Add useScreenDimensions hook

packages/react-native/Libraries/Utilities/__tests__/useScreenDimensions-test.js

@@ -0,0 +1,103 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+import type {ReactTestRenderer} from 'react-test-renderer';
+
+import Dimensions from '../Dimensions';
+import useScreenDimensions from '../useScreenDimensions';
+import {create, unmount} from '@react-native/jest-preset/jest/renderer';
+import * as React from 'react';
+import {act} from 'react-test-renderer';
+
+describe('useScreenDimensions', () => {
+  const window = {width: 320, height: 480, scale: 2, fontScale: 1};
+  const screen = {width: 400, height: 800, scale: 2, fontScale: 1};
+  let renderer: ?ReactTestRenderer;
+  let observed;
+  let renderCount;
+  let originalDimensions;
+
+  function TestComponent() {
+    observed = useScreenDimensions();
+    renderCount++;
+    return null;
+  }
+
+  beforeEach(() => {
+    originalDimensions = {
+      window: Dimensions.get('window'),
+      screen: Dimensions.get('screen'),
+    };
+    Dimensions.set({window, screen});
+    renderCount = 0;
+  });
+
+  afterEach(async () => {
+    if (renderer != null) {
+      await unmount(renderer);
+      renderer = null;
+    }
+    jest.restoreAllMocks();
+    Dimensions.set(originalDimensions);
+  });
+
+  it('returns screen metrics rather than window metrics', async () => {
+    renderer = await create(<TestComponent />);
+    expect(observed).toEqual(screen);
+    expect(observed).not.toEqual(window);
+  });
+
+  it.each([
+    ['width', 800],
+    ['height', 400],
+    ['scale', 3],
+    ['fontScale', 1.5],
+  ])('updates when %s changes', async (property, value) => {
+    renderer = await create(<TestComponent />);
+    const nextScreen = {...screen, [property]: value};
+    await act(() => {
+      Dimensions.set({window, screen: nextScreen});
+    });
+    expect(observed).toEqual(nextScreen);
+  });
+
+  it('does not render again for window-only changes or identical screen metrics', async () => {
+    renderer = await create(<TestComponent />);
+    const previousRenderCount = renderCount;
+    const previousDimensions = observed;
+    await act(() => {
+      Dimensions.set({window: {...window, width: 200}, screen: {...screen}});
+    });
+    expect(renderCount).toBe(previousRenderCount);
+    expect(observed).toBe(previousDimensions);
+  });
+
+  it('catches changes between render and subscription', async () => {
+    const nextScreen = {...screen, width: 800, height: 400};
+    function UpdateBeforeSubscription() {
+      React.useLayoutEffect(() => {
+        Dimensions.set({window, screen: nextScreen});
+      }, []);
+      return <TestComponent />;
+    }
+    renderer = await create(<UpdateBeforeSubscription />);
+    expect(observed).toEqual(nextScreen);
+  });
+
+  it('removes its subscription on unmount', async () => {
+    const addEventListener = jest.spyOn(Dimensions, 'addEventListener');
+    renderer = await create(<TestComponent />);
+    const subscription = addEventListener.mock.results[0].value;
+    const remove = jest.spyOn(subscription, 'remove');
+    await unmount(renderer);
+    renderer = null;
+    expect(remove).toHaveBeenCalledTimes(1);
+  });
+});

