问题描述：

音乐播放过程中，切换到应用其他页面时，用后台的状态栏切换音乐时音乐会暂停。

问题分析：

华为audio接口只能在页面中使用，当audio所在的页面退出后，页面销毁，绑定的上下文对象也随之不存在。此时，在通知栏上一首、下一首切换歌曲时，后台播放服务首先暂停当前歌曲，状态重置，但是audio接口的绑定事件找不到上下文对象，无法触发previous和next事件，导致上述现象。

解决方案:

在应用首页监听audio事件，而不仅仅是在播放页面添加，当用户离开播放页面时，依然可以监听到audio的每个事件，从而去控制播放逻辑。

注意：由于华为快应用引擎不支持在app.ux里调用audio接口，所以当用户退出了整个应用，虽然后台依然在播放，但是快应用是不能收到audio的事件回调的。

实现代码：

以下示例demo中有两个页面：首页Main和音频Audio。为了避免重复代码，可维护性，将audio的相关代码独立出来作为一个公共的js，方便每个页面调用。

1）公共utils.js：

import audio from '@system.audio';
export default{listenAudio() {var that=this;console.info("util.js listenAudio ");audio.onplay = function () {console.log('audio onplay')}audio.onpause = function () {console.log('audio onpause')}audio.onended = function () {console.log('audio onended')}audio.ondurationchange = function () {console.log('util.js ondurationchange')var total = audio.durationconsole.log('util.js ondurationchange total=' + total)}audio.ontimeupdate = function () {var time = audio.currentTime//  console.log('util.js ontimeupdate time=' + time)}audio.onprevious = function () {audio.cover = 'https://xx.jpg'audio.title = "钢琴曲"audio.artist = "莫扎特"// Replace with NetEase cloud music resource linkaudio.src = 'https://xx.mp3'console.log(' util.js on previout event from notification ')}audio.onnext = function () {audio.cover = 'xx.jpg'audio.title = '轻音乐';audio.artist = '王菲'// Replace with NetEase cloud music resource linkaudio.src = 'https://xx.mp3'console.log(' util.js on next event from notification ')}},getAudioPlayState() {audio.getPlayState({success: function (data) {console.log(`getAudioPlayState success: state: ${data.state},src:${data.src},currentTime:${data.currentTime},autoplay:${data.autoplay},loop:${data.loop},volume: ${data.volume},muted:${data.muted},notificationVisible:${data.notificationVisible}`);},fail: function (data, code) {console.log('getAudioPlayState fail, code=' + code);}});},startPlay() {audio.play();},pausePlay() {audio.pause();},stopPlay() {audio.stop();},seekProress(len) {audio.currentTime = len;},setVolume(value) {audio.volume = value;},setMute(isMuted) {audio.muted = isMuted},setLoop(isloop) {audio.loop = isloop},setStreamType() {if (audio.streamType === 'music') {audio.streamType = 'voicecall'} else {audio.streamType = 'music'}console.error('audio.streamType =' + audio.streamType);},setTitle(title) {console.info('setTitle=' + title);audio.title = title;},setArtist(artist) {console.info('setArtist artist=' + artist) ;audio.artist = artist;},setCover(src) {console.info('setCover src=' + src);  audio.cover = src;}
}

2）在首页Main的生命周期onShow方法中添加监听audio事件，调用utils.js中的listenAudio，代码如下：

<script>import utils from '../Util/utils.js';module.exports = {onShow(options) {utils.listenAudio();},}
</script>

在音频Audio页面生命周期onShow方法中添加监听audio事件，调用utils.js中的listenAudio，由于在播放页面需要显示播放进度，单独监听了进度回调事件，代码如下：

onShow(options) {var that = this;utils.listenAudio();audio.ondurationchange = function () {console.log('audio ondurationchange')that.total = audio.durationconsole.log('audio ondurationchange total=' + that.total)}audio.ontimeupdate = function () {that.time = audio.currentTimeconsole.log('ontimeupdate time=' + that.time)}},