iOS Allow disabling color scheme preference

Summary:
Some apps may need to disable the automatic dark mode color scheme assignment. This provides such kill switch.

Changelog: [Internal]

Reviewed By: yungsters

Differential Revision: D18088313

fbshipit-source-id: 75abf34e92f8a4a637daa26135adf85965cb9df5

React/CoreModules/RCTAppearance.h

@@ -10,6 +10,8 @@
 #import <React/RCTBridgeModule.h>
 #import <React/RCTEventEmitter.h>
 
+RCT_EXTERN void RCTEnableAppearancePreference(BOOL enabled);
+
 NSString *const RCTUserInterfaceStyleDidChangeNotification = @"RCTUserInterfaceStyleDidChangeNotification";
 
 @interface RCTAppearance : RCTEventEmitter <RCTBridgeModule>

React/CoreModules/RCTAppearance.mm

@@ -17,6 +17,11 @@
 NSString *const RCTAppearanceColorSchemeLight = @"light";
 NSString *const RCTAppearanceColorSchemeDark = @"dark";
 
+static BOOL sAppearancePreferenceEnabled = YES;
+void RCTEnableAppearancePreference(BOOL enabled) {
+ sAppearancePreferenceEnabled = enabled;
+}
+
 static NSString *RCTColorSchemePreference(UITraitCollection *traitCollection)
 {
 #if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_13_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_13_0
@@ -31,6 +36,11 @@
  };
  });
 
+ if (!sAppearancePreferenceEnabled) {
+ // Return the default if the app doesn't allow different color schemes.
+ return RCTAppearanceColorSchemeLight;
+ }
+
  traitCollection = traitCollection ?: [UITraitCollection currentTraitCollection];
  return appearances[@(traitCollection.userInterfaceStyle)] ?: RCTAppearanceColorSchemeLight;
  }