packages/react-native/Libraries/Utilities/useScreenDimensions.js

@@ -0,0 +1,53 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+import Dimensions from './Dimensions';
+import {
+  type DisplayMetrics,
+  type DisplayMetricsAndroid,
+} from './NativeDeviceInfo';
+import {useEffect, useState} from 'react';
+
+/**
+ * React hook that provides the screen's width, height, scale, and
+ * font scale. Automatically updates when screen size or font scale changes.
+ *
+ * Width and height are reported in logical pixels, as in `Dimensions.get('screen')`.
+ */
+export default function useScreenDimensions():
+  DisplayMetrics | DisplayMetricsAndroid {
+  const [dimensions, setDimensions] = useState(() => Dimensions.get('screen'));
+  useEffect(() => {
+    function handleChange({
+      screen,
+    }: Readonly<{
+      screen: DisplayMetrics | DisplayMetricsAndroid,
+      ...
+    }>) {
+      if (
+        dimensions.width !== screen.width ||
+        dimensions.height !== screen.height ||
+        dimensions.scale !== screen.scale ||
+        dimensions.fontScale !== screen.fontScale
+      ) {
+        setDimensions(screen);
+      }
+    }
+    const subscription = Dimensions.addEventListener('change', handleChange);
+    // We might have missed an update between calling `get` in render and
+    // `addEventListener` in this handler, so we set it here. If there was
+    // no change, React will filter out this update as a no-op.
+    handleChange({screen: Dimensions.get('screen')});
+    return () => {
+      subscription.remove();
+    };
+  }, [dimensions]);
+  return dimensions;
+}

packages/react-native/ReactNativeApi.d.ts

@@ -5433,6 +5433,7 @@ declare function useColorScheme(): ColorSchemeName | null
 declare function usePressability(
   config: null | PressabilityConfig | undefined,
 ): null | PressabilityEventHandlers
+declare function useScreenDimensions(): DisplayMetrics | DisplayMetricsAndroid
 declare function useWindowDimensions(): DisplayMetrics | DisplayMetricsAndroid
 declare type UTFSequence = typeof UTFSequence
 declare type Value = null | {
@@ -6065,5 +6066,6 @@ export {
   useAnimatedValueXY, // dc9057ea
   useColorScheme, // d585efdb
   usePressability, // af291ad3
+  useScreenDimensions, // a8bd8ad8
   useWindowDimensions, // bb4b683f
 }

packages/react-native/__typetests__/index.tsx

@@ -121,6 +121,7 @@ import {
   requireNativeComponent,
   useColorScheme,
   useWindowDimensions,
+  useScreenDimensions,
   // @ts-ignore
   SectionListData,
   ToastAndroid,
@@ -165,6 +166,11 @@ function testDimensions() {
   subscription.remove();
 }
 
+function TestUseScreenDimensions() {
+  const {width, height, scale, fontScale} = useScreenDimensions();
+  const metrics: number[] = [width, height, scale, fontScale];
+}
+
 function TextUseWindowDimensions() {
   const {width, height, scale, fontScale} = useWindowDimensions();
 }

packages/react-native/index.js

@@ -389,6 +389,9 @@ module.exports = {
   get usePressability() {
     return require('./Libraries/Pressability/usePressability').default;
   },
+  get useScreenDimensions() {
+    return require('./Libraries/Utilities/useScreenDimensions').default;
+  },
   get useWindowDimensions() {
     return require('./Libraries/Utilities/useWindowDimensions').default;
   },

packages/react-native/index.js.flow

@@ -460,6 +460,7 @@ export type {
 } from './Libraries/Pressability/Pressability';
 export {default as usePressability} from './Libraries/Pressability/usePressability';
 export {default as useColorScheme} from './Libraries/Utilities/useColorScheme';
+export {default as useScreenDimensions} from './Libraries/Utilities/useScreenDimensions';
 export {default as useWindowDimensions} from './Libraries/Utilities/useWindowDimensions';
 export {default as UTFSequence} from './Libraries/UTFSequence';
 export {default as Vibration} from './Libraries/Vibration/Vibration';

packages/react-native/types_DEPRECATED/Libraries/Utilities/Dimensions.d.ts

@@ -76,4 +76,7 @@ export interface Dimensions {
 
 export function useWindowDimensions(): ScaledSize;
 
+/** Returns screen dimensions and updates when they change. */
+export function useScreenDimensions(): ScaledSize;
+
 export const Dimensions: Dimensions;