Re-lands platform brightness support on iOS

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

@@ -32,6 +32,20 @@ @interface FlutterViewController () <FlutterBinaryMessenger>
 @property(nonatomic, readwrite, getter=isDisplayingFlutterUI) BOOL displayingFlutterUI;
 @end
 
+// The following conditional compilation defines an API 13 concept on earlier API targets so that
+// a compiler compiling against API 12 or below does not blow up due to non-existent members.
+#if __IPHONE_OS_VERSION_MAX_ALLOWED < 130000
+typedef enum UIAccessibilityContrast : NSInteger {
+  UIAccessibilityContrastUnspecified = 0,
+  UIAccessibilityContrastNormal = 1,
+  UIAccessibilityContrastHigh = 2
+} UIAccessibilityContrast;
+
+@interface UITraitCollection (MethodsFromNewerSDK)
+- (UIAccessibilityContrast)accessibilityContrast;
+@end
+#endif
+
 @implementation FlutterViewController {
   std::unique_ptr<fml::WeakPtrFactory<FlutterViewController>> _weakFactory;
   fml::scoped_nsobject<FlutterEngine> _engine;
@@ -434,6 +448,9 @@ - (void)viewWillAppear:(BOOL)animated {
     _engineNeedsLaunch = NO;
   }
 
+  // Send platform settings to Flutter, e.g., platform brightness.
+  [self onUserSettingsChanged:nil];
+
   // Only recreate surface on subsequent appearances when viewport metrics are known.
   // First time surface creation is done on viewDidLayoutSubviews.
   if (_viewportMetrics.physical_width) {
@@ -885,10 +902,17 @@ - (void)onLocaleUpdated:(NSNotification*)notification {
 
 #pragma mark - Set user settings
 
+- (void)traitCollectionDidChange:(UITraitCollection*)previousTraitCollection {
+  [super traitCollectionDidChange:previousTraitCollection];
+  [self onUserSettingsChanged:nil];
+}
+
 - (void)onUserSettingsChanged:(NSNotification*)notification {
   [[_engine.get() settingsChannel] sendMessage:@{
     @"textScaleFactor" : @([self textScaleFactor]),
     @"alwaysUse24HourFormat" : @([self isAlwaysUse24HourFormat]),
+    @"platformBrightness" : [self brightnessMode],
+    @"platformContrast" : [self contrastMode]
   }];
 }
 
@@ -962,6 +986,40 @@ - (BOOL)isAlwaysUse24HourFormat {
   return [dateFormat rangeOfString:@"a"].location == NSNotFound;
 }
 
+// The brightness mode of the platform, e.g., light or dark, expressed as a string that
+// is understood by the Flutter framework. See the settings system channel for more
+// information.
+- (NSString*)brightnessMode {
+  if (@available(iOS 13, *)) {
+    UIUserInterfaceStyle style = self.traitCollection.userInterfaceStyle;
+
+    if (style == UIUserInterfaceStyleDark) {
+      return @"dark";
+    } else {
+      return @"light";
+    }
+  } else {
+    return @"light";
+  }
+}
+
+// The contrast mode of the platform, e.g., normal or high, expressed as a string that is
+// understood by the Flutter framework. See the settings system channel for more
+// information.
+- (NSString*)contrastMode {
+  if (@available(iOS 13, *)) {
+    UIAccessibilityContrast contrast = self.traitCollection.accessibilityContrast;
+
+    if (contrast == UIAccessibilityContrastHigh) {
+      return @"high";
+    } else {
+      return @"normal";
+    }
+  } else {
+    return @"normal";
+  }
+}
+
 #pragma mark - Status Bar touch event handling
 
 // Standard iOS status bar height in pixels.

shell/platform/darwin/ios/framework/Source/FlutterViewControllerTest.m

@@ -6,9 +6,29 @@
 #import <XCTest/XCTest.h>
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
 
