Create general announcement system for non-Mac screenreaders.

This uses a method suggested by aleventhal@ in that it provides a hidden
view on each widget that can be used to send accessibility notifications
via the existing (at least on Mac) ViewAccessibility::AnnounceText()
method.

This CL expands AnnounceText() to be available on all platforms, with
the non-Mac implementation using an invisible view parented to the
widget's RootView.

Currently uses alerts since they are compatible with all screen readers.
Followup work will be to change to a live region update, which is a less
obtrusive alert (see crbug.com/1024898).

Bug: 1024026
Change-Id: I9dbe0d7e38fb69d3ada8b8e1574aee211bfe6291
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1913281Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#717237}

ui/views/accessibility/view_accessibility.cc

@@ -13,6 +13,7 @@
 #include "ui/accessibility/platform/ax_platform_node.h"
 #include "ui/base/buildflags.h"
 #include "ui/views/view.h"
+#include "ui/views/widget/root_view.h"
 #include "ui/views/widget/widget.h"
 
 namespace views {
@@ -291,6 +292,17 @@ gfx::NativeViewAccessible ViewAccessibility::GetNativeObject() {
   return nullptr;
 }
 
+void ViewAccessibility::AnnounceText(const base::string16& text) {
+  Widget* const widget = view_->GetWidget();
+  if (!widget)
+    return;
+  auto* const root_view =
+      static_cast<internal::RootView*>(widget->GetRootView());
+  if (!root_view)
+    return;
+  root_view->AnnounceText(text);
+}
+
 gfx::NativeViewAccessible ViewAccessibility::GetFocusedDescendant() {
   if (focused_virtual_child_)
     return focused_virtual_child_->GetNativeObject();

ui/views/accessibility/view_accessibility.h

@@ -89,9 +89,10 @@ class VIEWS_EXPORT ViewAccessibility {
 
   virtual gfx::NativeViewAccessible GetNativeObject();
   virtual void NotifyAccessibilityEvent(ax::mojom::Event event_type) {}
-#if defined(OS_MACOSX)
-  virtual void AnnounceText(base::string16& text) {}
-#endif
+
+  // Causes the screen reader to announce |text|. If the current user is not
+  // using a screen reader, has no effect.
+  virtual void AnnounceText(const base::string16& text);
 
   virtual const ui::AXUniqueId& GetUniqueId() const;
 

ui/views/accessibility/view_ax_platform_node_delegate.cc

@@ -191,7 +191,7 @@ void ViewAXPlatformNodeDelegate::NotifyAccessibilityEvent(
 }
 
 #if defined(OS_MACOSX)
-void ViewAXPlatformNodeDelegate::AnnounceText(base::string16& text) {
+void ViewAXPlatformNodeDelegate::AnnounceText(const base::string16& text) {
   ax_platform_node_->AnnounceText(text);
 }
 #endif

ui/views/accessibility/view_ax_platform_node_delegate.h

@@ -44,7 +44,7 @@ class ViewAXPlatformNodeDelegate : public ViewAccessibility,
   gfx::NativeViewAccessible GetNativeObject() override;
   void NotifyAccessibilityEvent(ax::mojom::Event event_type) override;
 #if defined(OS_MACOSX)
-  void AnnounceText(base::string16& text) override;
+  void AnnounceText(const base::string16& text) override;
 #endif
 
   // ui::AXPlatformNodeDelegate

ui/views/examples/BUILD.gn

@@ -9,6 +9,8 @@ jumbo_component("views_examples_lib") {
   testonly = true
 
   sources = [
+    "ax_example.cc",
+    "ax_example.h",
     "box_layout_example.cc",
     "box_layout_example.h",
     "bubble_example.cc",

ui/views/examples/ax_example.cc

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/views/examples/ax_example.h"
+
+#include "ui/views/accessibility/view_accessibility.h"
+#include "ui/views/background.h"
+#include "ui/views/controls/button/md_text_button.h"
+#include "ui/views/layout/flex_layout.h"
+#include "ui/views/view_class_properties.h"
+
+namespace views {
+namespace examples {
+
+AxExample::AxExample() : ExampleBase("Accessibility Features") {}
+
+AxExample::~AxExample() = default;
+
+void AxExample::CreateExampleView(View* container) {
+  container->SetBackground(CreateSolidBackground(SK_ColorWHITE));
+  FlexLayout* const layout =
+      container->SetLayoutManager(std::make_unique<FlexLayout>());
+  layout->SetCollapseMargins(true);
+  layout->SetOrientation(LayoutOrientation::kVertical);
+  layout->SetDefault(kMarginsKey, gfx::Insets(10));
+  layout->SetMainAxisAlignment(LayoutAlignment::kStart);
+  layout->SetCrossAxisAlignment(LayoutAlignment::kStart);
+
+  announce_button_ = container->AddChildView(
+      MdTextButton::Create(this, base::ASCIIToUTF16("AnnounceText")));
+}
+
+void AxExample::ButtonPressed(Button* sender, const ui::Event& event) {
+  sender->GetViewAccessibility().AnnounceText(
+      base::ASCIIToUTF16("Button pressed."));
+}
+
+}  // namespace examples
+}  // namespace views

