Revert "CupertinoDatePicker & CupertinoTimerPicker dark mode (#39919)" (#41521)

bin/internal/goldens.version

-d19eee409dcf3348dea030b374e53a86f79b7de7
+0728c1b6e968602e173d0153a88d9cfb932d8c9b

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

@@ -24,6 +24,8 @@ const double _kDatePickerPadSize = 12.0;
 // The density of a date picker is different from a generic picker.
 // Eyeballed from iOS.
 const double _kSqueeze = 1.25;
+// Considers setting the default background color from the theme, in the future.
+const Color _kBackgroundColor = CupertinoColors.white;
 
 const TextStyle _kDefaultPickerTextStyle = TextStyle(
   letterSpacing: -0.83,
@@ -225,11 +227,12 @@ class CupertinoDatePicker extends StatefulWidget {
     this.maximumYear,
     this.minuteInterval = 1,
     this.use24hFormat = false,
-    this.backgroundColor,
+    this.backgroundColor = _kBackgroundColor,
   }) : initialDateTime = initialDateTime ?? DateTime.now(),
        assert(mode != null),
        assert(onDateTimeChanged != null),
        assert(minimumYear != null),
+       assert(backgroundColor != null),
        assert(
          minuteInterval > 0 && 60 % minuteInterval == 0,
          'minute interval is not a positive integer factor of 60',
@@ -299,7 +302,7 @@ class CupertinoDatePicker extends StatefulWidget {
 
   /// Background color of date picker.
   ///
-  /// Defaults to null, which disables background painting entirely.
+  /// Defaults to [CupertinoColors.white] when null.
   final Color backgroundColor;
 
   @override
@@ -1118,7 +1121,7 @@ class CupertinoTimerPicker extends StatefulWidget {
     this.minuteInterval = 1,
     this.secondInterval = 1,
     this.alignment = Alignment.center,
-    this.backgroundColor,
+    this.backgroundColor = _kBackgroundColor,
     @required this.onTimerDurationChanged,
   }) : assert(mode != null),
        assert(onTimerDurationChanged != null),
@@ -1128,6 +1131,7 @@ class CupertinoTimerPicker extends StatefulWidget {
        assert(secondInterval > 0 && 60 % secondInterval == 0),
        assert(initialTimerDuration.inMinutes % minuteInterval == 0),
        assert(initialTimerDuration.inSeconds % secondInterval == 0),
+       assert(backgroundColor != null),
        assert(alignment != null),
        super(key: key);
 
@@ -1155,7 +1159,7 @@ class CupertinoTimerPicker extends StatefulWidget {
 
   /// Background color of timer picker.
   ///
-  /// Defaults to null, which disables background painting entirely.
+  /// Defaults to [CupertinoColors.white] when null.
   final Color backgroundColor;
 
   @override
@@ -1562,7 +1566,7 @@ class _CupertinoTimerPickerState extends State<CupertinoTimerPicker> {
         child: Align(
           alignment: widget.alignment,
           child: Container(
-            color: CupertinoDynamicColor.resolve(widget.backgroundColor, context),
+            color: _kBackgroundColor,
             width: totalWidth,
             height: _kPickerHeight,
             child: DefaultTextStyle(

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

@@ -7,23 +7,19 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
-import 'colors.dart';
 import 'theme.dart';
 
 /// Color of the 'magnifier' lens border.
-const Color _kHighlighterBorder = CupertinoDynamicColor.withBrightness(
-  color: Color(0x33000000),
-  darkColor: Color(0x33FFFFFF),
-);
+const Color _kHighlighterBorder = Color(0xFF7F7F7F);
+const Color _kDefaultBackground = Color(0xFFD2D4DB);
 // Eyeballed values comparing with a native picker to produce the right
 // curvatures and densities.
 const double _kDefaultDiameterRatio = 1.07;
 const double _kDefaultPerspective = 0.003;
 const double _kSqueeze = 1.45;
-
-// Opacity fraction value that dims the wheel above and below the "magnifier"
-// lens.
-const double _kOverAndUnderCenterOpacity = 0.447;
+/// Opacity fraction value that hides the wheel above and below the 'magnifier'
+/// lens with the same color as the background.
+const double _kForegroundScreenOpacityFraction = 0.7;
 
