react-native-google-mobile-ads/lib/module/hooks/useForeground.js

React Native Google Mobile Ads is an easy way to monetize mobile apps with targeted, in-app advertising.

/*
 * Copyright (c) 2016-present Invertase Limited & Contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this library except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

import { useEffect, useRef } from 'react';
import { AppState } from 'react-native';

/**
 * A custom hook that invokes a callback when the app transitions to the foreground.
 *
 * @param {Function} callback - The function to be called when the app has come to the foreground.
 */
export function useForeground(callback) {
  const appState = useRef(AppState.currentState);
  useEffect(() => {
    const subscription = AppState.addEventListener('change', nextAppState => {
      if (appState.current === 'background' && nextAppState === 'active') {
        callback();
      }
      appState.current = nextAppState;
    });
    return () => {
      subscription.remove();
    };
  }, []);
}
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