🐛 Setup color tween for `RefreshIndicator` in a better way (#134492)

Fixes https://github.com/flutter/flutter/issues/134489.

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

@@ -275,6 +275,7 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
   late Future<void> _pendingRefreshFuture;
   bool? _isIndicatorAtTop;
   double? _dragOffset;
+  late Color _effectiveValueColor = widget.color ?? Theme.of(context).colorScheme.primary;
 
   static final Animatable<double> _threeQuarterTween = Tween<double>(begin: 0.0, end: 0.75);
   static final Animatable<double> _kDragSizeFactorLimitTween = Tween<double>(begin: 0.0, end: _kDragSizeFactorLimit);
@@ -293,15 +294,7 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
 
   @override
   void didChangeDependencies() {
-    final ThemeData theme = Theme.of(context);
-    _valueColor = _positionController.drive(
-      ColorTween(
-        begin: (widget.color ?? theme.colorScheme.primary).withOpacity(0.0),
-        end: (widget.color ?? theme.colorScheme.primary).withOpacity(1.0),
-      ).chain(CurveTween(
-        curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit),
-      )),
-    );
+    _setupColorTween();
     super.didChangeDependencies();
   }
 
@@ -309,15 +302,7 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
   void didUpdateWidget(covariant RefreshIndicator oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.color != widget.color) {
-      final ThemeData theme = Theme.of(context);
-      _valueColor = _positionController.drive(
-        ColorTween(
-          begin: (widget.color ?? theme.colorScheme.primary).withOpacity(0.0),
-          end: (widget.color ?? theme.colorScheme.primary).withOpacity(1.0),
-        ).chain(CurveTween(
-            curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit),
-        )),
-      );
+      _setupColorTween();
     }
   }
 
@@ -328,6 +313,28 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
     super.dispose();
   }
 
+  void _setupColorTween() {
+    // Reset the current value color.
+    _effectiveValueColor = widget.color ?? Theme.of(context).colorScheme.primary;
+    final Color color = _effectiveValueColor;
+    if (color.alpha == 0x00) {
+      // Set an always stopped animation instead of a driven tween.
+      _valueColor = AlwaysStoppedAnimation<Color>(color);
+    } else {
+      // Respect the alpha of the given color.
+      _valueColor = _positionController.drive(
+        ColorTween(
+          begin: color.withAlpha(0),
+          end: color.withAlpha(color.alpha),
+        ).chain(
+          CurveTween(
+            curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit),
+          ),
+        ),
+      );
+    }
+  }
+
   bool _shouldStart(ScrollNotification notification) {
     // If the notification.dragDetails is null, this scroll is not triggered by
     // user dragging. It may be a result of ScrollController.jumpTo or ballistic scroll.
@@ -448,7 +455,7 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
       newValue = math.max(newValue, 1.0 / _kDragSizeFactorLimit);
     }
     _positionController.value = clampDouble(newValue, 0.0, 1.0); // this triggers various rebuilds
-    if (_mode == _RefreshIndicatorMode.drag && _valueColor.value!.alpha == 0xFF) {
+    if (_mode == _RefreshIndicatorMode.drag && _valueColor.value!.alpha == _effectiveValueColor.alpha) {
       _mode = _RefreshIndicatorMode.armed;
     }
   }

packages/flutter/test/material/refresh_indicator_test.dart

@@ -1070,4 +1070,67 @@ void main() {
     expect(refreshCalled, true);
     expect(stretchAccepted, false);
   });
+
+  testWidgetsWithLeakTracking('RefreshIndicator manipulates value color opacity correctly', (WidgetTester tester) async {
+    final List<Color> colors = <Color>[
+      Colors.black,
+      Colors.black54,
+      Colors.white,
+      Colors.white54,
+      Colors.transparent,
+    ];
+    const List<double> positions = <double>[50.0, 100.0, 150.0];
+
+    Future<void> testColor(Color color) async {
+      final AnimationController positionController = AnimationController(vsync: const TestVSync());
+      // Correspond to [_setupColorTween].
+      final Animation<Color?> valueColorAnimation = positionController.drive(
+        ColorTween(
+          begin: color.withAlpha(0),
+          end: color.withAlpha(color.alpha),
+        ).chain(
+          CurveTween(
+            // Correspond to [_kDragSizeFactorLimit].
+            curve: const Interval(0.0, 1.0 / 1.5),
+          ),
+        ),
+      );
+      await tester.pumpWidget(
+        MaterialApp(
+          home: RefreshIndicator(
+            onRefresh: refresh,
+            color: color,
+            child: ListView(
+              physics: const AlwaysScrollableScrollPhysics(),
+              children: const <Widget>[Text('X')],
+            ),
+          ),
+        ),
+      );
+
+      RefreshProgressIndicator getIndicator() {
+        return tester.widget<RefreshProgressIndicator>(
+          find.byType(RefreshProgressIndicator),
+        );
+      }
+
+      // Correspond to [_kDragContainerExtentPercentage].
+      final double maxPosition = tester.view.physicalSize.height / tester.view.devicePixelRatio * 0.25;
+      for (final double position in positions) {
+        await tester.fling(find.text('X'), Offset(0.0, position), 1.0);
+        await tester.pump();
+        positionController.value = position / maxPosition;
+        expect(
+          getIndicator().valueColor!.value!.alpha,
+          valueColorAnimation.value!.alpha,
+        );
+        // Wait until the fling finishes before starting the next fling.
+        await tester.pumpAndSettle();
+      }
+    }
+
+    for (final Color color in colors) {
+      await testColor(color);
+    }
+  });
 }