Forwards iOS dark mode trait to the Flutter framework (#34441). (flutter/engine#9722)

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -681,6 +681,11 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
   [_engine.get() updateViewportMetrics:_viewportMetrics];
 }
 
+- (void)updateViewConstraints {
+  [super updateViewConstraints];
+  [self onUserSettingsChanged:nil];
+}
+
 - (CGFloat)statusBarPadding {
   UIScreen* screen = self.view.window.screen;
   CGRect statusFrame = [UIApplication sharedApplication].statusBarFrame;
@@ -690,6 +695,11 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
   return CGRectIsNull(intersection) ? 0.0 : intersection.size.height;
 }
 
+- (void)viewWillLayoutSubviews {
+  [super viewWillLayoutSubviews];
+  [self onUserSettingsChanged:nil];
+}
+
 - (void)viewDidLayoutSubviews {
   CGSize viewSize = self.view.bounds.size;
   CGFloat scale = [UIScreen mainScreen].scale;
@@ -702,6 +712,7 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
 
   [self updateViewportPadding];
   [self updateViewportMetrics];
+  [self onUserSettingsChanged:nil];
 
   // This must run after updateViewportMetrics so that the surface creation tasks are queued after
   // the viewport metrics update tasks.
@@ -863,10 +874,16 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
 
 #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]
   }];
 }
 
@@ -940,6 +957,20 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
   return [dateFormat rangeOfString:@"a"].location == NSNotFound;
 }
 
+- (NSString*)brightnessMode {
+  if (@available(iOS 13, *)) {
+    UIUserInterfaceStyle style = UITraitCollection.currentTraitCollection.userInterfaceStyle;
+
+    if (style == UIUserInterfaceStyleDark) {
+      return @"dark";
+    } else {
+      return @"light";
+    }
+  } else {
+    return @"light";
+  }
+}
+
 #pragma mark - Status Bar touch event handling
 
 // Standard iOS status bar height in pixels.

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewControllerTest.m

@@ -6,6 +6,8 @@
 #import <XCTest/XCTest.h>
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
 
+#include "FlutterBinaryMessenger.h"
+
 @interface FlutterViewControllerTest : XCTestCase
 @end
 
@@ -23,4 +25,85 @@
   OCMVerify([engine binaryMessenger]);
 }
 
+- (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"];
+                             }]]);
+}
+
+- (void)testItReportsDarkPlatformBrightnessWhenTraitCollectionRequestsIt {
+  // 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];
+  id mockTraitCollection = [self setupFakeUserInterfaceStyle:UIUserInterfaceStyleDark];
+
+  // Exercise behavior under test.
+  [vc traitCollectionDidChange:nil];
+
+  // Verify behavior.
+  OCMVerify([settingsChannel sendMessage:[OCMArg checkWithBlock:^BOOL(id message) {
+                               return [message[@"platformBrightness"] isEqualToString:@"light"];
+                             }]]);
+
+  // Restore UIUserInterfaceStyle
+  [mockTraitCollection stopMocking];
+}
+
+- (void)testItReportsPlatformBrightnessWhenExpected {
+  // 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];
+  id mockTraitCollection = [self setupFakeUserInterfaceStyle:UIUserInterfaceStyleDark];
+
+  __block int messageCount = 0;
+  OCMStub([settingsChannel sendMessage:[OCMArg any]]).andDo(^(NSInvocation* invocation) {
+    messageCount = messageCount + 1;
+  });
+
+  // Exercise behavior under test.
+  [vc updateViewConstraints];
+  [vc viewWillLayoutSubviews];
+  [vc traitCollectionDidChange:nil];
+  [vc onUserSettingsChanged:nil];
+
+  // Verify behavior.
+  XCTAssertEqual(messageCount, 4);
+
+  // Restore UIUserInterfaceStyle
+  [mockTraitCollection stopMocking];
+}
+
+- (UITraitCollection*)setupFakeUserInterfaceStyle:(UIUserInterfaceStyle)style {
+  id mockTraitCollection = OCMClassMock([UITraitCollection class]);
+  OCMStub([mockTraitCollection userInterfaceStyle]).andReturn(UIUserInterfaceStyleDark);
+  OCMStub([mockTraitCollection currentTraitCollection]).andReturn(mockTraitCollection);
+  return mockTraitCollection;
+}
+
 @end

engine/src/flutter/testing/ios/IosUnitTests/run_tests.sh

@@ -12,6 +12,6 @@ fi
 
 set -o pipefail && xcodebuild -sdk iphonesimulator \
   -scheme IosUnitTests \
-  -destination 'platform=iOS Simulator,name=iPhone SE,OS=12.2' \
+  -destination 'platform=iOS Simulator,name=iPhone 8,OS=13.0' \
   test \
   FLUTTER_ENGINE=$FLUTTER_ENGINE | $PRETTY