Add accessibilityFocus and loseAccessibilityFocus as a11y actions (flutter/engine#4655)

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

@@ -24,6 +24,8 @@ class SemanticsAction {
   static const int _kCopyIndex = 1 << 12;
   static const int _kCutIndex = 1 << 13;
   static const int _kPasteIndex = 1 << 14;
+  static const int _kDidGainAccessibilityFocusIndex = 1 << 15;
+  static const int _kDidLoseAccessibilityFocusIndex = 1 << 16;
 
   /// The numerical value for this action.
   ///
@@ -118,6 +120,32 @@ class SemanticsAction {
   /// Paste the current content of the clipboard.
   static const SemanticsAction paste = const SemanticsAction._(_kPasteIndex);
 
+  /// Indicates that the nodes has gained accessibility focus.
+  ///
+  /// This handler is invoked when the node annotated with this handler gains
+  /// the accessibility focus. The accessibility focus is the
+  /// green (on Android with TalkBack) or black (on iOS with VoiceOver)
+  /// rectangle shown on screen to indicate what element an accessibility
+  /// user is currently interacting with.
+  ///
+  /// The accessibility focus is different from the input focus. The input focus
+  /// is usually held by the element that currently responds to keyboard inputs.
+  /// Accessibility focus and input focus can be held by two different nodes!
+  static const SemanticsAction didGainAccessibilityFocus = const SemanticsAction._(_kDidGainAccessibilityFocusIndex);
+
+  /// Indicates that the nodes has lost accessibility focus.
+  ///
+  /// This handler is invoked when the node annotated with this handler
+  /// loses the accessibility focus. The accessibility focus is
+  /// the green (on Android with TalkBack) or black (on iOS with VoiceOver)
+  /// rectangle shown on screen to indicate what element an accessibility
+  /// user is currently interacting with.
+  ///
+  /// The accessibility focus is different from the input focus. The input focus
+  /// is usually held by the element that currently responds to keyboard inputs.
+  /// Accessibility focus and input focus can be held by two different nodes!
+  static const SemanticsAction didLoseAccessibilityFocus = const SemanticsAction._(_kDidLoseAccessibilityFocusIndex);
+
   /// The possible semantics actions.
   ///
   /// The map's key is the [index] of the action and the value is the action
@@ -138,6 +166,8 @@ class SemanticsAction {
     _kCopyIndex: copy,
     _kCutIndex: cut,
     _kPasteIndex: paste,
+    _kDidGainAccessibilityFocusIndex: didGainAccessibilityFocus,
+    _kDidLoseAccessibilityFocusIndex: didLoseAccessibilityFocus,
   };
 
   @override
@@ -173,6 +203,10 @@ class SemanticsAction {
         return 'SemanticsAction.cut';
       case _kPasteIndex:
         return 'SemanticsAction.paste';
+      case _kDidGainAccessibilityFocusIndex:
+        return 'SemanticsAction.didGainAccessibilityFocus';
+      case _kDidLoseAccessibilityFocusIndex:
+        return 'SemanticsAction.didLoseAccessibilityFocus';
     }
     return null;
   }

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

@@ -26,6 +26,15 @@ enum class SemanticsAction : int32_t {
   kScrollDown = 1 << 5,
   kIncrease = 1 << 6,
   kDecrease = 1 << 7,
+  kShowOnScreen = 1 << 8,
+  kMoveCursorForwardByCharacter = 1 << 9,
+  kMoveCursorBackwardByCharacter = 1 << 10,
+  kSetSelection = 1 << 11,
+  kCopy = 1 << 12,
+  kCut = 1 << 13,
+  kPaste = 1 << 14,
+  kDidGainAccessibilityFocus = 1 << 15,
+  kDidLoseAccessibilityFocus = 1 << 16,
 };
 
 const int kScrollableSemanticsActions =

engine/src/flutter/shell/platform/android/io/flutter/view/AccessibilityBridge.java

@@ -63,7 +63,9 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
         SET_SELECTION(1 << 11),
         COPY(1 << 12),
         CUT(1 << 13),
-        PASTE(1 << 14);
+        PASTE(1 << 14),
+        DID_GAIN_ACCESSIBILITY_FOCUS(1 << 15),
+        DID_LOSE_ACCESSIBILITY_FOCUS(1 << 16);
 
         Action(int value) {
             this.value = value;
@@ -312,11 +314,13 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
                 return performCursorMoveAction(object, virtualViewId, arguments, true);
             }
             case AccessibilityNodeInfo.ACTION_CLEAR_ACCESSIBILITY_FOCUS: {
+                mOwner.dispatchSemanticsAction(virtualViewId, Action.DID_LOSE_ACCESSIBILITY_FOCUS);
                 sendAccessibilityEvent(virtualViewId, AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUS_CLEARED);
                 mA11yFocusedObject = null;
                 return true;
             }
             case AccessibilityNodeInfo.ACTION_ACCESSIBILITY_FOCUS: {
+                mOwner.dispatchSemanticsAction(virtualViewId, Action.DID_GAIN_ACCESSIBILITY_FOCUS);
                 sendAccessibilityEvent(virtualViewId, AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUSED);
 
                 if (mA11yFocusedObject == null) {

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

@@ -257,6 +257,20 @@ bool GeometryComparator(SemanticsObject* a, SemanticsObject* b) {
   return YES;
 }
 
+#pragma mark UIAccessibilityFocus overrides
+
+- (void)accessibilityElementDidBecomeFocused {
+  if ([self node].HasAction(blink::SemanticsAction::kDidGainAccessibilityFocus)) {
+    [self bridge] -> DispatchSemanticsAction([self uid], blink::SemanticsAction::kDidGainAccessibilityFocus);
+  }
+}
+
+- (void)accessibilityElementDidLoseFocus {
+  if ([self node].HasAction(blink::SemanticsAction::kDidLoseAccessibilityFocus)) {
+    [self bridge] -> DispatchSemanticsAction([self uid], blink::SemanticsAction::kDidLoseAccessibilityFocus);
+  }
+}
+
 @end
 
 @implementation FlutterSemanticsObject {

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

@@ -224,10 +224,12 @@
 
 - (void)accessibilityElementDidBecomeFocused {
   [[self textInputSurrogate] accessibilityElementDidBecomeFocused];
+  [super accessibilityElementDidBecomeFocused];
 }
 
 - (void)accessibilityElementDidLoseFocus {
   [[self textInputSurrogate] accessibilityElementDidLoseFocus];
+  [super accessibilityElementDidLoseFocus];
 }
 
 - (BOOL)accessibilityElementIsFocused {