Add semantics to cupertino slider (#20476)

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

@@ -331,6 +331,7 @@ class _RenderCupertinoSlider extends RenderConstrainedBox {
       _position.animateTo(newValue, curve: Curves.fastOutSlowIn);
     else
       _position.value = newValue;
+    markNeedsSemanticsUpdate();
   }
 
   int get divisions => _divisions;
@@ -503,8 +504,12 @@ class _RenderCupertinoSlider extends RenderConstrainedBox {
 
     config.isSemanticBoundary = isInteractive;
     if (isInteractive) {
+      config.textDirection = textDirection;
       config.onIncrease = _increaseAction;
       config.onDecrease = _decreaseAction;
+      config.value = '${(value * 100).round()}%';
+      config.increasedValue = '${((value + _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
+      config.decreasedValue = '${((value - _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
     }
   }
 

packages/flutter/test/cupertino/slider_test.dart

@@ -289,6 +289,10 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            value: '50%',
+            increasedValue: '60%',
+            decreasedValue: '40%',
+            textDirection: TextDirection.ltr,
             actions: SemanticsAction.decrease.index | SemanticsAction.increase.index,
           ),
         ]
@@ -314,4 +318,45 @@ void main() {
 
     semantics.dispose();
   });
+
+  testWidgets('Slider Semantics can be updated', (WidgetTester tester) async {
+    final SemanticsHandle handle = tester.ensureSemantics();
+    double value = 0.5;
+    await tester.pumpWidget(new Directionality(
+      textDirection: TextDirection.ltr,
+      child: new CupertinoSlider(
+        value: value,
+        onChanged: (double v) { },
+      ),
+    ));
+
+    expect(tester.getSemanticsData(find.byType(CupertinoSlider)), matchesSemanticsData(
+      hasIncreaseAction: true,
+      hasDecreaseAction: true,
+      value: '50%',
+      increasedValue: '60%',
+      decreasedValue: '40%',
+      textDirection: TextDirection.ltr,
+    ));
+
+    value = 0.6;
+    await tester.pumpWidget(new Directionality(
+      textDirection: TextDirection.ltr,
+      child: new CupertinoSlider(
+        value: value,
+        onChanged: (double v) { },
+      ),
+    ));
+
+    expect(tester.getSemanticsData(find.byType(CupertinoSlider)), matchesSemanticsData(
+      hasIncreaseAction: true,
+      hasDecreaseAction: true,
+      value: '60%',
+      increasedValue: '70%',
+      decreasedValue: '50%',
+      textDirection: TextDirection.ltr,
+    ));
+
+    handle.dispose();
+  });
 }

packages/flutter_test/lib/src/matchers.dart

@@ -304,6 +304,8 @@ Matcher matchesSemanticsData({
   String label,
   String hint,
   String value,
+  String increasedValue,
+  String decreasedValue,
   TextDirection textDirection,
   Rect rect,
   Size size,
@@ -447,6 +449,8 @@ Matcher matchesSemanticsData({
     label: label,
     hint: hint,
     value: value,
+    increasedValue: increasedValue,
+    decreasedValue: decreasedValue,
     actions: actions,
     flags: flags,
     textDirection: textDirection,
@@ -1514,6 +1518,8 @@ class _MatchesSemanticsData extends Matcher {
   _MatchesSemanticsData({
     this.label,
     this.value,
+    this.increasedValue,
+    this.decreasedValue,
     this.hint,
     this.flags,
     this.actions,
@@ -1527,6 +1533,8 @@ class _MatchesSemanticsData extends Matcher {
   final String label;
   final String value;
   final String hint;
+  final String increasedValue;
+  final String decreasedValue;
   final SemanticsHintOverrides hintOverrides;
   final List<SemanticsAction> actions;
   final List<CustomSemanticsAction> customActions;
@@ -1544,6 +1552,10 @@ class _MatchesSemanticsData extends Matcher {
       description.add('with value: $value ');
     if (hint != null)
       description.add('with hint: $hint ');
+    if (increasedValue != null)
+      description.add('with increasedValue: $increasedValue');
+    if (decreasedValue != null)
+      description.add('with decreasedValue: $decreasedValue');
     if (actions != null)
       description.add('with actions:').addDescriptionOf(actions);
     if (flags != null)
@@ -1573,6 +1585,10 @@ class _MatchesSemanticsData extends Matcher {
       return failWithDescription(matchState, 'hint was: ${data.hint}');
     if (value != null && value != data.value)
       return failWithDescription(matchState, 'value was: ${data.value}');
+    if (increasedValue != null && increasedValue != data.increasedValue)
+      return failWithDescription(matchState, 'increasedValue was: ${data.increasedValue}');
+    if (decreasedValue != null && decreasedValue != data.decreasedValue)
+      return failWithDescription(matchState, 'decreasedValue was: ${data.decreasedValue}');
     if (textDirection != null && textDirection != data.textDirection)
       return failWithDescription(matchState, 'textDirection was: $textDirection');
     if (rect != null && rect != data.rect)

packages/flutter_test/test/matchers_test.dart

@@ -398,6 +398,8 @@ void main() {
         label: 'foo',
         hint: 'bar',
         value: 'baz',
+        increasedValue: 'a',
+        decreasedValue: 'b',
         textDirection: TextDirection.rtl,
         onTapHint: 'scan',
         onLongPressHint: 'fill',
@@ -412,6 +414,8 @@ void main() {
           label: 'foo',
           hint: 'bar',
           value: 'baz',
+          increasedValue: 'a',
+          decreasedValue: 'b',
           textDirection: TextDirection.rtl,
           hasTapAction: true,
           hasLongPressAction: true,