Android BLE - determine characteristic's stored value type

1
votes

My issue is with lack of ability to determine the type of the value, that read BLE characteristic has been storing. According to bluetooth spec. https://www.bluetooth.com/specifications/assigned-numbers/format-types those types are predefined by the standard and therefore GATT client should be able to read them.

My app is an attempt to create generic GATT client with ability to read any service and any characteristics it stores. For this I must have some universal way to read the type of characteristic, so that I am able to read it properly. For this I lack BLE API, that would allow this

I think simillar question is asked here: How to get BluetoothGattCharacteristic value format type? but question did get no answer.

Unfortunatelly current workaround would be to map UUID of specified in bluetooth characteristic, with the stored value's type. This solves lots of daily cases, but still is not enough to create completely generic GATT client.

1
androidbluetoothbluetooth-lowenergy

1 Answers

3
votes

Ok, I found the answer. For the people having simillar issue the answer lays not in BLE android API, but in bluetooth GATT specification.

It turns out, that some descriptors are mandatory and one of this is characteristic presentation format, specified here:

https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.characteristic_presentation_format.xml

there we can find the "hard coded value type", which is 8bit value and enum, which represents this value as the type. Based on this value we can deduce the characteristic's value type and read it properly.