Web BLE 特性 startNotifications 有时不绑定

Question

我正在使用网络 BLE。我根据心率测量的例子编写了我的代码。

大部分时间一切正常。但有时，即使连接成功，当我尝试绑定到通知时，它也不起作用。

link是在这个函数里做的：

    _startNotifications(characteristicUuid) {
      let characteristic = this._characteristics.get(characteristicUuid);
      console.log(characteristic);
      return characteristic.startNotifications().then(() => characteristic);
    }

一切正常后，我可以在控制台中看到 BluetoothRemoteGATTCharacteristic 有一个 value : DataView(2) {} 否则，当它不工作时它有一个 value : null

如果我检测到该值为空，我希望能够自动重试。但我不熟悉 Promise（我认为就是它）并且 console.log(characteristic.value) 在这里不起作用。

你会如何处理这个问题？

Answer 1

我最终做的是 "bypass" 问题。所以这是一个比纯 Javascript 更算法的分辨率。

连接函数我没有改，所以还是这样调用:

device._startNotifications(some_uuid).then(handleHeartRateMeasurement)

我检查了 handleHeartRateMeasurement 函数中的所有内容：

var ready = false;

function handleHeartRateMeasurement(heartRateMeasurement) {
  console.log("Hold on...");
  heartRateMeasurement.addEventListener("characteristicvaluechanged", event => {
    // Everytime the value change, this should be triggered
    // If it did not, variable "ready" will stay false
    ready = true;
    var value = device.parseValue(event.target.value);
    // Do something with value here
  });

  var check = function(){
    // If we have received data from characteristic, we are ready to go !
    if(ready === false){
      console.log("Device connected but not receiving data");

      // Stop the current notification subscription
      device.stopNotificationsHeartRateMeasurement();

      // Start a new one
      device._startNotifications(some_uuid).then(handleHeartRateMeasurement);

      setTimeout(check, 1000); // check again in a 1s
    }
    else{
      console.log("Device connected and receiving data");
    }
  }

  setTimeout(() => {
    check();
  }, 500);
}

Web BLE 特性 startNotifications 有时不绑定

Web BLE Characteristic startNotifications sometimes doesn't bind

javascript

promise

web-bluetooth