 /// An iOS-styled picker.
 ///
@@ -65,7 +61,7 @@ class CupertinoPicker extends StatefulWidget {
   CupertinoPicker({
     Key key,
     this.diameterRatio = _kDefaultDiameterRatio,
-    this.backgroundColor,
+    this.backgroundColor = _kDefaultBackground,
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
@@ -108,7 +104,7 @@ class CupertinoPicker extends StatefulWidget {
   CupertinoPicker.builder({
     Key key,
     this.diameterRatio = _kDefaultDiameterRatio,
-    this.backgroundColor,
+    this.backgroundColor = _kDefaultBackground,
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
@@ -243,32 +239,110 @@ class _CupertinoPickerState extends State<CupertinoPicker> {
     }
   }
 
-  /// Draws the magnifier borders.
+  /// Makes the fade to [CupertinoPicker.backgroundColor] edge gradients.
+  Widget _buildGradientScreen() {
+    // Because BlendMode.dstOut doesn't work correctly with BoxDecoration we
+    // have to just do a color blend. And a due to the way we are layering
+    // the magnifier and the gradient on the background, using a transparent
+    // background color makes the picker look odd.
+    if (widget.backgroundColor != null && widget.backgroundColor.alpha < 255)
+      return Container();
+
+    final Color widgetBackgroundColor = widget.backgroundColor ?? const Color(0xFFFFFFFF);
+    return Positioned.fill(
+      child: IgnorePointer(
+        child: Container(
+          decoration: BoxDecoration(
+            gradient: LinearGradient(
+              colors: <Color>[
+                widgetBackgroundColor,
+                widgetBackgroundColor.withAlpha(0xF2),
+                widgetBackgroundColor.withAlpha(0xDD),
+                widgetBackgroundColor.withAlpha(0),
+                widgetBackgroundColor.withAlpha(0),
+                widgetBackgroundColor.withAlpha(0xDD),
+                widgetBackgroundColor.withAlpha(0xF2),
+                widgetBackgroundColor,
+              ],
+              stops: const <double>[
+                0.0, 0.05, 0.09, 0.22, 0.78, 0.91, 0.95, 1.0,
+              ],
+              begin: Alignment.topCenter,
+              end: Alignment.bottomCenter,
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+
+  /// Makes the magnifier lens look so that the colors are normal through
+  /// the lens and partially grayed out around it.
   Widget _buildMagnifierScreen() {
-    final Color resolvedBorderColor = CupertinoDynamicColor.resolve(_kHighlighterBorder, context);
+    final Color foreground = widget.backgroundColor?.withAlpha(
+      (widget.backgroundColor.alpha * _kForegroundScreenOpacityFraction).toInt()
+    );
 
     return IgnorePointer(
-      child: Center(
+      child: Column(
+        children: <Widget>[
+          Expanded(
             child: Container(
-          decoration: BoxDecoration(
+              color: foreground,
+            ),
+          ),
+          Container(
+            decoration: const BoxDecoration(
               border: Border(
-              top: BorderSide(width: 0.0, color: resolvedBorderColor),
-              bottom: BorderSide(width: 0.0, color: resolvedBorderColor),
+                top: BorderSide(width: 0.0, color: _kHighlighterBorder),
+                bottom: BorderSide(width: 0.0, color: _kHighlighterBorder),
               ),
             ),
             constraints: BoxConstraints.expand(
                 height: widget.itemExtent * widget.magnification,
             ),
           ),
+          Expanded(
+            child: Container(
+              color: foreground,
+            ),
+          ),
+        ],
       ),
     );
   }
 
