[ActionSheet] Add alert anouncement for voiceover users.

Similarly to how UIActionSheet announces "Alert" for voiceover users, we imitate the behavior here for MDCActionSheetController.

PiperOrigin-RevId: 316851432

components/ActionSheet/src/MDCActionSheetController.m

@@ -16,6 +16,8 @@
 
 #import "private/MDCActionSheetHeaderView.h"
 #import "private/MDCActionSheetItemTableViewCell.h"
+#import "private/MaterialActionSheetStrings.h"
+#import "private/MaterialActionSheetStrings_table.h"
 #import "MDCActionSheetControllerDelegate.h"
 #import "MaterialAvailability.h"
 #import "MaterialShadowElevations.h"
@@ -27,6 +29,9 @@
 static const CGFloat kActionTextAlpha = (CGFloat)0.87;
 static const CGFloat kDividerDefaultAlpha = (CGFloat)0.12;
 
+// The Bundle for string resources.
+static NSString *const kMaterialActionSheetBundle = @"MaterialActionSheet.bundle";
+
 @interface MDCActionSheetController () <MDCBottomSheetPresentationControllerDelegate,
                                         UITableViewDelegate,
                                         UITableViewDataSource>
@@ -203,6 +208,12 @@ - (void)viewDidLoad {
   [self.view addSubview:self.tableView];
   [self.view addSubview:self.header];
   [self.view addSubview:self.headerDividerView];
+
+  NSString *key =
+      kMaterialActionSheetStringTable[kStr_MaterialActionSheetPresentedAccessibilityAnnouncement];
+  NSString *announcement = NSLocalizedStringFromTableInBundle(
+      key, kMaterialActionSheetStringsTableName, [[self class] bundle], @"Alert");
+  UIAccessibilityPostNotification(UIAccessibilityScreenChangedNotification, announcement);
 }
 
 - (void)viewDidLayoutSubviews {
@@ -590,4 +601,22 @@ - (void)bottomSheetPresentationControllerDismissalAnimationCompleted:
   }
 }
 
+#pragma mark - Resource bundle
+
++ (NSBundle *)bundle {
+  static NSBundle *bundle = nil;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    bundle = [NSBundle bundleWithPath:[self bundlePathWithName:kMaterialActionSheetBundle]];
+  });
+
+  return bundle;
+}
+
++ (NSString *)bundlePathWithName:(NSString *)bundleName {
+  NSBundle *bundle = [NSBundle bundleForClass:[MDCActionSheetController class]];
+  NSString *resourcePath = [(nil == bundle ? [NSBundle mainBundle] : bundle) resourcePath];
+  return [resourcePath stringByAppendingPathComponent:bundleName];
+}
+
 @end

components/ActionSheet/src/MaterialActionSheet.bundle/Resources/en.lproj/MaterialActionSheet.strings

@@ -0,0 +1,2 @@
+/* Accessibility announcement when an action sheet is displayed. */
+"MaterialActionSheetPresentedAccessibilityAnnouncement" = "Alert";

components/ActionSheet/src/private/MaterialActionSheetStrings.h

@@ -0,0 +1,23 @@
+// Copyright 2020-present the Material Components for iOS authors. All Rights
+// Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// GENERATED CODE: DO NOT EDIT BY HAND
+// GENERATED FROM:
+// components/ActionSheet/src/MaterialActionSheet.bundle/Resources/en.lproj/MaterialActionSheet.strings
+// GENERATED BY: generate_string_tables.py
+
+typedef enum {
+  kStr_MaterialActionSheetPresentedAccessibilityAnnouncement = 0,
+} MaterialActionSheetStringId;

components/ActionSheet/src/private/MaterialActionSheetStrings_table.h

@@ -0,0 +1,31 @@
+// Copyright 2020-present the Material Components for iOS authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// GENERATED CODE: DO NOT EDIT BY HAND
+// GENERATED FROM:
+// components/ActionSheet/src/MaterialActionSheet.bundle/Resources/en.lproj/MaterialActionSheet.strings
+// GENERATED BY: generate_string_tables.py
+
+#import <Foundation/Foundation.h>
+
+// A table of string keys to look-up localized strings in the bundle.
+// This table is to be indexed using the generated enum.
+
+static NSString *const kMaterialActionSheetStringTable[] = {
+    @"MaterialActionSheetPresentedAccessibilityAnnouncement",  // Alert
+};
+#define kNumMaterialActionSheetStrings 1
+#define kMaterialActionSheetStringsOffset 0
+#define kMaterialActionSheetStringsEnd 10000
+static NSString *const kMaterialActionSheetStringsTableName = @"MaterialActionSheet";