Announce the correct new value after increase/decrease has been performed on iOS (flutter/engine#4282)

engine/src/flutter/lib/ui/semantics.dart

@@ -215,9 +215,12 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
   /// with an action that is no longer possible.
   ///
   /// The `label` is a string that describes this node. The `value` property
-  /// describes the current value of the node as a string. The `hint` string
-  /// describes what result an action performed on this node has. The reading
-  /// direction of all these strings is given by `textDirection`.
+  /// describes the current value of the node as a string. The `increasedValue`
+  /// string will become the `value` string after a [SemanticsAction.increase]
+  /// action is performed. The `decreasedValue` string will become the `value`
+  /// string after a [SemanticsAction.decrease] action is performed. The `hint`
+  /// string describes what result an action performed on this node has. The
+  /// reading direction of all these strings is given by `textDirection`.
   ///
   /// The `rect` is the region occupied by this node in its own coordinate
   /// system.
@@ -232,6 +235,8 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     String label,
     String hint,
     String value,
+    String increasedValue,
+    String decreasedValue,
     TextDirection textDirection,
     Float64List transform,
     Int32List children
@@ -248,6 +253,8 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
                 label,
                 hint,
                 value,
+                increasedValue,
+                decreasedValue,
                 textDirection != null ? textDirection.index + 1 : 0,
                 transform,
                 children);
@@ -263,6 +270,8 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     String label,
     String hint,
     String value,
+    String increasedValue,
+    String decreasedValue,
     int textDirection,
     Float64List transform,
     Int32List children

engine/src/flutter/lib/ui/semantics/semantics_node.h

@@ -54,6 +54,8 @@ struct SemanticsNode {
   std::string label;
   std::string hint;
   std::string value;
+  std::string increasedValue;
+  std::string decreasedValue;
   int32_t textDirection = 0;  // 0=unknown, 1=rtl, 2=ltr
 
   SkRect rect = SkRect::MakeEmpty();

engine/src/flutter/lib/ui/semantics/semantics_update_builder.cc

@@ -44,6 +44,8 @@ void SemanticsUpdateBuilder::updateNode(int id,
                                         std::string label,
                                         std::string hint,
                                         std::string value,
+                                        std::string increasedValue,
+                                        std::string decreasedValue,
                                         int textDirection,
                                         const tonic::Float64List& transform,
                                         const tonic::Int32List& children) {
@@ -55,6 +57,8 @@ void SemanticsUpdateBuilder::updateNode(int id,
   node.label = label;
   node.hint = hint;
   node.value = value;
+  node.increasedValue = increasedValue;
+  node.decreasedValue = decreasedValue;
   node.textDirection = textDirection;
   node.transform.setColMajord(transform.data());
   node.children = std::vector<int32_t>(

engine/src/flutter/lib/ui/semantics/semantics_update_builder.h

@@ -35,6 +35,8 @@ class SemanticsUpdateBuilder
                   std::string label,
                   std::string hint,
                   std::string value,
+                  std::string increasedValue,
+                  std::string decreasedValue,
                   int textDirection,
                   const tonic::Float64List& transform,
                   const tonic::Int32List& children);

engine/src/flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm

@@ -245,12 +245,14 @@ bool GeometryComparator(SemanticsObject* a, SemanticsObject* b) {
 
 - (void)accessibilityIncrement {
   if (_node.HasAction(blink::SemanticsAction::kIncrease)) {
+    _node.value = _node.increasedValue;
     _bridge->DispatchSemanticsAction(_uid, blink::SemanticsAction::kIncrease);
   }
 }
 
 - (void)accessibilityDecrement {
   if (_node.HasAction(blink::SemanticsAction::kDecrease)) {
+    _node.value = _node.decreasedValue;
     _bridge->DispatchSemanticsAction(_uid, blink::SemanticsAction::kDecrease);
   }
 }