,23 @@ class BannerPainter extends CustomPainter {
   );
 
   bool _prepared = false;
-  late TextPainter _textPainter;
+  TextPainter? _textPainter;
   late Paint _paintShadow;
   late Paint _paintBanner;
 
+  /// Release resources held by this painter.
+  ///
+  /// After calling this method, this object is no longer usable.
+  void dispose() {
+    _textPainter?.dispose();
+    _textPainter = null;
+  }
+
   void _prepare() {
     _paintShadow = _shadow.toPaint();
     _paintBanner = Paint()
       ..color = color;
+    _textPainter?.dispose();
     _textPainter = TextPainter(
       text: TextSpan(style: textStyle, text: message),
       textAlign: TextAlign.center,
@@ -144,8 +153,8 @@ class BannerPainter extends CustomPainter {
       ..drawRect(_kRect, _paintShadow)
       ..drawRect(_kRect, _paintBanner);
     const double width = _kOffset * 2.0;
-    _textPainter.layout(minWidth: width, maxWidth: width);
-    _textPainter.paint(canvas, _kRect.topLeft + Offset(0.0, (_kRect.height - _textPainter.height) / 2.0));
+    _textPainter!.layout(minWidth: width, maxWidth: width);
+    _textPainter!.paint(canvas, _kRect.topLeft + Offset(0.0, (_kRect.height - _textPainter!.height) / 2.0));
   }
 
   @override

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

@@ -339,6 +339,7 @@ class _SemanticsDebuggerPainter extends CustomPainter {
       ..layout(maxWidth: rect.width);
 
     textPainter.paint(canvas, Alignment.center.inscribe(textPainter.size, rect).topLeft);
+    textPainter.dispose();
     canvas.restore();
   }
 

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

@@ -2777,6 +2777,13 @@ class _InspectorOverlayLayer extends Layer {
   TextPainter? _textPainter;
   double? _textPainterMaxWidth;
 
+  @override
+  void dispose() {
+    _textPainter?.dispose();
+    _textPainter = null;
+    super.dispose();
+  }
+
   @override
   void addToScene(ui.SceneBuilder builder) {
     if (!selection.active) {
@@ -2878,6 +2885,7 @@ class _InspectorOverlayLayer extends Layer {
     final TextSpan? textSpan = _textPainter?.text as TextSpan?;
     if (_textPainter == null || textSpan!.text != message || _textPainterMaxWidth != maxWidth) {
       _textPainterMaxWidth = maxWidth;
+      _textPainter?.dispose();
       _textPainter = TextPainter()
         ..maxLines = _kMaxTooltipLines
         ..ellipsis = '...'