ui/views/examples/ax_example.h

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_EXAMPLES_AX_EXAMPLE_H_
+#define UI_VIEWS_EXAMPLES_AX_EXAMPLE_H_
+
+#include "base/macros.h"
+#include "ui/views/controls/button/button.h"
+#include "ui/views/examples/example_base.h"
+
+namespace views {
+
+namespace examples {
+
+// ButtonExample simply counts the number of clicks.
+class VIEWS_EXAMPLES_EXPORT AxExample : public ExampleBase,
+                                        public ButtonListener {
+ public:
+  AxExample();
+  ~AxExample() override;
+
+  // ExampleBase:
+  void CreateExampleView(View* container) override;
+
+ private:
+  // ButtonListener:
+  void ButtonPressed(Button* sender, const ui::Event& event) override;
+
+  Button* announce_button_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(AxExample);
+};
+
+}  // namespace examples
+}  // namespace views
+
+#endif  // UI_VIEWS_EXAMPLES_AX_EXAMPLE_H_

ui/views/examples/examples_window.cc

@@ -19,6 +19,7 @@
 #include "ui/views/background.h"
 #include "ui/views/controls/combobox/combobox.h"
 #include "ui/views/controls/label.h"
+#include "ui/views/examples/ax_example.h"
 #include "ui/views/examples/box_layout_example.h"
 #include "ui/views/examples/bubble_example.h"
 #include "ui/views/examples/button_example.h"
@@ -61,6 +62,7 @@ namespace {
 // Creates the default set of examples.
 ExampleVector CreateExamples() {
   ExampleVector examples;
+  examples.push_back(std::make_unique<AxExample>());
   examples.push_back(std::make_unique<BoxLayoutExample>());
   examples.push_back(std::make_unique<BubbleExample>());
   examples.push_back(std::make_unique<ButtonExample>());

ui/views/widget/root_view.cc

@@ -9,6 +9,7 @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "build/build_config.h"
+#include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/base/cursor/cursor.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
@@ -48,6 +49,37 @@ class MouseEnterExitEvent : public ui::MouseEvent {
 
 }  // namespace
 
+// Used by RootView to create a hidden child that can be used to make screen
+// reader announcements on platforms that don't have a reliable system API call
+// to do that.
+//
+// We use a separate view because the RootView itself supplies the widget's
+// accessible name and cannot serve double-duty (the inability for views to make
+// their own announcements without changing their accessible name or description
+// is the reason this system exists at all).
+class AnnounceTextView : public View {
+ public:
+  ~AnnounceTextView() override = default;
+
+  void Announce(const base::string16& text) {
+    // TODO(crbug.com/1024898): Use kLiveRegionChanged when supported across
+    // screen readers and platforms. See bug for details.
+    announce_text_ = text;
+    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, true);
+  }
+
+  // View:
+  void GetAccessibleNodeData(ui::AXNodeData* node_data) override {
+    // TODO(crbug.com/1024898): Use live regions (do not use alerts).
+    // May require setting kLiveStatus, kContainerLiveStatus to "polite".
+    node_data->role = ax::mojom::Role::kAlert;
+    node_data->SetName(announce_text_);
+  }
+
+ private:
+  base::string16 announce_text_;
+};
+
 // This event handler receives events in the pre-target phase and takes care of
 // the following:
 //   - Shows keyboard-triggered context menus.
@@ -228,6 +260,21 @@ void RootView::DeviceScaleFactorChanged(float old_device_scale_factor,
                                           new_device_scale_factor);
 }
 
+// Accessibility ---------------------------------------------------------------
+
+void RootView::AnnounceText(const base::string16& text) {
+#if defined(OS_MACOSX)
+  // MacOSX has its own API for making announcements; see AnnounceText()
+  // override in ax_platform_node_mac.[h|mm]
+  NOTREACHED();
+#else
+  DCHECK(GetWidget());
+  if (!announce_view_)
+    announce_view_ = AddChildView(std::make_unique<AnnounceTextView>());
+  announce_view_->Announce(text);
+#endif
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // RootView, FocusTraversable implementation:
 
@@ -600,6 +647,14 @@ void RootView::UpdateParentLayer() {
     ReparentLayer(widget_->GetLayer());
 }
 
+void RootView::Layout() {
+  View::Layout();
+  // TODO(crbug.com/1026461): when FillLayout derives from LayoutManagerBase,
+  // just ignore the announce view instead of forcing it to zero size.
+  if (announce_view_)
+    announce_view_->SetSize({0, 0});
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // RootView, protected:
 

ui/views/widget/root_view.h

@@ -28,6 +28,7 @@ class Widget;
 // This is a views-internal API and should not be used externally.
 // Widget exposes this object as a View*.
 namespace internal {
+class AnnounceTextView;
 class PreEventDispatchHandler;
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -92,6 +93,11 @@ class VIEWS_EXPORT RootView : public View,
   void DeviceScaleFactorChanged(float old_device_scale_factor,
                                 float new_device_scale_factor);
 
+  // Accessibility -------------------------------------------------------------
+
+  // Make an announcement through the screen reader, if present.
+  void AnnounceText(const base::string16& text);
+
   // Overridden from FocusTraversable:
   FocusSearch* GetFocusSearch() override;
   FocusTraversable* GetFocusTraversableParent() override;
@@ -117,6 +123,7 @@ class VIEWS_EXPORT RootView : public View,
   void SetMouseHandler(View* new_mouse_handler) override;
   void GetAccessibleNodeData(ui::AXNodeData* node_data) override;
   void UpdateParentLayer() override;
+  void Layout() override;
 
  protected:
   // Overridden from View:
@@ -233,6 +240,12 @@ class VIEWS_EXPORT RootView : public View,
   // Tracks drag state for a view.
   View::DragInfo drag_info_;
 
+  // Accessibility -------------------------------------------------------------
+
+  // Hidden view used to make announcements to the screen reader via an alert or
+  // live region update.
+  AnnounceTextView* announce_view_ = nullptr;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(RootView);
 };