+  Widget _buildUnderMagnifierScreen() {
+    final Color foreground = widget.backgroundColor?.withAlpha(
+        (widget.backgroundColor.alpha * _kForegroundScreenOpacityFraction).toInt()
+    );
+
+    return Column(
+      children: <Widget>[
+        Expanded(child: Container()),
+        Container(
+          color: foreground,
+          constraints: BoxConstraints.expand(
+            height: widget.itemExtent * widget.magnification,
+          ),
+        ),
+        Expanded(child: Container()),
+      ],
+    );
+  }
+
+  Widget _addBackgroundToChild(Widget child) {
+    return DecoratedBox(
+      decoration: BoxDecoration(
+        color: widget.backgroundColor,
+      ),
+      child: child,
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
-    final Color resolvedBackgroundColor = CupertinoDynamicColor.resolve(widget.backgroundColor, context);
-
-    final Widget result = DefaultTextStyle(
+    Widget result = DefaultTextStyle(
       style: CupertinoTheme.of(context).textTheme.pickerTextStyle,
       child: Stack(
         children: <Widget>[
@@ -283,7 +357,6 @@ class _CupertinoPickerState extends State<CupertinoPicker> {
                 offAxisFraction: widget.offAxisFraction,
                 useMagnifier: widget.useMagnifier,
                 magnification: widget.magnification,
-                overAndUnderCenterOpacity: _kOverAndUnderCenterOpacity,
                 itemExtent: widget.itemExtent,
                 squeeze: widget.squeeze,
                 onSelectedItemChanged: _handleSelectedItemChanged,
@@ -291,15 +364,24 @@ class _CupertinoPickerState extends State<CupertinoPicker> {
               ),
             ),
           ),
+          _buildGradientScreen(),
           _buildMagnifierScreen(),
         ],
       ),
     );
-
-    return DecoratedBox(
-      decoration: BoxDecoration(color: resolvedBackgroundColor),
-      child: result,
+    // Adds the appropriate opacity under the magnifier if the background
+    // color is transparent.
+    if (widget.backgroundColor != null && widget.backgroundColor.alpha < 255) {
+      result = Stack(
+        children: <Widget> [
+          _buildUnderMagnifierScreen(),
+          _addBackgroundToChild(result),
+        ],
       );
+    } else {
+      result = _addBackgroundToChild(result);
+    }
+    return result;
   }
 }
 

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

@@ -140,7 +140,6 @@ class RenderListWheelViewport
     double offAxisFraction = 0,
     bool useMagnifier = false,
     double magnification = 1,
-    double overAndUnderCenterOpacity = 1,
     @required double itemExtent,
     double squeeze = 1,
     bool clipToSize = true,
@@ -157,8 +156,6 @@ class RenderListWheelViewport
        assert(useMagnifier != null),
        assert(magnification != null),
        assert(magnification > 0),
-       assert(overAndUnderCenterOpacity != null),
-       assert(overAndUnderCenterOpacity >= 0 && overAndUnderCenterOpacity <= 1),
        assert(itemExtent != null),
        assert(squeeze != null),
        assert(squeeze > 0),
@@ -175,7 +172,6 @@ class RenderListWheelViewport
        _offAxisFraction = offAxisFraction,
        _useMagnifier = useMagnifier,
        _magnification = magnification,
-       _overAndUnderCenterOpacity = overAndUnderCenterOpacity,
        _itemExtent = itemExtent,
        _squeeze = squeeze,
        _clipToSize = clipToSize,
@@ -372,25 +368,6 @@ class RenderListWheelViewport
     markNeedsPaint();
   }
 
-  /// {@template flutter.rendering.wheelList.overAndUnderCenterOpacity}
-  /// The opacity value that will be applied to the wheel that appears below and
-  /// above the magnifier.
-  ///
-  /// The default value is 1.0, which will not change anything.
-  ///
-  /// Must be greater than or equal to 0, and less than or equal to 1.
-  /// {@endtemplate}
-  double get overAndUnderCenterOpacity => _overAndUnderCenterOpacity;
-  double _overAndUnderCenterOpacity = 1.0;
-  set overAndUnderCenterOpacity(double value) {
-    assert(value != null);
-    assert(value >= 0 && value <= 1);
-    if (value == _overAndUnderCenterOpacity)
-      return;
-    _overAndUnderCenterOpacity = value;
-    markNeedsPaint();
-  }
-
   /// {@template flutter.rendering.wheelList.itemExtent}
   /// The size of the children along the main axis. Children [RenderBox]es will
   /// be given the [BoxConstraints] of this exact size.
@@ -846,15 +823,19 @@ class RenderListWheelViewport
     // Offset that helps painting everything in the center (e.g. angle = 0).
     final Offset offsetToCenter = Offset(
         untransformedPaintingCoordinates.dx,
-      -_topScrollMarginExtent
-    );
+        -_topScrollMarginExtent);
 
