react-native/Libraries/Utilities/useWindowDimensions.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @format
 * @flow strict-local
 */

import Dimensions from './Dimensions';
import {type DisplayMetrics} from './NativeDeviceInfo';
import {useEffect, useState} from 'react';

export default function useWindowDimensions(): DisplayMetrics {
  const [dimensions, setDimensions] = useState(() => Dimensions.get('window'));
  useEffect(() => {
    function handleChange({window}) {
      if (
        dimensions.width !== window.width ||
        dimensions.height !== window.height ||
        dimensions.scale !== window.scale ||
        dimensions.fontScale !== window.fontScale
      ) {
        setDimensions(window);
      }
    }
    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({window: Dimensions.get('window')});
    return () => {
      Dimensions.removeEventListener('change', handleChange);
    };
  }, [dimensions]);
  return dimensions;
}