Read Characteristic from rxBleDevice gives exception in Android, in iOS why it works fine using same UUID

Question

Currently i am working with an application where it involves reading data from the ble device. I am trying to read data from Andesfit Thermometer, Andesfit Blood Pressure, Andesfit Body Weight Scale.

For that i need to notify using Characteristic UUID. The notification stuff works fine and i am receiving data properly when any of the devices emits data.

Think about a situation where the user has already taken a measurement using the blood pressure machine. Then he picked up his device, got connected. I should be able to retrieve the last record and show it in the device.

In order to show the last record i need to read the characteristic using UUID

In iOS i am can retrieve the last record & notify using the same characteristic UUID and it is working fine.

 characteristic UUID is 2A1C

 peripheral.setNotifyValue(true, for: characteristic)
 peripheral.readValue(for: characteristic)

But in Android if i try to read using the characteristic UUID that used for notify it gives me exception.

rxBleDevice.establishConnection(false, Timeout(12000, TimeUnit.MILLISECONDS))
                .flatMapSingle { rxBleConnection ->

                    rxBleConnection.readCharacteristic(UUID.fromString("00002a1c-0000-1000-8000-00805f9b34fb"))
                        .subscribe({bytes ->

                    },{t: Throwable? ->
                        var mess = t!!.localizedMessage
                        t.printStackTrace()
                    })

Exception message is

GATT exception from MAC address F4:5E:AB:0D:7B:93, with type BleGattOperation{description='CHARACTERISTIC_READ'}

Here is my service discovery operation in Android

In my service discovery i can clearly see that this characteristic UUID is just meant for notify.

V/RxBle#ServiceDiscoveryOperation: Primary Service - Health Thermometer (00001809-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation: Instance ID: 51
V/RxBle#ServiceDiscoveryOperation: -> Characteristics:
V/RxBle#ServiceDiscoveryOperation:  * Temperature Measurement (00002a1c-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:    Properties: [ INDICATE ]
V/RxBle#ServiceDiscoveryOperation:    -> Descriptors: 
V/RxBle#ServiceDiscoveryOperation:      * Client Characteristic Configuration (00002902-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:      * Characteristic Presentation Format (00002904-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:  * Temperature Type (00002a1d-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:    Properties: [ READ ]
V/RxBle#ServiceDiscoveryOperation:  * Intermediate Temperature (00002a1e-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:    Properties: [ NOTIFY ]
V/RxBle#ServiceDiscoveryOperation:    -> Descriptors: 
V/RxBle#ServiceDiscoveryOperation:      * Client Characteristic Configuration (00002902-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:  * Measurement Interval (00002a21-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:    Properties: [ READ WRITE INDICATE ]
V/RxBle#ServiceDiscoveryOperation:    -> Descriptors: 
V/RxBle#ServiceDiscoveryOperation:      * Client Characteristic Configuration (00002902-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:      * Valid Range (00002906-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation: Primary Service - Battery Service (0000180f-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation: Instance ID: 65
V/RxBle#ServiceDiscoveryOperation: -> Characteristics:
V/RxBle#ServiceDiscoveryOperation:  * Battery Level (00002a19-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:    Properties: [ READ NOTIFY ]
V/RxBle#ServiceDiscoveryOperation:    -> Descriptors: 
V/RxBle#ServiceDiscoveryOperation:      * Client Characteristic Configuration (00002902-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation:      * Report Reference (00002908-0000-1000-8000-00805f9b34fb)
V/RxBle#ServiceDiscoveryOperation: --------------- ====== Finished peripheral content ====== ---------------

Dariusz Seweryn Dariusz Seweryn · Accepted Answer · 2019-10-25T14:42:47

why it works fine using same UUID (on iOS and on Android it does not)?

As you can see the characteristic you want to read has property [INDICATE] and not [READ]. Android OS checks permissions of the characteristic before performing an operation on it and does not allow to start one if the target characteristic does not have a corresponding property. iOS on the other hand executes the operation and the peripheral may (or may not) accept it regardless of this characteristic properties.

Read Characteristic from rxBleDevice gives exception in Android, in iOS why it works fine using same UUID

1 Answers