明明存在此特性,onBLECharacteristicValueChange却不执行

notifyBLECharacteristicValue() {
		let _this = this;
		let deviceId = _this.deviceId;
		let serviceId = _this.serviceId;
		let characteristicId = _this.notifyId;
		console.log(characteristicId, 'characteristicId');
		return new Promise((resolve, reject) => {
			uni.notifyBLECharacteristicValueChange({
				state: true, // 启用 notify 功能
				deviceId,
				serviceId,
				characteristicId,
				success(res) {
					resolve(res);
					console.log(res, 'success');
					uni.onBLECharacteristicValueChange(function(res) {
						console.log('特征值变化', res);
					})
					uni.onBLEConnectionStateChange(function(res) {
					  // 该方法回调中可以用于处理连接意外断开等异常情况
					  console.log('蓝牙状态', res)
					})
				},
				fail(err) {
					console.log(err, 'fail');
					_this.showToast('该蓝牙设备不支持打印')
					reject(err);
				}
			});
		})
	}