Appearance.setColorScheme support (revisited) (#36122)

Summary:
Both Android and iOS allow you to set application specific user interface style, which is useful for applications that support both light and dark mode.

With the newly added `Appearance.setColorScheme`, you can natively manage the application's user interface style rather than keeping that preference in JavaScript. The benefit is that native dialogs like alert, keyboard, action sheets and more will also be affected by this change.

Implemented using Android X [AppCompatDelegate.setDefaultNightMode](https://developer.android.com/reference/androidx/appcompat/app/AppCompatDelegate#setDefaultNightMode(int)) and iOS 13+ [overrideUserInterfaceStyle](https://developer.apple.com/documentation/uikit/uiview/3238086-overrideuserinterfacestyle?language=objc)

```tsx
// Lets assume a given device is set to **dark** mode.

Appearance.getColorScheme(); // `dark`

// Set the app's user interface to `light`
Appearance.setColorScheme('light');

Appearance.getColorScheme(); // `light`

// Set the app's user interface to `unspecified`
Appearance.setColorScheme(null);

Appearance.getColorScheme() // `dark`
 ```

## Changelog

[GENERAL] [ADDED] - Added `setColorScheme` to `Appearance` module

Pull Request resolved: https://github.com/facebook/react-native/pull/36122

Test Plan:
Added a RNTester for the feature in the Appearance section.

Three buttons for toggling all set of modes.

Reviewed By: lunaleaps

Differential Revision: D43331405

Pulled By: NickGerleman

fbshipit-source-id: 3b15f1ed0626d1ad7a8266ec026e903cd3ec46aa

Libraries/Utilities/Appearance.d.ts

@@ -28,6 +28,16 @@ export namespace Appearance {
    */
   export function getColorScheme(): ColorSchemeName;
 
+  /**
+   * Set the color scheme preference. This is useful for overriding the default
+   * color scheme preference for the app. Note that this will not change the
+   * appearance of the system UI, only the appearance of the app.
+   * Only available on iOS 13+ and Android 10+.
+   */
+  export function setColorScheme(
+    scheme: ColorSchemeName | null | undefined,
+  ): void;
+
   /**
    * Add an event handler that is fired when appearance preferences change.
    */

Libraries/Utilities/Appearance.js

@@ -85,6 +85,19 @@ module.exports = {
     return nativeColorScheme;
   },
 
+  setColorScheme(colorScheme: ?ColorSchemeName): void {
+    const nativeColorScheme = colorScheme == null ? 'unspecified' : colorScheme;
+
+    invariant(
+      colorScheme === 'dark' || colorScheme === 'light' || colorScheme == null,
+      "Unrecognized color scheme. Did you mean 'dark', 'light' or null?",
+    );
+
+    if (NativeAppearance != null && NativeAppearance.setColorScheme != null) {
+      NativeAppearance.setColorScheme(nativeColorScheme);
+    }
+  },
+
   /**
    * Add an event handler that is fired when appearance preferences change.
    */

Libraries/Utilities/NativeAppearance.js

@@ -26,6 +26,7 @@ export interface Spec extends TurboModule {
   // types.
   /* 'light' | 'dark' */
   +getColorScheme: () => ?string;
+  +setColorScheme?: (colorScheme: string) => void;
 
   // RCTEventEmitter
   +addListener: (eventName: string) => void;

React/CoreModules/RCTAppearance.h

@@ -8,6 +8,7 @@
 #import <UIKit/UIKit.h>
 
 #import <React/RCTBridgeModule.h>
+#import <React/RCTConvert.h>
 #import <React/RCTEventEmitter.h>
 
 RCT_EXTERN void RCTEnableAppearancePreference(BOOL enabled);

React/CoreModules/RCTAppearance.mm

@@ -10,6 +10,7 @@
 #import <FBReactNativeSpec/FBReactNativeSpec.h>
 #import <React/RCTConstants.h>
 #import <React/RCTEventEmitter.h>
+#import <React/RCTUtils.h>
 
 #import "CoreModulesPlugins.h"
 
@@ -68,6 +69,20 @@ NSString *RCTColorSchemePreference(UITraitCollection *traitCollection)
   return RCTAppearanceColorSchemeLight;
 }
 
+@implementation RCTConvert (UIUserInterfaceStyle)
+
+RCT_ENUM_CONVERTER(
+    UIUserInterfaceStyle,
+    (@{
+      @"light" : @(UIUserInterfaceStyleLight),
+      @"dark" : @(UIUserInterfaceStyleDark),
+      @"unspecified" : @(UIUserInterfaceStyleUnspecified)
+    }),
+    UIUserInterfaceStyleUnspecified,
+    integerValue);
+
+@end
+
 @interface RCTAppearance () <NativeAppearanceSpec>
 @end
 
