Missing default focus when navigating to a page with no SemanticsNode that sets namesRoute:true (#20516)

Author: chunhtai

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

@@ -1548,6 +1548,17 @@ private void sendWindowChangeEvent(@NonNull SemanticsNode route) {
     AccessibilityEvent event =
         obtainAccessibilityEvent(route.id, AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);
     String routeName = route.getRouteName();
+    if (routeName == null) {
+      // The routeName will be null when there is no semantics node that represnets namesRoute in
+      // the scopeRoute. The TYPE_WINDOW_STATE_CHANGED only works the route name is not null and not
+      // empty. Gives it a whitespace will make it focus the first semantics node without
+      // pronouncing any word.
+      //
+      // The other way to trigger a focus change is to send a TYPE_VIEW_FOCUSED to the
+      // rootAccessibilityView. However, it is less predictable which semantics node it will focus
+      // next.
+      routeName = " ";
+    }
     event.getText().add(routeName);
     sendAccessibilityEvent(event);
   }

shell/platform/android/test/io/flutter/view/AccessibilityBridgeTest.java

@@ -132,6 +132,41 @@ public void itUnfocusesPlatformViewWhenPlatformViewGoesAway() {
     assertEquals(event.getEventType(), AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUS_CLEARED);
   }
 
+  @Test
+  public void itAnnouncesWhiteSpaceWhenNoNamesRoute() {
+    AccessibilityViewEmbedder mockViewEmbedder = mock(AccessibilityViewEmbedder.class);
+    AccessibilityManager mockManager = mock(AccessibilityManager.class);
+    View mockRootView = mock(View.class);
+    Context context = mock(Context.class);
+    when(mockRootView.getContext()).thenReturn(context);
+    when(context.getPackageName()).thenReturn("test");
+    AccessibilityBridge accessibilityBridge =
+        setUpBridge(mockRootView, mockManager, mockViewEmbedder);
+    ViewParent mockParent = mock(ViewParent.class);
+    when(mockRootView.getParent()).thenReturn(mockParent);
+    when(mockManager.isEnabled()).thenReturn(true);
+
+    // Sent a11y tree with scopeRoute without namesRoute.
+    TestSemanticsNode root = new TestSemanticsNode();
+    root.id = 0;
+    TestSemanticsNode scopeRoute = new TestSemanticsNode();
+    scopeRoute.id = 1;
+    scopeRoute.addFlag(AccessibilityBridge.Flag.SCOPES_ROUTE);
+    root.children.add(scopeRoute);
+    TestSemanticsUpdate testSemanticsUpdate = root.toUpdate();
+    accessibilityBridge.updateSemantics(testSemanticsUpdate.buffer, testSemanticsUpdate.strings);
+
+    ArgumentCaptor<AccessibilityEvent> eventCaptor =
+        ArgumentCaptor.forClass(AccessibilityEvent.class);
+    verify(mockParent, times(2))
+        .requestSendAccessibilityEvent(eq(mockRootView), eventCaptor.capture());
+    AccessibilityEvent event = eventCaptor.getAllValues().get(0);
+    assertEquals(event.getEventType(), AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);
+    List<CharSequence> sentences = event.getText();
+    assertEquals(sentences.size(), 1);
+    assertEquals(sentences.get(0).toString(), " ");
+  }
+
   @Test
   public void itHoverOverOutOfBoundsDoesNotCrash() {
     // SementicsNode.hitTest() returns null when out of bounds.