用React Native做一个填字游戏（4）——监听程序状态

当我们的程序在前后台直接做切换时，有时需要一些必要的动作，如暂停背景音乐、保存用户输入等。在Android上，我们使用的是onPause和onResume，RN提供AppState来监听APP的状态，简略使用方法如下，具体的API文档参见AppState

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

  _handleAppStateChange(nextAppState) {
    const { appState, backgroundMusic } = this.state;
    if (appState.match(/inactive|background/) && nextAppState === 'active') {
      if (backgroundMusic) {
        backgroundMusic.play();
      } else {
        this._playBackgroundMusic();
      }
    } else if (appState === 'active' && nextAppState.match(/inactive|background/)) {
      if (backgroundMusic) {
        backgroundMusic.pause();
      }
    }
    this.setState({appState: nextAppState});
  }

  componentDidMount() {
    AppState.addEventListener('change', this._handleAppStateChange);
  }

  componentWillUnmount() {
    AppState.removeEventListener('change', this._handleAppStateChange);
  }