need help to used window10 qt version 5.14.2 qbleutooth characteristicChanged Slot is not running，

qixin

hi guys,i copy this example to my project,write m_service->writeDescriptor(m_notificationDesc, QByteArray::fromHex("0100")); is ok,
devices can received.but device notify data is not can trigger characteristicChanged Slot, Hope that the big guys help to answer.Thank you

In some cases the peripheral generates value updates which the central is interested in receiving. In order for a characteristic to support such notifications it must have the QLowEnergyCharacteristic::Notify or QLowEnergyCharacteristic::Indicate property and a descriptor of type QBluetoothUuid::ClientCharacteristicConfiguration. Provided those conditions are fulfilled notifications can be enabled as shown in the following code segment:

  //PreCondition: service details already discovered
  QLowEnergyCharacteristic batteryLevel = service->characteristic(
              QBluetoothUuid::BatteryLevel);
  if (!batteryLevel.isValid())
      return;

  QLowEnergyDescriptor notification = batteryLevel.descriptor(
              QBluetoothUuid::ClientCharacteristicConfiguration);
  if (!notification.isValid())
      return;

  // establish hook into notifications
  connect(service, SIGNAL(characteristicChanged(QLowEnergyCharacteristic,QByteArray)),
          this, SLOT(characteristicChanged(QLowEnergyCharacteristic,QByteArray)));

  // enable notification
  service->writeDescriptor(notification, QByteArray::fromHex("0100"));

  // disable notification
  //service->writeDescriptor(notification, QByteArray::fromHex("0000"));

  // wait until descriptorWritten() signal is emitted
  // to confirm successful write

The example shows a battery level characteristic which updates the central on every value change. The notifications are provided via the characteristicChanged() signal. More details about this mechanism are provided by the Bluetooth Specification.

Paul Colby

Hi @qixin, your code looks right to me, assuming the device you're talking to does indeed support BLE Notify for that characteristic.

Two things I would try. First, update your connect to use the newer syntax, like:

    connect(service, &QLowEnergyService::characteristicChanged,
            this, &YourClassName::characteristicChanged);

This will just allow the compiler to catch any argument errors you might have there (though Qt should be logging an warning at runtime, if that was the problem).

(BTW, you can make that connection as soon as service is constructed if you like, so you don't miss the first characteristicChanged event ;)

Then, enable the QtBluetooth Logging Categories; something like this:

QLoggingCategory::setFilterRules(QStringLiteral("qt.bluetooth* = true"));

That might give you some hints to why its not working.

Cheers.

PS. Are you able / willing to tell us what device you're talking to? It might be helpful.

qixin

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qixin

This post is deleted!

qixin

hi it connected ble5.0 micro chip.thanks you very much! i used QLoggingCategory::setFilterRules(QStringLiteral("qt.bluetooth* = true")); can privide some information to find bug. now it can be used。
but i find new problem used void QLowEnergyController::connectionUpdated(const QLowEnergyConnectionParameters &newParameters) it can not running slot，seem not find information can solution. can you please some advice? thanks