Enables semantics when voice control is turned on (#24640)

Author: chunhtai

ci/licenses_golden/licenses_flutter

@@ -1036,6 +1036,7 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterView.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterViewControllerTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterViewTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/IOKit.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.mm

shell/platform/darwin/ios/BUILD.gn

@@ -186,6 +186,7 @@ source_set("ios_test_flutter_mrc") {
     "framework/Source/FlutterEngineTest_mrc.mm",
     "framework/Source/FlutterPlatformPluginTest.mm",
     "framework/Source/FlutterPlatformViewsTest.mm",
+    "framework/Source/FlutterViewTest.mm",
     "framework/Source/accessibility_bridge_test.mm",
   ]
   deps = [

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -761,14 +761,20 @@ - (void)showAutocorrectionPromptRectForStart:(NSUInteger)start
                               arguments:@[ @(client), @(start), @(end) ]];
 }
 
-#pragma mark - Screenshot Delegate
+#pragma mark - FlutterViewEngineDelegate
 
 - (flutter::Rasterizer::Screenshot)takeScreenshot:(flutter::Rasterizer::ScreenshotType)type
                                   asBase64Encoded:(BOOL)base64Encode {
   FML_DCHECK(_shell) << "Cannot takeScreenshot without a shell";
   return _shell->Screenshot(type, base64Encode);
 }
 
+- (void)flutterViewAccessibilityDidCall {
+  if (self.viewController.view.accessibilityElements == nil) {
+    [self ensureSemanticsEnabled];
+  }
+}
+
 - (NSObject<FlutterBinaryMessenger>*)binaryMessenger {
   return _binaryMessenger;
 }

shell/platform/darwin/ios/framework/Source/FlutterEngineTest_mrc.mm

@@ -12,6 +12,18 @@
 
 FLUTTER_ASSERT_NOT_ARC
 
+@interface FlutterEngineSpy : FlutterEngine
+@property(nonatomic) BOOL ensureSemanticsEnabledCalled;
+@end
+
+@implementation FlutterEngineSpy
+
+- (void)ensureSemanticsEnabled {
+  _ensureSemanticsEnabledCalled = YES;
+}
+
+@end
+
 @interface FlutterEngineTest_mrc : XCTestCase
 @end
 
@@ -41,4 +53,11 @@ - (void)testSpawnsShareGpuContext {
   [spawn release];
 }
 
+- (void)testEnableSemanticsWhenFlutterViewAccessibilityDidCall {
+  FlutterEngineSpy* engine = [[FlutterEngineSpy alloc] initWithName:@"foobar"];
+  engine.ensureSemanticsEnabledCalled = NO;
+  [engine flutterViewAccessibilityDidCall];
+  XCTAssertTrue(engine.ensureSemanticsEnabledCalled);
+}
+
 @end

shell/platform/darwin/ios/framework/Source/FlutterView.h

@@ -21,6 +21,16 @@
                                   asBase64Encoded:(BOOL)base64Encode;
 
 - (std::shared_ptr<flutter::FlutterPlatformViewsController>&)platformViewsController;
+
+/**
+ * A callback that is called when iOS queries accessibility information of the Flutter view.
+ *
+ * This is useful to predict the current iOS accessibility status. For example, there is
+ * no API to listen whether voice control is turned on or off. The Flutter engine uses
+ * this callback to enable semantics in order to catch the case that voice control is
+ * on.
+ */
+- (void)flutterViewAccessibilityDidCall;
 @end
 
 @interface FlutterView : UIView

shell/platform/darwin/ios/framework/Source/FlutterView.mm

@@ -130,4 +130,17 @@ - (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context {
   CGContextRestoreGState(context);
 }
 
+- (BOOL)isAccessibilityElement {
+  // iOS does not provide an API to query whether the voice control
+  // is turned on or off. It is likely at least one of the assitive
+  // technologies is turned on if this method is called. If we do
+  // not catch it in notification center, we will catch it here.
+  //
+  // TODO(chunhtai): Remove this workaround once iOS provides an
+  // API to query whether voice control is enabled.
+  // https://github.com/flutter/flutter/issues/76808.
+  [_delegate flutterViewAccessibilityDidCall];
+  return NO;
+}
+
 @end

shell/platform/darwin/ios/framework/Source/FlutterViewTest.mm

@@ -0,0 +1,52 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <XCTest/XCTest.h>
+
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterView.h"
+
+@interface FakeDelegate : NSObject <FlutterViewEngineDelegate>
+@property(nonatomic) BOOL callbackCalled;
+@end
+
+@implementation FakeDelegate {
+  std::shared_ptr<flutter::FlutterPlatformViewsController> _platformViewsController;
+}
+
+- (instancetype)init {
+  _callbackCalled = NO;
+  _platformViewsController = std::shared_ptr<flutter::FlutterPlatformViewsController>(nullptr);
+  return self;
+}
+
+- (flutter::Rasterizer::Screenshot)takeScreenshot:(flutter::Rasterizer::ScreenshotType)type
+                                  asBase64Encoded:(BOOL)base64Encode {
+  return {};
+}
+
+- (std::shared_ptr<flutter::FlutterPlatformViewsController>&)platformViewsController {
+  return _platformViewsController;
+}
+
+- (void)flutterViewAccessibilityDidCall {
+  _callbackCalled = YES;
+}
+
+@end
+
+@interface FlutterViewTest : XCTestCase
+@end
+
+@implementation FlutterViewTest
+
+- (void)testFlutterViewEnableSemanticsWhenIsAccessibilityElementIsCalled {
+  FakeDelegate* delegate = [[FakeDelegate alloc] init];
+  FlutterView* view = [[FlutterView alloc] initWithDelegate:delegate opaque:NO];
+  delegate.callbackCalled = NO;
+  XCTAssertFalse(view.isAccessibilityElement);
+  XCTAssertTrue(delegate.callbackCalled);
+}
+
+@end