RN: Change Appearance to Return EventSubscription

Summary:
Changes `Appearance.addChangeListener` to return an `EventSubscription` object that has a `remove()` method on it.

In an upcoming commit, calling `Appearance.removeChangeListener` will lead to a deprecation warning.

Changelog:
[General][Change] - `Appearance.addChangeListener` now returns an `EventSubscription`.

Reviewed By: kacieb

Differential Revision: D26696388

fbshipit-source-id: d0bdeffff3a2a366b3c11b6dc1417dfb2f1455c2

Author: yungsters

Libraries/Utilities/Appearance.js

@@ -8,7 +8,9 @@
  * @flow strict-local
  */
 
-import EventEmitter from '../vendor/emitter/EventEmitter';
+import EventEmitter, {
+  type EventSubscription,
+} from '../vendor/emitter/EventEmitter';
 import NativeEventEmitter from '../EventEmitter/NativeEventEmitter';
 import NativeAppearance, {
   type AppearancePreferences,
@@ -78,16 +80,19 @@ module.exports = {
     );
     return nativeColorScheme;
   },
+
   /**
    * Add an event handler that is fired when appearance preferences change.
    */
-  addChangeListener(listener: AppearanceListener): void {
-    eventEmitter.addListener('change', listener);
+  addChangeListener(listener: AppearanceListener): EventSubscription {
+    return eventEmitter.addListener('change', listener);
   },
+
   /**
-   * Remove an event handler.
+   * @deprecated Use `remove` on the EventSubscription from `addEventListener`.
    */
   removeChangeListener(listener: AppearanceListener): void {
+    // NOTE: This will report a deprecation notice via `console.error`.
     eventEmitter.removeListener('change', listener);
   },
 };

Libraries/Utilities/useColorScheme.js

@@ -18,8 +18,10 @@ export default function useColorScheme(): ?ColorSchemeName {
     () => ({
       getCurrentValue: () => Appearance.getColorScheme(),
       subscribe: callback => {
-        Appearance.addChangeListener(callback);
-        return () => Appearance.removeChangeListener(callback);
+        const appearanceSubscription = Appearance.addChangeListener(callback);
+        return () => {
+          appearanceSubscription.remove();
+        };
       },
     }),
     [],

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

@@ -11,29 +11,32 @@
 import * as React from 'react';
 import {Appearance, Text, useColorScheme, View} from 'react-native';
 import type {AppearancePreferences} from 'react-native/Libraries/Utilities/NativeAppearance';
+import type {EventSubscription} from 'react-native/Libraries/vendor/emitter/EventEmitter';
 import {RNTesterThemeContext, themes} from '../../components/RNTesterTheme';
 
 class ColorSchemeSubscription extends React.Component<
   {...},
   {colorScheme: ?string, ...},
 > {
+  _subscription: ?EventSubscription;
+
   state = {
     colorScheme: Appearance.getColorScheme(),
   };
 
   componentDidMount() {
-    Appearance.addChangeListener(this._handleAppearanceChange);
+    this._subscription = Appearance.addChangeListener(
+      (preferences: AppearancePreferences) => {
+        const {colorScheme} = preferences;
+        this.setState({colorScheme});
+      },
+    );
   }
 
   componentWillUnmount() {
-    Appearance.removeChangeListener(this._handleAppearanceChange);
+    this._subscription?.remove();
   }
 
-  _handleAppearanceChange = (preferences: AppearancePreferences) => {
-    const {colorScheme} = preferences;
-    this.setState({colorScheme});
-  };
-
   render() {
     return (
       <RNTesterThemeContext.Consumer>