+#include "FlutterBinaryMessenger.h"
+
+#if !__has_feature(objc_arc)
+#error ARC must be enabled!
+#endif
+
 @interface FlutterViewControllerTest : XCTestCase
 @end
 
+// The following conditional compilation defines an API 13 concept on earlier API targets so that
+// a compiler compiling against API 12 or below does not blow up due to non-existent members.
+#if __IPHONE_OS_VERSION_MAX_ALLOWED < 130000
+typedef enum UIAccessibilityContrast : NSInteger {
+  UIAccessibilityContrastUnspecified = 0,
+  UIAccessibilityContrastNormal = 1,
+  UIAccessibilityContrastHigh = 2
+} UIAccessibilityContrast;
+
+@interface UITraitCollection (MethodsFromNewerSDK)
+- (UIAccessibilityContrast)accessibilityContrast;
+@end
+#endif
+
 @implementation FlutterViewControllerTest
 
 - (void)testBinaryMessenger {
@@ -23,4 +43,205 @@ - (void)testBinaryMessenger {
   OCMVerify([engine binaryMessenger]);
 }
 
+#pragma mark - Platform Brightness
+
+- (void)testItReportsLightPlatformBrightnessByDefault {
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* vc = [[FlutterViewController alloc] initWithEngine:engine
+                                                                    nibName:nil
+                                                                     bundle:nil];
+
+  // Exercise behavior under test.
+  [vc traitCollectionDidChange:nil];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformBrightness"] isEqualToString:@"light"];
+                             }]]);
+
+  // Clean up mocks
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+}
+
+- (void)testItReportsPlatformBrightnessWhenViewWillAppear {
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* vc = [[FlutterViewController alloc] initWithEngine:engine
+                                                                    nibName:nil
+                                                                     bundle:nil];
+
+  // Exercise behavior under test.
+  [vc viewWillAppear:false];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformBrightness"] isEqualToString:@"light"];
+                             }]]);
+
+  // Clean up mocks
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+}
+
+- (void)testItReportsDarkPlatformBrightnessWhenTraitCollectionRequestsIt {
+  if (!@available(iOS 13, *)) {
+    return;
+  }
+
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* realVC = [[FlutterViewController alloc] initWithEngine:engine
+                                                                        nibName:nil
+                                                                         bundle:nil];
+  id mockTraitCollection =
+      [self fakeTraitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleDark];
+
+  // We partially mock the real FlutterViewController to act as the OS and report
+  // the UITraitCollection of our choice. Mocking the object under test is not
+  // desirable, but given that the OS does not offer a DI approach to providing
+  // our own UITraitCollection, this seems to be the least bad option.
+  id partialMockVC = OCMPartialMock(realVC);
+  OCMStub([partialMockVC traitCollection]).andReturn(mockTraitCollection);
+
+  // Exercise behavior under test.
+  [partialMockVC traitCollectionDidChange:nil];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformBrightness"] isEqualToString:@"dark"];
+                             }]]);
+
+  // Clean up mocks
+  [partialMockVC stopMocking];
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+  [mockTraitCollection stopMocking];
+}
+
+// Creates a mocked UITraitCollection with nil values for everything except userInterfaceStyle,
+// which is set to the given "style".
+- (UITraitCollection*)fakeTraitCollectionWithUserInterfaceStyle:(UIUserInterfaceStyle)style {
+  id mockTraitCollection = OCMClassMock([UITraitCollection class]);
+  OCMStub([mockTraitCollection userInterfaceStyle]).andReturn(style);
+  return mockTraitCollection;
+}
+
+#pragma mark - Platform Contrast
+
+- (void)testItReportsNormalPlatformContrastByDefault {
+  if (!@available(iOS 13, *)) {
+    return;
+  }
+
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* vc = [[FlutterViewController alloc] initWithEngine:engine
+                                                                    nibName:nil
+                                                                     bundle:nil];
+
+  // Exercise behavior under test.
+  [vc traitCollectionDidChange:nil];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformContrast"] isEqualToString:@"normal"];
+                             }]]);
+
+  // Clean up mocks
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+}
+
+- (void)testItReportsPlatformContrastWhenViewWillAppear {
+  if (!@available(iOS 13, *)) {
+    return;
+  }
+
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* vc = [[FlutterViewController alloc] initWithEngine:engine
+                                                                    nibName:nil
+                                                                     bundle:nil];
+
+  // Exercise behavior under test.
+  [vc viewWillAppear:false];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformContrast"] isEqualToString:@"normal"];
+                             }]]);
+
+  // Clean up mocks
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+}
+
+- (void)testItReportsHighContrastWhenTraitCollectionRequestsIt {
+  if (!@available(iOS 13, *)) {
+    return;
+  }
+
+  // Setup test.
+  id engine = OCMClassMock([FlutterEngine class]);
+
+  id settingsChannel = OCMClassMock([FlutterBasicMessageChannel class]);
+  OCMStub([engine settingsChannel]).andReturn(settingsChannel);
+
+  FlutterViewController* realVC = [[FlutterViewController alloc] initWithEngine:engine
+                                                                        nibName:nil
+                                                                         bundle:nil];
+  id mockTraitCollection = [self fakeTraitCollectionWithContrast:UIAccessibilityContrastHigh];
+
+  // We partially mock the real FlutterViewController to act as the OS and report
+  // the UITraitCollection of our choice. Mocking the object under test is not
+  // desirable, but given that the OS does not offer a DI approach to providing
+  // our own UITraitCollection, this seems to be the least bad option.
+  id partialMockVC = OCMPartialMock(realVC);
+  OCMStub([partialMockVC traitCollection]).andReturn(mockTraitCollection);
+
+  // Exercise behavior under test.
+  [partialMockVC traitCollectionDidChange:mockTraitCollection];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformContrast"] isEqualToString:@"high"];
+                             }]]);
+
+  // Clean up mocks
+  [partialMockVC stopMocking];
+  [engine stopMocking];
+  [settingsChannel stopMocking];
+  [mockTraitCollection stopMocking];
+}
+
+// Creates a mocked UITraitCollection with nil values for everything except accessibilityContrast,
+// which is set to the given "contrast".
+- (UITraitCollection*)fakeTraitCollectionWithContrast:(UIAccessibilityContrast)contrast {
+  id mockTraitCollection = OCMClassMock([UITraitCollection class]);
+  OCMStub([mockTraitCollection accessibilityContrast]).andReturn(contrast);
+  return mockTraitCollection;
+}
+
 @end

