Properly update semantics when Material/Cupertino Sliders are disabled (#11776)

* Properly update semantics when Material/Cupertino Slider are disabled

* whitespace fix

* fix style

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

@@ -190,12 +190,13 @@ class _RenderCupertinoSlider extends RenderConstrainedBox implements SemanticsAc
     @required double value,
     int divisions,
     Color activeColor,
-    this.onChanged,
+    ValueChanged<double> onChanged,
     TickerProvider vsync,
   }) : assert(value != null && value >= 0.0 && value <= 1.0),
        _value = value,
        _divisions = divisions,
        _activeColor = activeColor,
+       _onChanged = onChanged,
        super(additionalConstraints: const BoxConstraints.tightFor(width: _kSliderWidth, height: _kSliderHeight)) {
     _drag = new HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
@@ -239,7 +240,16 @@ class _RenderCupertinoSlider extends RenderConstrainedBox implements SemanticsAc
     markNeedsPaint();
   }
 
-  ValueChanged<double> onChanged;
+  ValueChanged<double> get onChanged => _onChanged;
+  ValueChanged<double> _onChanged;
+  set onChanged(ValueChanged<double> value) {
+    if (value == _onChanged)
+      return;
+    final bool wasInteractive = isInteractive;
+    _onChanged = value;
+    if (wasInteractive != isInteractive)
+      markNeedsSemanticsUpdate(noGeometry: true);
+  }
 
   AnimationController _position;
 

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

@@ -288,7 +288,7 @@ class _RenderSlider extends RenderBox implements SemanticsActionHandler {
     Color inactiveColor,
     bool thumbOpenAtMin,
     TextTheme textTheme,
-    this.onChanged,
+    ValueChanged<double> onChanged,
     TickerProvider vsync,
   }) : assert(value != null && value >= 0.0 && value <= 1.0),
        _value = value,
@@ -296,7 +296,8 @@ class _RenderSlider extends RenderBox implements SemanticsActionHandler {
        _activeColor = activeColor,
        _inactiveColor = inactiveColor,
        _thumbOpenAtMin = thumbOpenAtMin,
-       _textTheme = textTheme {
+       _textTheme = textTheme,
+       _onChanged = onChanged {
     this.label = label;
     final GestureArenaTeam team = new GestureArenaTeam();
     _drag = new HorizontalDragGestureRecognizer()
@@ -401,7 +402,18 @@ class _RenderSlider extends RenderBox implements SemanticsActionHandler {
     markNeedsPaint();
   }
 
-  ValueChanged<double> onChanged;
+  ValueChanged<double> get onChanged => _onChanged;
+  ValueChanged<double> _onChanged;
+  set onChanged(ValueChanged<double> value) {
+    if (value == _onChanged)
+      return;
+    final bool wasInteractive = isInteractive;
+    _onChanged = value;
+    if (wasInteractive != isInteractive) {
+      markNeedsPaint();
+      markNeedsSemanticsUpdate(noGeometry: true);
+    }
+  }
 
   double get _trackLength => size.width - 2.0 * _kReactionRadius;
 

packages/flutter/test/cupertino/slider_test.dart

@@ -4,9 +4,12 @@
 
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../widgets/semantics_tester.dart';
+
 void main() {
   testWidgets('Slider does not move when tapped', (WidgetTester tester) async {
     final Key sliderKey = new UniqueKey();
@@ -77,4 +80,44 @@ void main() {
     // that no animation is running.
     expect(SchedulerBinding.instance.transientCallbackCount, equals(0));
   });
+
+  testWidgets('Slider Semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      new CupertinoSlider(
+        value: 0.5,
+        onChanged: (double v) {},
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics.rootChild(
+            id: 1,
+            actions: SemanticsAction.decrease.index | SemanticsAction.increase.index,
+          ),
+        ]
+      ),
+      ignoreRect: true,
+      ignoreTransform: true,
+    ));
+
+    // Disable slider
+    await tester.pumpWidget(
+      new CupertinoSlider(
+        value: 0.5,
+        onChanged: null,
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(),
+      ignoreRect: true,
+      ignoreTransform: true,
+    ));
+
+    semantics.dispose();
+  });
 }

packages/flutter/test/material/slider_test.dart

@@ -2,11 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
+import '../widgets/semantics_tester.dart';
 
 void main() {
   testWidgets('Slider can move when tapped', (WidgetTester tester) async {
@@ -295,4 +299,48 @@ void main() {
     ));
     expect(tester.renderObject<RenderBox>(find.byType(Slider)).size, const Size(144.0 + 2.0 * 16.0, 32.0));
   });
+
+  testWidgets('Slider Semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      new Material(
+        child: new Slider(
+          value: 0.5,
+          onChanged: (double v) {},
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+          children: <TestSemantics>[
+            new TestSemantics.rootChild(
+              id: 1,
+              actions: SemanticsAction.decrease.index | SemanticsAction.increase.index,
+            ),
+          ]
+      ),
+      ignoreRect: true,
+      ignoreTransform: true,
+    ));
+
+    // Disable slider
+    await tester.pumpWidget(
+      new Material(
+        child: new Slider(
+          value: 0.5,
+          onChanged: null,
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(),
+      ignoreRect: true,
+      ignoreTransform: true,
+    ));
+
+    semantics.dispose();
+  });
 }