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In attempting to read the value of a Bluetooth Low-Energy GATT characteristic in the Android API 18, I came across the following dilemma: What is the proper way to retrieve the value stored in a characteristic? And at which level of the stack should this action take place?

In conducting my own research, I stumbled upon what I understand are two possible methods:

  • BluetoothGatt.readCharacteristic(BluetoothGattCharacteristic characteristic)

  • BluetoothGattCharacteristic.getValue()

    public void onClick(View v){        
    byteValue = mBTValueCharacteristic.getValue();
    if ((byteValue[0] & 0x01) == 1)
        byteValue[0] = 0x00;
    else
        byteValue[0] = 0x01;

    mBTValueCharacteristic.setValue(byteValue);
    mBTGatt.writeCharacteristic(mBTValueCharacteristic);
}

Above is the original code which led me to this issue. In it, I attempt to read the value of a characteristic, and simply toggle its state using a button.

estebro
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1 Answers1

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BluetoothGatt.readCharacteristic(BluetoothGattCharacteristic characteristic)

This function is updating your BluetoothGattCharacteristic object (on your Android device) using characteristic value from the Bluetooth .

BluetoothGattCharacteristic.getValue()

This function is just a getter function of the BluetoothGattCharacteristic object. There is not any transaction between android and the bluetooth device.

reTs
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  • Thank you for the clarification, but I have one more question then. Do you think I can both read the characteristic and obtain its value within the same click action? Will there be a timing issue due to the nature of the wireless connection? – estebro Nov 16 '13 at 22:36
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    Wait until onCharacteristicRead callback fires, or else you are just getting the old value. – reTs Nov 17 '13 at 08:13