-    final bool shouldApplyOffCenterDim = overAndUnderCenterOpacity < 1;
-    if (useMagnifier || shouldApplyOffCenterDim) {
-      _paintChildWithMagnifier(context, offset, child, transform, offsetToCenter, untransformedPaintingCoordinates);
-    } else {
+    if (!useMagnifier)
       _paintChildCylindrically(context, offset, child, transform, offsetToCenter);
-    }
+    else
+      _paintChildWithMagnifier(
+        context,
+        offset,
+        child,
+        transform,
+        offsetToCenter,
+        untransformedPaintingCoordinates,
+      );
   }
 
   /// Paint child with the magnifier active - the child will be rendered
@@ -897,22 +878,24 @@ class RenderListWheelViewport
 
       // Clipping the part in the center.
       context.pushClipRect(
-        needsCompositing,
+          false,
           offset,
           centerRect,
           (PaintingContext context, Offset offset) {
             context.pushTransform(
-            needsCompositing,
+              false,
               offset,
               _magnifyTransform(),
               (PaintingContext context, Offset offset) {
-              context.paintChild(child, offset + untransformedPaintingCoordinates);
+                context.paintChild(
+                  child,
+                  offset + untransformedPaintingCoordinates);
               });
           });
 
       // Clipping the part in either the top-half or bottom-half of the wheel.
       context.pushClipRect(
-        needsCompositing,
+          false,
           offset,
           untransformedPaintingCoordinates.dy <= magnifierTopLinePosition
             ? topHalfRect
@@ -944,26 +927,20 @@ class RenderListWheelViewport
     Matrix4 cylindricalTransform,
     Offset offsetToCenter,
   ) {
-    // Paint child with cylindrically.
-    final PaintingContextCallback painter = (PaintingContext context, Offset offset) {
+    context.pushTransform(
+      // Text with TransformLayers and no cullRects currently have an issue rendering
+      // https://github.com/flutter/flutter/issues/14224.
+      false,
+      offset,
+      _centerOriginTransform(cylindricalTransform),
+      // Pre-transform painting function.
+      (PaintingContext context, Offset offset) {
         context.paintChild(
           child,
           // Paint everything in the center (e.g. angle = 0), then transform.
           offset + offsetToCenter,
         );
-    };
-
-    // Paint child with cylindrically, with [overAndUnderCenterOpacity].
-    final PaintingContextCallback opacityPainter = (PaintingContext context, Offset offset) {
-      context.pushOpacity(offset, (overAndUnderCenterOpacity * 255).round(), painter);
-    };
-
-    context.pushTransform(
-      needsCompositing,
-      offset,
-      _centerOriginTransform(cylindricalTransform),
-      // Pre-transform painting function.
-      overAndUnderCenterOpacity == 1 ? painter : opacityPainter,
+      },
     );
   }
 

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

@@ -574,7 +574,6 @@ class ListWheelScrollView extends StatefulWidget {
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
-    this.overAndUnderCenterOpacity = 1.0,
     @required this.itemExtent,
     this.squeeze = 1.0,
     this.onSelectedItemChanged,
@@ -588,8 +587,6 @@ class ListWheelScrollView extends StatefulWidget {
        assert(perspective > 0),
        assert(perspective <= 0.01, RenderListWheelViewport.perspectiveTooHighMessage),
        assert(magnification > 0),
-       assert(overAndUnderCenterOpacity != null),
-       assert(overAndUnderCenterOpacity >= 0 && overAndUnderCenterOpacity <= 1),
        assert(itemExtent != null),
        assert(itemExtent > 0),
        assert(squeeze != null),
@@ -614,7 +611,6 @@ class ListWheelScrollView extends StatefulWidget {
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
-    this.overAndUnderCenterOpacity = 1.0,
     @required this.itemExtent,
     this.squeeze = 1.0,
     this.onSelectedItemChanged,
@@ -628,8 +624,6 @@ class ListWheelScrollView extends StatefulWidget {
        assert(perspective > 0),
        assert(perspective <= 0.01, RenderListWheelViewport.perspectiveTooHighMessage),
        assert(magnification > 0),
-       assert(overAndUnderCenterOpacity != null),
-       assert(overAndUnderCenterOpacity >= 0 && overAndUnderCenterOpacity <= 1),
        assert(itemExtent != null),
        assert(itemExtent > 0),
        assert(squeeze != null),
@@ -682,9 +676,6 @@ class ListWheelScrollView extends StatefulWidget {
   /// {@macro flutter.rendering.wheelList.magnification}
   final double magnification;
 