testing/ios/IosUnitTests/IosUnitTests.xcodeproj/project.pbxproj

@@ -7,7 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
-		0D17A5C022D78FCD0057279F /* FlutterViewControllerTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 0D17A5BF22D78FCD0057279F /* FlutterViewControllerTest.m */; };
+		0D17A5C022D78FCD0057279F /* FlutterViewControllerTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 0D17A5BF22D78FCD0057279F /* FlutterViewControllerTest.m */; settings = {COMPILER_FLAGS = "-fobjc-arc"; }; };
 		0D4C3FB022DF9F5300A67C70 /* FlutterPluginAppLifeCycleDelegateTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 0D4C3FAF22DF9F5300A67C70 /* FlutterPluginAppLifeCycleDelegateTest.m */; settings = {COMPILER_FLAGS = "-fobjc-arc"; }; };
 		0D52D3BD22C566D50011DEBD /* FlutterBinaryMessengerRelayTest.mm in Sources */ = {isa = PBXBuildFile; fileRef = 0D52D3B622C566D50011DEBD /* FlutterBinaryMessengerRelayTest.mm */; settings = {COMPILER_FLAGS = "-fobjc-arc"; }; };
 		0D6AB6B622BB05E100EEE540 /* AppDelegate.m in Sources */ = {isa = PBXBuildFile; fileRef = 0D6AB6B522BB05E100EEE540 /* AppDelegate.m */; };