wx.notifyBLECharacteristicValueChange({             state: true,              deviceId,             serviceId,             characteristicId,             success (res) {               console.log("readStepByFive->成功:"+JSON.stringify(res))               wx.onBLECharacteristicValueChange(function(characteristic) {                 console.log("你好");                 console.log('characteristic value comed:', characteristic)               })             },             fail(res){               console.log("readStepByFive->失败:"+JSON.stringify(res));               that.readHRFail("读取失败");             }           }) 对我司的一个传感器notify之后，传感器会把自身的内存数据源源传送给我(Android原生端已经实现了)。在小程序,调用了wx.notifyBLECharacteristicValueChange之后，回调了success方法，数据如下{"errno":0,"errCode":0,"errMsg":"notifyBLECharacteristicValueChange:ok"}。但是wx.onBLECharacteristicValueChange却没有源源不但返回数据是为什么呢？