-  /// {@macro flutter.rendering.wheelList.overAndUnderCenterOpacity}
-  final double overAndUnderCenterOpacity;
-
   /// Size of each child in the main axis. Must not be null and must be
   /// positive.
   final double itemExtent;
@@ -765,7 +756,6 @@ class _ListWheelScrollViewState extends State<ListWheelScrollView> {
             offAxisFraction: widget.offAxisFraction,
             useMagnifier: widget.useMagnifier,
             magnification: widget.magnification,
-            overAndUnderCenterOpacity: widget.overAndUnderCenterOpacity,
             itemExtent: widget.itemExtent,
             squeeze: widget.squeeze,
             clipToSize: widget.clipToSize,
@@ -961,7 +951,6 @@ class ListWheelViewport extends RenderObjectWidget {
     this.offAxisFraction = 0.0,
     this.useMagnifier = false,
     this.magnification = 1.0,
-    this.overAndUnderCenterOpacity = 1.0,
     @required this.itemExtent,
     this.squeeze = 1.0,
     this.clipToSize = true,
@@ -975,8 +964,6 @@ class ListWheelViewport extends RenderObjectWidget {
        assert(perspective != null),
        assert(perspective > 0),
        assert(perspective <= 0.01, RenderListWheelViewport.perspectiveTooHighMessage),
-       assert(overAndUnderCenterOpacity != null),
-       assert(overAndUnderCenterOpacity >= 0 && overAndUnderCenterOpacity <= 1),
        assert(itemExtent != null),
        assert(itemExtent > 0),
        assert(squeeze != null),
@@ -1004,9 +991,6 @@ class ListWheelViewport extends RenderObjectWidget {
   /// {@macro flutter.rendering.wheelList.magnification}
   final double magnification;
 
-  /// {@macro flutter.rendering.wheelList.overAndUnderCenterOpacity}
-  final double overAndUnderCenterOpacity;
-
   /// {@macro flutter.rendering.wheelList.itemExtent}
   final double itemExtent;
 
@@ -1042,7 +1026,6 @@ class ListWheelViewport extends RenderObjectWidget {
       offAxisFraction: offAxisFraction,
       useMagnifier: useMagnifier,
       magnification: magnification,
-      overAndUnderCenterOpacity: overAndUnderCenterOpacity,
       itemExtent: itemExtent,
       squeeze: squeeze,
       clipToSize: clipToSize,
@@ -1059,7 +1042,6 @@ class ListWheelViewport extends RenderObjectWidget {
       ..offAxisFraction = offAxisFraction
       ..useMagnifier = useMagnifier
       ..magnification = magnification
-      ..overAndUnderCenterOpacity = overAndUnderCenterOpacity
       ..itemExtent = itemExtent
       ..squeeze = squeeze
       ..clipToSize = clipToSize

packages/flutter/test/cupertino/date_picker_test.dart

@@ -115,20 +115,19 @@ void main() {
       );
 
       final Iterable<CupertinoPicker> pickers = tester.allWidgets.whereType<CupertinoPicker>();
-      expect(pickers.any((CupertinoPicker picker) => picker.backgroundColor != null), false);
+      expect(pickers.any((CupertinoPicker picker) => picker.backgroundColor != CupertinoColors.white), false);
     });
 
-    testWidgets('background color can be null', (WidgetTester tester) async {
-      await tester.pumpWidget(
-        CupertinoApp(
-          home: CupertinoTimerPicker(
+    testWidgets('background color is not null', (WidgetTester tester) async {
+      expect(
+        () {
+          CupertinoTimerPicker(
             onTimerDurationChanged: (_) { },
             backgroundColor: null,
-          ),
-        ),
           );
-
-      expect(tester.takeException(), isNull);
+        },
+        throwsAssertionError,
+      );
     });
 
     testWidgets('specified background color is applied', (WidgetTester tester) async {
@@ -316,20 +315,19 @@ void main() {
       );
 
       final Iterable<CupertinoPicker> pickers = tester.allWidgets.whereType<CupertinoPicker>();
-      expect(pickers.any((CupertinoPicker picker) => picker.backgroundColor != null), false);
+      expect(pickers.any((CupertinoPicker picker) => picker.backgroundColor != CupertinoColors.white), false);
     });
 
