这样导致回显给用户的播放时间计时器 Interval 无法在音频播放完成后清除，体验上有些不足。

playVoice:function (idx) {

    let that = this;
    this.data.playTime = 0;

    playInterval = setInterval(function () {
        that.data.playTime ++;
        that.data.playTimeFormat = Utils.formatTime(that.data.playTime);
        that.setData(that.data)
    },1000);

    wx.playVoice({
        filePath:that.data.voiceList[idx].voice,
        success:function () {
            that.setData({playing:false,playIdx:-1});
            clearInterval(playInterval);
        },
        complete:function () {
            clearInterval(playInterval);
        }
    })
},