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Geza Husi
2021-03-03 17:05:58 +01:00
committed by peter-pycom
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content/firmwareapi/pycom/network/bluetooth/gattccharacteristic.md
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@@ -42,12 +42,19 @@ characteristic.write(b'x0f')
#### characteristic.callback(trigger=None, handler=None, arg=None) #### characteristic.callback(trigger=None, handler=None, arg=None)
This method allows to register for notifications on the characteristic. Creates a callback that will be executed when any of the triggers occur. The arguments are:
* `trigger` can must be `Bluetooth.CHAR_NOTIFY_EVENT`. * `trigger` can be `Bluetooth.CHAR_NOTIFY_EVENT`.
* `handler` is the function that will be executed when the callback is triggered. * `handler` is the function that will be executed when the callback is triggered.
* `arg` is the argument that gets passed to the callback. If nothing is given, the characteristic object that owns the callback will be used. * `arg` is the argument that gets passed to the callback. If nothing is given, the characteristic object that owns the callback will be used.
Beyond the `arg` a tuple (called `data`) is also passed to `handler`. The tuple consists of (event, value), where `event` is the triggering event and `value` is the value strictly belonging to the `event`.
We recommend getting both the `event` and new `value` of the characteristic via this tuple, and not via `characteristic.event()` and `characteristic.value()` calls in the context of the `handler` to make sure no event and value is lost.
The reason behind this is that `characteristic.event()` and `characteristic.value()` return with the very last event received and with the current value of the characteristic, while the input parameters are always linked to the specific event triggering the `handler`. If the device is busy executing other operations, the `handler` of an incoming event may not be called before the next event occurs and is processed.
Usage example can be found under GATTSCharacteristic page.
#### characteristic.read\_descriptor(uuid) #### characteristic.read\_descriptor(uuid)
Returns the value of the descriptor specified by the `uuid` parameter. If no descriptor found for the characteristic returns None. Returns the value of the descriptor specified by the `uuid` parameter. If no descriptor found for the characteristic returns None.