@@ -92,6 +107,17 @@ RCT_EXPORT_MODULE(Appearance)
   return std::make_shared<NativeAppearanceSpecJSI>(params);
 }
 
+RCT_EXPORT_METHOD(setColorScheme : (NSString *)style)
+{
+  UIUserInterfaceStyle userInterfaceStyle = [RCTConvert UIUserInterfaceStyle:style];
+  NSArray<__kindof UIWindow *> *windows = RCTSharedApplication().windows;
+  if (@available(iOS 13.0, *)) {
+    for (UIWindow *window in windows) {
+      window.overrideUserInterfaceStyle = userInterfaceStyle;
+    }
+  }
+}
+
 RCT_EXPORT_SYNCHRONOUS_TYPED_METHOD(NSString *, getColorScheme)
 {
   if (_currentColorScheme == nil) {

ReactAndroid/src/main/java/com/facebook/react/modules/appearance/AppearanceModule.java

@@ -11,6 +11,7 @@ import android.app.Activity;
 import android.content.Context;
 import android.content.res.Configuration;
 import androidx.annotation.Nullable;
+import androidx.appcompat.app.AppCompatDelegate;
 import com.facebook.fbreact.specs.NativeAppearanceSpec;
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.ReactApplicationContext;
@@ -65,6 +66,17 @@ public class AppearanceModule extends NativeAppearanceSpec {
     return "light";
   }
 
+  @Override
+  public void setColorScheme(String style) {
+    if (style.equals("dark")) {
+      AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
+    } else if (style.equals("light")) {
+      AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
+    } else if (style.equals("unspecified")) {
+      AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
+    }
+  }
+
   @Override
   public String getColorScheme() {
     // Attempt to use the Activity context first in order to get the most up to date

ReactAndroid/src/main/java/com/facebook/react/modules/appearance/BUCK

@@ -14,6 +14,7 @@ rn_android_library(
     deps = [
         react_native_dep("third-party/java/jsr-305:jsr-305"),
         react_native_dep("third-party/android/androidx:annotation"),
+        react_native_dep("third-party/android/androidx:appcompat"),
         react_native_target("java/com/facebook/react/bridge:bridge"),
         react_native_target("java/com/facebook/react/common:common"),
         react_native_target("java/com/facebook/react/module/annotations:annotations"),

ReactAndroid/src/main/java/com/facebook/react/shell/BUCK

@@ -15,6 +15,7 @@ rn_android_library(
         react_native_dep("libraries/fresco/fresco-react-native:imagepipeline"),
         react_native_dep("libraries/soloader/java/com/facebook/soloader:soloader"),
         react_native_dep("third-party/android/androidx:annotation"),
+        react_native_dep("third-party/android/androidx:appcompat"),
         react_native_dep("third-party/android/androidx:core"),
         react_native_dep("third-party/android/androidx:fragment"),
         react_native_dep("third-party/android/androidx:legacy-support-core-utils"),

packages/rn-tester/js/examples/Appearance/AppearanceExample.js

@@ -10,7 +10,7 @@
 
 import * as React from 'react';
 import {useState, useEffect} from 'react';
-import {Appearance, Text, useColorScheme, View} from 'react-native';
+import {Appearance, Text, useColorScheme, View, Button} from 'react-native';
 import type {
   AppearancePreferences,
   ColorSchemeName,
@@ -135,6 +135,32 @@ const ColorShowcase = (props: {themeName: string}) => (
   </RNTesterThemeContext.Consumer>
 );
 
+const ToggleNativeAppearance = () => {
+  const [nativeColorScheme, setNativeColorScheme] =
+    useState<ColorSchemeName | null>(null);
+  const colorScheme = useColorScheme();
+
+  useEffect(() => {
+    Appearance.setColorScheme(nativeColorScheme);
+  }, [nativeColorScheme]);
+
+  return (
+    <View>
+      <Text>Native colorScheme: {nativeColorScheme}</Text>
+      <Text>Current colorScheme: {colorScheme}</Text>
+      <Button
+        title="Set to light"
+        onPress={() => setNativeColorScheme('light')}
+      />
+      <Button
+        title="Set to dark"
+        onPress={() => setNativeColorScheme('dark')}
+      />
+      <Button title="Unset" onPress={() => setNativeColorScheme(null)} />
+    </View>
+  );
+};
+
 exports.title = 'Appearance';
 exports.category = 'UI';
 exports.documentationURL = 'https://reactnative.dev/docs/appearance';
@@ -214,4 +240,11 @@ exports.examples = [
       );
     },
   },
+  {
+    title: 'Toggle native appearance',
+    description: 'Overwrite application-level appearance mode',
+    render(): React.Element<any> {
+      return <ToggleNativeAppearance />;
+    },
+  },
 ];