[ios] Announce zoom level, visible annotations after zooming

Announce the zoom level and number of visible annotations after zooming using VoiceOver’s swipe up or swipe down gesture.

Works toward #4821.

platform/ios/ios.xcodeproj/project.pbxproj

@@ -220,6 +220,8 @@
 		DABFB8711CBE9A0F00D62B32 /* MGLMapView+MGLCustomStyleLayerAdditions.h in Headers */ = {isa = PBXBuildFile; fileRef = DA8848381CBAFB8500AB86E3 /* MGLMapView+MGLCustomStyleLayerAdditions.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		DABFB8721CBE9A0F00D62B32 /* MGLUserLocation.h in Headers */ = {isa = PBXBuildFile; fileRef = DA8848391CBAFB8500AB86E3 /* MGLUserLocation.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		DABFB8731CBE9A9900D62B32 /* Mapbox.h in Headers */ = {isa = PBXBuildFile; fileRef = DA88485E1CBAFC2E00AB86E3 /* Mapbox.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		DAC49C5C1CD02BC9009E1AA3 /* Localizable.stringsdict in Resources */ = {isa = PBXBuildFile; fileRef = DAC49C5F1CD02BC9009E1AA3 /* Localizable.stringsdict */; };
+		DAC49C5D1CD02BC9009E1AA3 /* Localizable.stringsdict in Resources */ = {isa = PBXBuildFile; fileRef = DAC49C5F1CD02BC9009E1AA3 /* Localizable.stringsdict */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -459,6 +461,7 @@
 		DABCABBF1CB80717000A7C39 /* locations.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = locations.cpp; sourceTree = "<group>"; };
 		DABCABC01CB80717000A7C39 /* locations.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = locations.hpp; sourceTree = "<group>"; };
 		DAC07C961CBB2CD6000CB309 /* mbgl.xcconfig */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.xcconfig; name = mbgl.xcconfig; path = ../../build/ios/mbgl.xcconfig; sourceTree = "<group>"; };
+		DAC49C5E1CD02BC9009E1AA3 /* Base */ = {isa = PBXFileReference; lastKnownFileType = text.plist.stringsdict; name = Base; path = Base.lproj/Localizable.stringsdict; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -720,6 +723,7 @@
 			isa = PBXGroup;
 			children = (
 				DA89339F1CCC951200E68420 /* Localizable.strings */,
+				DAC49C5F1CD02BC9009E1AA3 /* Localizable.stringsdict */,
 				DA8848771CBAFD5C00AB86E3 /* api_mapbox_com-digicert.der */,
 				DA8848781CBAFD5C00AB86E3 /* api_mapbox_com-geotrust.der */,
 				DA8848791CBAFD5C00AB86E3 /* star_tilestream_net.der */,
@@ -1160,6 +1164,7 @@
 				DA8933F01CCD387900E68420 /* strip-frameworks.sh in Resources */,
 				DA8848751CBAFCC100AB86E3 /* mapbox@3x.png in Resources */,
 				DA88487B1CBAFD5C00AB86E3 /* api_mapbox_com-geotrust.der in Resources */,
+				DAC49C5C1CD02BC9009E1AA3 /* Localizable.stringsdict in Resources */,
 				DA8933BF1CCD2CAD00E68420 /* Foundation.stringsdict in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -1181,6 +1186,7 @@
 				DA8933DB1CCD31D400E68420 /* Foundation.strings in Resources */,
 				DA8933DC1CCD31D400E68420 /* Foundation.stringsdict in Resources */,
 				DA8933DD1CCD31D400E68420 /* api_mapbox_com-digicert.der in Resources */,
+				DAC49C5D1CD02BC9009E1AA3 /* Localizable.stringsdict in Resources */,
 				DA8933DE1CCD31D400E68420 /* api_mapbox_com-geotrust.der in Resources */,
 				DA8933DF1CCD31D400E68420 /* star_tilestream_net.der in Resources */,
 			);
@@ -1390,6 +1396,14 @@
 			name = LaunchScreen.storyboard;
 			sourceTree = "<group>";
 		};
+		DAC49C5F1CD02BC9009E1AA3 /* Localizable.stringsdict */ = {
+			isa = PBXVariantGroup;
+			children = (
+				DAC49C5E1CD02BC9009E1AA3 /* Base */,
+			);
+			name = Localizable.stringsdict;
+			sourceTree = "<group>";
+		};
 /* End PBXVariantGroup section */
 
