Set track color in Cupertino Switch and Adaptive Switch (#45074)

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

@@ -60,6 +60,7 @@ class CupertinoSwitch extends StatefulWidget {
     @required this.value,
     @required this.onChanged,
     this.activeColor,
+    this.trackColor,
     this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(value != null),
        assert(dragStartBehavior != null),
@@ -100,6 +101,11 @@ class CupertinoSwitch extends StatefulWidget {
   /// the [CupertinoTheme] in accordance to native iOS behavior.
   final Color activeColor;
 
+  /// The color to use for the background when the switch is off.
+  ///
+  /// Defaults to [CupertinoColors.secondarySystemFill] when null.
+  final Color trackColor;
+
   /// {@template flutter.cupertino.switch.dragStartBehavior}
   /// Determines the way that drag start behavior is handled.
   ///
@@ -144,6 +150,7 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
           widget.activeColor ?? CupertinoColors.systemGreen,
           context,
         ),
+        trackColor: CupertinoDynamicColor.resolve(widget.trackColor ?? CupertinoColors.secondarySystemFill, context),
         onChanged: widget.onChanged,
         vsync: this,
         dragStartBehavior: widget.dragStartBehavior,
@@ -157,6 +164,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     Key key,
     this.value,
     this.activeColor,
+    this.trackColor,
     this.onChanged,
     this.vsync,
     this.dragStartBehavior = DragStartBehavior.start,
@@ -164,6 +172,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
 
   final bool value;
   final Color activeColor;
+  final Color trackColor;
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;
   final DragStartBehavior dragStartBehavior;
@@ -173,7 +182,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     return _RenderCupertinoSwitch(
       value: value,
       activeColor: activeColor,
-      trackColor: CupertinoDynamicColor.resolve(CupertinoColors.secondarySystemFill, context),
+      trackColor: trackColor,
       onChanged: onChanged,
       textDirection: Directionality.of(context),
       vsync: vsync,
@@ -186,7 +195,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     renderObject
       ..value = value
       ..activeColor = activeColor
-      ..trackColor = CupertinoDynamicColor.resolve(CupertinoColors.secondarySystemFill, context)
+      ..trackColor = trackColor
       ..onChanged = onChanged
       ..textDirection = Directionality.of(context)
       ..vsync = vsync

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

@@ -335,6 +335,7 @@ class _SwitchState extends State<Switch> with TickerProviderStateMixin {
           value: widget.value,
           onChanged: widget.onChanged,
           activeColor: widget.activeColor,
+          trackColor: widget.inactiveTrackColor
         ),
       ),
     );

packages/flutter/test/cupertino/switch_test.dart

@@ -7,6 +7,9 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+import '../rendering/mock_canvas.dart';
 
 void main() {
   testWidgets('Switch can toggle on tap', (WidgetTester tester) async {
@@ -433,6 +436,28 @@ void main() {
     expect(tester.widget<Opacity>(find.byType(Opacity).first).opacity, 0.5);
   });
 
+  testWidgets('Switch is using track color when set', (WidgetTester tester) async {
+    const Color trackColor = Color(0xFF00FF00);
+
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: CupertinoSwitch(
+            value: false,
+            trackColor: trackColor,
+            dragStartBehavior: DragStartBehavior.down,
+            onChanged: null,
+          ),
+        ),
+      ),
+    );
+
+    expect(find.byType(CupertinoSwitch), findsOneWidget);
+    expect(tester.widget<CupertinoSwitch>(find.byType(CupertinoSwitch)).trackColor, trackColor);
+    expect(find.byType(CupertinoSwitch), paints..rrect(color: trackColor));
+  });
+
   testWidgets('Switch is opaque when enabled', (WidgetTester tester) async {
     await tester.pumpWidget(
       Directionality(

packages/flutter/test/material/switch_test.dart

@@ -585,6 +585,7 @@ void main() {
 
   testWidgets('Switch.adaptive', (WidgetTester tester) async {
     bool value = false;
+    const Color inactiveTrackColor = Colors.pink;
 
     Widget buildFrame(TargetPlatform platform) {
       return MaterialApp(
@@ -595,6 +596,7 @@ void main() {
               child: Center(
                 child: Switch.adaptive(
                   value: value,
+                  inactiveTrackColor: inactiveTrackColor,
                   onChanged: (bool newValue) {
                     setState(() {
                       value = newValue;
@@ -611,6 +613,9 @@ void main() {
     await tester.pumpWidget(buildFrame(TargetPlatform.iOS));
     expect(find.byType(CupertinoSwitch), findsOneWidget);
 
+    final CupertinoSwitch adaptiveSwitch = tester.widget(find.byType(CupertinoSwitch));
+    expect(adaptiveSwitch.trackColor, inactiveTrackColor);
+
     expect(value, isFalse);
     await tester.tap(find.byType(Switch));
     expect(value, isTrue);