假设手表扩展中存在xishuai.mp3文件。

let url = Bundle.main.url(forResource: "xishuai", withExtension: "mp3")!
let playAsset = WKAudioFileAsset(url: url)
let playItem = WKAudioFilePlayerItem(asset: playAsset)
player = WKAudioFilePlayer(playerItem: playItem)

WKAudioFilePlayer目前在真机下，如果真机没有连接蓝牙耳机，则播放无声音。因此，不能保证作为通知声音的替代。