对接低功耗中心蓝牙设备，notifyBLECharacteristicValueChange成功，writeBLECharacteristicValue也是成功，但是无法接受设备返回数据，onBLECharacteristicValueChange

 lanyatest10(event){

      var that = this;

      console.log("开始接收数据");

      function ab2hex(buffer) {

        let hexArr = Array.prototype.map.call(

          new Uint8Array(buffer),

          function(bit) {

            return ('00' + bit.toString(16)).slice(-2)

          }

        )

        return hexArr.join('');

      }

      wx.onBLECharacteristicValueChange(function (res) {

        console.log("characteristicId：" + res.characteristicId)

        console.log("serviceId:" + res.serviceId)

        console.log("deviceId" + res.deviceId)

        console.log("Length:" + res.value.byteLength)

        console.log("hexvalue:" + ab2hex(res.value))

        that.setData({

          info: that.data.info + ab2hex(res.value)

        })

      })

    },