 /* Begin XCBuildConfiguration section */

platform/ios/resources/Base.lproj/Localizable.strings

@@ -43,6 +43,9 @@
 /* Accessibility label */
 "MAP_A11Y_LABEL" = "Map";
 
+/* Map accessibility value */
+"MAP_A11Y_VALUE" = "Zoom %1$dx\n%2$ld annotation(s) visible";
+
 /* Action in attribution sheet */
 "MAP_FEEDBACK" = "Improve This Map";
 

platform/ios/resources/Base.lproj/Localizable.stringsdict

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>MAP_A11Y_VALUE</key>
+	<dict>
+		<key>NSStringLocalizedFormatKey</key>
+		<string>%#@count@</string>
+		<key>count</key>
+		<dict>
+			<key>NSStringFormatSpecTypeKey</key>
+			<string>NSStringPluralRuleType</string>
+			<key>NSStringFormatValueTypeKey</key>
+			<string>ld</string>
+			<key>zero</key>
+			<string>Zoom %dx
+no annotations visible</string>
+			<key>one</key>
+			<string>Zoom %dx
+%d annotation visible</string>
+			<key>other</key>
+			<string>Zoom %dx
+%d annotations visible</string>
+		</dict>
+	</dict>
+</dict>
+</plist>

platform/ios/src/MGLMapView.mm

@@ -1848,6 +1848,12 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
 
 #pragma mark - Accessibility -
 
+- (NSString *)accessibilityValue
+{
+    double zoomLevel = round(self.zoomLevel - 1);
+    return [NSString stringWithFormat:NSLocalizedStringWithDefaultValue(@"MAP_A11Y_VALUE", nil, nil, @"Zoom %dx\n%ld annotation(s) visible", @"Map accessibility value"), (int)zoomLevel, (long)self.accessibilityAnnotationCount];
+}
+
 - (CGRect)accessibilityFrame
 {
     CGRect frame = [super accessibilityFrame];
@@ -1881,8 +1887,7 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
     {
         return 2 /* selectedAnnotationCalloutView, mapViewProxyAccessibilityElement */;
     }
-    std::vector<MGLAnnotationTag> visibleAnnotations = [self annotationTagsInRect:self.bounds];
-    NSInteger count = visibleAnnotations.size() + 2 /* compass, userLocationAnnotationView, attributionButton */;
+    NSInteger count = self.accessibilityAnnotationCount + 2 /* compass, attributionButton */;
     if (self.userLocationAnnotationView)
     {
         count++;
@@ -1890,6 +1895,12 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
     return count;
 }
 
+- (NSInteger)accessibilityAnnotationCount
+{
+    std::vector<MGLAnnotationTag> visibleAnnotations = [self annotationTagsInRect:self.bounds];
+    return visibleAnnotations.size();
+}
+
 - (id)accessibilityElementAtIndex:(NSInteger)index
 {
     if (self.calloutViewForSelectedAnnotation)
@@ -2045,6 +2056,8 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
     }
     _mbglMap->scaleBy(scaleFactor, mbgl::ScreenCoordinate { centerPoint.x, centerPoint.y });
     [self unrotateIfNeededForGesture];
+    
+    UIAccessibilityPostNotification(UIAccessibilityAnnouncementNotification, self.accessibilityValue);
 }
 
 #pragma mark - Geography -