Add isFocusable to SemanticsFlag

lib/ui/semantics.dart

@@ -290,6 +290,7 @@ class SemanticsFlag {
   static const int _kHasImplicitScrollingIndex = 1 << 18;
   static const int _kIsMultilineIndex = 1 << 19;
   static const int _kIsReadOnlyIndex = 1 << 20;
+  static const int _kIsFocusableIndex = 1 << 21;
 
   const SemanticsFlag._(this.index);
 
@@ -348,6 +349,11 @@ class SemanticsFlag {
   /// Only applicable when [isTextField] is true.
   static const SemanticsFlag isReadOnly = SemanticsFlag._(_kIsReadOnlyIndex);
 
+  /// Whether the semantic node is able to hold the user's focus.
+  ///
+  /// The focused element is usually the current receiver of keyboard inputs.
+  static const SemanticsFlag isFocusable = SemanticsFlag._(_kIsFocusableIndex);
+
   /// Whether the semantic node currently holds the user's focus.
   ///
   /// The focused element is usually the current receiver of keyboard inputs.

lib/ui/semantics/semantics_node.h

@@ -72,6 +72,7 @@ enum class SemanticsFlags : int32_t {
   // The Dart API defines the following flag but it isn't used in iOS.
   // kIsMultiline = 1 << 19,
   kIsReadOnly = 1 << 20,
+  kIsFocusable = 1 << 21,
 };
 
 const int kScrollableSemanticsFlags =

lib/web_ui/lib/src/ui/semantics.dart

@@ -293,6 +293,7 @@ class SemanticsFlag {
   static const int _kHasImplicitScrollingIndex = 1 << 18;
   static const int _kIsMultilineIndex = 1 << 19;
   static const int _kIsReadOnlyIndex = 1 << 20;
+  static const int _kIsFocusableIndex = 1 << 21;
 
   const SemanticsFlag._(this.index);
 
@@ -351,6 +352,11 @@ class SemanticsFlag {
   /// Only applicable when [isTextField] is true.
   static const SemanticsFlag isReadOnly = SemanticsFlag._(_kIsReadOnlyIndex);
 
+  /// Whether the semantic node is able to hold the user's focus.
+  ///
+  /// The focused element is usually the current receiver of keyboard inputs.
+  static const SemanticsFlag isFocusable = SemanticsFlag._(_kIsFocusableIndex);
+
   /// Whether the semantic node currently holds the user's focus.
   ///
   /// The focused element is usually the current receiver of keyboard inputs.
@@ -517,6 +523,7 @@ class SemanticsFlag {
     _kIsSelectedIndex: isSelected,
     _kIsButtonIndex: isButton,
     _kIsTextFieldIndex: isTextField,
+    _kIsFocusableIndex: isFocusable,
     _kIsFocusedIndex: isFocused,
     _kHasEnabledStateIndex: hasEnabledState,
     _kIsEnabledIndex: isEnabled,
@@ -548,6 +555,8 @@ class SemanticsFlag {
         return 'SemanticsFlag.isButton';
       case _kIsTextFieldIndex:
         return 'SemanticsFlag.isTextField';
+      case _kIsFocusableIndex:
+        return 'SemanticsFlag.isFocusable';
       case _kIsFocusedIndex:
         return 'SemanticsFlag.isFocused';
       case _kHasEnabledStateIndex:

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

@@ -1271,7 +1271,7 @@ void updateSemantics(@NonNull ByteBuffer buffer, @NonNull String[] strings) {
         }
         if (lastAdded != null && lastAdded.id != previousRouteId) {
             previousRouteId = lastAdded.id;
-            createAndSendWindowChangeEvent(lastAdded);
+            sendWindowChangeEvent(lastAdded);
         }
         flutterNavigationStack.clear();
         for (SemanticsNode semanticsNode : newRoutes) {
@@ -1290,7 +1290,7 @@ void updateSemantics(@NonNull ByteBuffer buffer, @NonNull String[] strings) {
 