-    testWidgets('background color can be null', (WidgetTester tester) async {
-      await tester.pumpWidget(
-        CupertinoApp(
-          home: CupertinoDatePicker(
+    testWidgets('background color is not null', (WidgetTester tester) async {
+      expect(
+        () {
+          CupertinoDatePicker(
             onDateTimeChanged: (_) { },
             backgroundColor: null,
-          ),
-        ),
           );
-
-      expect(tester.takeException(), isNull);
+        },
+        throwsAssertionError,
+      );
     });
 
     testWidgets('specified background color is applied', (WidgetTester tester) async {
@@ -926,7 +924,7 @@ void main() {
         find.byType(CupertinoDatePicker),
         matchesGoldenFile(
           'date_picker_test.datetime.initial.png',
-          version: 3,
+          version: 2,
         ),
       );
 
@@ -938,7 +936,7 @@ void main() {
         find.byType(CupertinoDatePicker),
         matchesGoldenFile(
           'date_picker_test.datetime.drag.png',
-          version: 3,
+          version: 2,
         ),
       );
     });
@@ -975,7 +973,7 @@ void main() {
       find.byType(CupertinoTimerPicker),
       matchesGoldenFile(
         'timer_picker_test.datetime.initial.png',
-        version: 2,
+        version: 1,
       ),
     );
 
@@ -987,7 +985,7 @@ void main() {
       find.byType(CupertinoTimerPicker),
       matchesGoldenFile(
         'timer_picker_test.datetime.drag.png',
-        version: 2,
+        version: 1,
       ),
     );
   });

packages/flutter/test/cupertino/picker_test.dart

@@ -7,8 +7,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
-
 void main() {
   testWidgets('Picker respects theme styling', (WidgetTester tester) async {
     await tester.pumpWidget(
@@ -95,56 +93,125 @@ void main() {
     });
   });
 
-  testWidgets('picker dark mode', (WidgetTester tester) async {
+  group('gradient', () {
+    testWidgets('gradient displays correctly with background color', (WidgetTester tester) async {
+      const Color backgroundColor = Color.fromRGBO(255, 0, 0, 1.0);
       await tester.pumpWidget(
-      CupertinoApp(
-        theme: const CupertinoThemeData(brightness: Brightness.light),
-        home: Align(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Align(
             alignment: Alignment.topLeft,
             child: SizedBox(
               height: 300.0,
               width: 300.0,
               child: CupertinoPicker(
-              backgroundColor: const CupertinoDynamicColor.withBrightness(
-                color: Color(0xFF123456), // Set alpha channel to FF to disable under magnifier painting.
-                darkColor: Color(0xFF654321),
-              ),
+                backgroundColor: backgroundColor,
                 itemExtent: 15.0,
-              children: const <Widget>[Text('1'), Text('1')],
+                children: const <Widget>[
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                ],
                 onSelectedItemChanged: (int i) { },
               ),
             ),
           ),
         ),
       );
+      final Container container = tester.firstWidget(find.byType(Container));
+      final BoxDecoration boxDecoration = container.decoration;
+      expect(boxDecoration.gradient.colors, <Color>[
+        backgroundColor,
+        backgroundColor.withAlpha(0xF2),
+        backgroundColor.withAlpha(0xDD),
+        backgroundColor.withAlpha(0x00),
+        backgroundColor.withAlpha(0x00),
+        backgroundColor.withAlpha(0xDD),
+        backgroundColor.withAlpha(0xF2),
+        backgroundColor,
+      ]);
+    });
 
-    expect(find.byType(CupertinoPicker), paints..path(color: const Color(0x33000000), style: PaintingStyle.stroke));
-    expect(find.byType(CupertinoPicker), paints..rect(color: const Color(0xFF123456)));
-
+    testWidgets('No gradient displays with transparent background color', (WidgetTester tester) async {
+      const Color backgroundColor = Color.fromRGBO(255, 0, 0, 0.5);
       await tester.pumpWidget(
-      CupertinoApp(
-        theme: const CupertinoThemeData(brightness: Brightness.dark),
-        home: Align(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Align(
             alignment: Alignment.topLeft,
             child: SizedBox(
               height: 300.0,
               width: 300.0,
               child: CupertinoPicker(
-              backgroundColor: const CupertinoDynamicColor.withBrightness(
-                color: Color(0xFF123456),
-                darkColor: Color(0xFF654321),
-              ),
+                backgroundColor: backgroundColor,
                 itemExtent: 15.0,
-              children: const <Widget>[Text('1'), Text('1')],
+                children: const <Widget>[
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                ],
                 onSelectedItemChanged: (int i) { },
               ),
             ),
           ),
         ),
       );
+      final DecoratedBox decoratedBox = tester.firstWidget(find.byType(DecoratedBox));
+      final BoxDecoration boxDecoration = decoratedBox.decoration;
+      expect(boxDecoration.gradient, isNull);
+      expect(boxDecoration.color, isNotNull);
+    });
 
