CODEWITHSUNDEEP
androidbluetoothbluetooth-lowenergy
Chee-Yi
Chee-Yi

Reputation: 940

Cancelling BluetoothGatt read/write operation?

I'm new to BLE development on Android, and I'm looking at the API docs and don't see a way to cancel a read/write characteristic/descriptor operation that has been "queued" to the remote device. How can I achieve that?

Specifically, after calling the following, how to I cancel the write after a timeout (handled elsewhere using an AsyncTask)?

private void writeCharacteristic(BluetoothGatt gatt) {
    Log.i(TAG, "Writing to " + mCharacteristic);
    characteristic.setValue(mPayload);
    gatt.writeCharacteristic(mCharacteristic);
}

Upvotes: 0

Views: 975

Answers (2)

Emil
Emil

Reputation: 18452

You can't. A Write Request is sent over to the remote device and it answers with a Write Response. When the Write Response is received, the onCharacteristicWrite callback is called. There is no "cancellation" specified in the BLE protocol. Instead a 30 second timeout is specified. If the remote device does not send a Write Response within 30 seconds, the link is dropped. This is implemented for you in Android's Bluetooth stack. Since there may also only be one outstanding request at a time with the GATT protocol, there is no way to "retry" the operation.

Upvotes: 3

Roberto Betancourt
Roberto Betancourt

Reputation: 2505

I would advice against handling operations this way as it is not guaranteed that any Bluetooth LE operation will succeed or fail in X amount of time. Factors such as distance, interference etc will all affect your operation.

You will get a definite result of your operation on your BluetoothGattCallback methods. For example:

 @Override
        public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
            super.onCharacteristicWrite(gatt, characteristic, status);

      if (status==BluetoothGatt.SUCCESS)
          {
            //operation completed successfully
          }
           else
          {
           //operation failed
          }
}

All write/read operations for characteristics and descriptors deliver a result like that.

Upvotes: 0

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