         // TODO(goderbauer): Send this event only once (!) for changed subtrees,
         //     see https://github.com/flutter/flutter/issues/14534
-        sendAccessibilityEvent(0, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+        sendWindowContentChangeEvent(0);
 
         for (SemanticsNode object : updated) {
             if (object.didScroll()) {
@@ -1362,13 +1362,13 @@ void updateSemantics(@NonNull ByteBuffer buffer, @NonNull String[] strings) {
                 String label = object.label == null ? "" : object.label;
                 String previousLabel = object.previousLabel == null ? "" : object.label;
                 if (!label.equals(previousLabel) || !object.hadFlag(Flag.IS_LIVE_REGION)) {
-                    sendAccessibilityEvent(object.id, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+                    sendWindowContentChangeEvent(object.id);
                 }
             } else if (object.hasFlag(Flag.IS_TEXT_FIELD) && object.didChangeLabel()
                     && inputFocusedSemanticsNode != null && inputFocusedSemanticsNode.id == object.id) {
                 // Text fields should announce when their label changes while focused. We use a live
                 // region tag to do so, and this event triggers that update.
-                sendAccessibilityEvent(object.id, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+                sendWindowContentChangeEvent(object.id);
             }
             if (accessibilityFocusedSemanticsNode != null && accessibilityFocusedSemanticsNode.id == object.id
                     && !object.hadFlag(Flag.IS_SELECTED) && object.hasFlag(Flag.IS_SELECTED)) {
@@ -1472,13 +1472,13 @@ private void sendAccessibilityEvent(@NonNull AccessibilityEvent event) {
     }
 
     /**
-     * Factory method that creates a {@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED} and sends
-     * the event to Android's accessibility system.
+     * Creates a {@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED} and sends the event to
+     * Android's accessibility system.
      *
      * The given {@code route} should be a {@link SemanticsNode} that represents a navigation route
      * in the Flutter app.
      */
-    private void createAndSendWindowChangeEvent(@NonNull SemanticsNode route) {
+    private void sendWindowChangeEvent(@NonNull SemanticsNode route) {
         AccessibilityEvent event = obtainAccessibilityEvent(
             route.id,
             AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED
@@ -1488,6 +1488,27 @@ private void createAndSendWindowChangeEvent(@NonNull SemanticsNode route) {
         sendAccessibilityEvent(event);
     }
 
+    /**
+     * Creates a {@link AccessibilityEvent#TYPE_WINDOW_CONTENT_CHANGED} and sends the event to
+     * Android's accessibility system.
+     *
+     * It sets the content change types to {@link AccessibilityEvent#CONTENT_CHANGE_TYPE_SUBTREE}
+     * when supported by the API level.
+     *
+     * The given {@code virtualViewId} should be a {@link SemanticsNode} below which the content has
+     * changed.
+     */
+    private void sendWindowContentChangeEvent(int virtualViewId) {
+        AccessibilityEvent event = obtainAccessibilityEvent(
+            virtualViewId,
+            AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED
+        );
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
+            event.setContentChangeTypes(AccessibilityEvent.CONTENT_CHANGE_TYPE_SUBTREE);
+        }
+        sendAccessibilityEvent(event);
+    }
+
     /**
      * Factory method that creates a new {@link AccessibilityEvent} that is configured to represent
      * the Flutter {@link SemanticsNode} represented by the given {@code virtualViewId}, categorized
@@ -1559,7 +1580,7 @@ public void reset() {
         }
         accessibilityFocusedSemanticsNode = null;
         hoveredObject = null;
-        sendAccessibilityEvent(0, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+        sendWindowContentChangeEvent(0);
     }
 
     /**
@@ -1626,7 +1647,8 @@ private enum Flag {
         HAS_IMPLICIT_SCROLLING(1 << 18),
         // The Dart API defines the following flag but it isn't used in Android.
         // IS_MULTILINE(1 << 19);
-        IS_READ_ONLY(1 << 20);
+        IS_READ_ONLY(1 << 20),
+        IS_FOCUSABLE(1 << 21);
 
         final int value;
 
@@ -2000,6 +2022,12 @@ private boolean isFocusable() {
             if (hasFlag(Flag.SCOPES_ROUTE)) {
                 return false;
             }
+            if (hasFlag(Flag.IS_FOCUSABLE)) {
+                return true;
+            }
+            // If not explicitly set as focusable, then use our legacy
+            // algorithm. Once all focusable widgets have a Focus widget, then
+            // this won't be needed.
             int scrollableActions = Action.SCROLL_RIGHT.value | Action.SCROLL_LEFT.value
                     | Action.SCROLL_UP.value | Action.SCROLL_DOWN.value;
             return (actions & ~scrollableActions) != 0 || flags != 0