-    expect(find.byType(CupertinoPicker), paints..path(color: const Color(0x33FFFFFF), style: PaintingStyle.stroke));
-    expect(find.byType(CupertinoPicker), paints..rect(color: const Color(0xFF654321)));
+    testWidgets('gradient displays correctly with null background color', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Align(
+            alignment: Alignment.topLeft,
+            child: SizedBox(
+              height: 300.0,
+              width: 300.0,
+              child: CupertinoPicker(
+                backgroundColor: null,
+                itemExtent: 15.0,
+                children: const <Widget>[
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                  Text('1'),
+                ],
+                onSelectedItemChanged: (int i) { },
+              ),
+            ),
+          ),
+        ),
+      );
+      // If the background color is null, the gradient color should be white.
+      const Color backgroundColor = Color(0xFFFFFFFF);
+      final Container container = tester.firstWidget(find.byType(Container));
+      final BoxDecoration boxDecoration = container.decoration;
+      expect(boxDecoration.gradient.colors, <Color>[
+        backgroundColor,
+        backgroundColor.withAlpha(0xF2),
+        backgroundColor.withAlpha(0xDD),
+        backgroundColor.withAlpha(0x00),
+        backgroundColor.withAlpha(0x00),
+        backgroundColor.withAlpha(0xDD),
+        backgroundColor.withAlpha(0xF2),
+        backgroundColor,
+      ]);
+    });
   });
 
   group('scroll', () {

packages/flutter/test/widgets/list_wheel_scroll_view_test.dart

@@ -64,63 +64,6 @@ void main() {
         throwsAssertionError,
       );
     });
-
-    testWidgets('ListWheelScrollView needs valid overAndUnderCenterOpacity', (WidgetTester tester) async {
-      expect(
-        () {
-          ListWheelScrollView(
-            overAndUnderCenterOpacity: null,
-            itemExtent: 20.0,
-            children: <Widget>[Container()],
-          );
-        },
-        throwsAssertionError,
-      );
-
-      expect(
-        () {
-          ListWheelScrollView(
-            overAndUnderCenterOpacity: -1,
-            itemExtent: 20.0,
-            children: <Widget>[Container()],
-          );
-        },
-        throwsAssertionError,
-      );
-
-      expect(
-        () {
-          ListWheelScrollView(
-            overAndUnderCenterOpacity: 2,
-            itemExtent: 20.0,
-            children: <Widget>[Container()],
-          );
-        },
-        throwsAssertionError,
-      );
-
-      expect(
-        () {
-          ListWheelScrollView(
-            overAndUnderCenterOpacity: 1,
-            itemExtent: 20.0,
-            children: <Widget>[Container()],
-          );
-        },
-        isNot(throwsAssertionError),
-      );
-
-      expect(
-        () {
-          ListWheelScrollView(
-            overAndUnderCenterOpacity: 0,
-            itemExtent: 20.0,
-            children: <Widget>[Container()],
-          );
-        },
-        isNot(throwsAssertionError),
-      );
-    });
   });
 
   group('infinite scrolling', () {
@@ -594,7 +537,7 @@ void main() {
         find.byKey(const Key('list_wheel_scroll_view')),
         matchesGoldenFile(
           'list_wheel_scroll_view.center_child.magnified.png',
-          version: 1,
+          version: null,
         ),
       );
     }, skip: isBrowser);
@@ -651,7 +594,7 @@ void main() {
         find.byKey(const Key('list_wheel_scroll_view')),
         matchesGoldenFile(
           'list_wheel_scroll_view.curved_wheel.left.png',
-          version: 1,
+          version: null,
         ),
       );
     }, skip: isBrowser);