Android 4.3 BLE how to write Characteristic

Question

Followed sample

I know:

• How to read Characteristic value.

But I don't know:

• How to write data to the firmware.

I tried several times, but it did not work.

This is the coding:

if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
                System.out.println("read!!!!!!");
                // If there is an active notification on a characteristic,
                // clear
                // it first so it doesn't update the data field on the user
                // interface.
                if (mNotifyCharacteristic != null) {
                    mBluetoothLeService.setCharacteristicNotification(
                            mNotifyCharacteristic, false);
                    mNotifyCharacteristic = null;
                }
                mBluetoothLeService.readCharacteristic(characteristic);
            }
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {
                System.out.println("notify!!!!!!");
                mNotifyCharacteristic = characteristic;
                mBluetoothLeService.setCharacteristicNotification(
                        characteristic, true);
            }
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_WRITE) > 0) {
                if (SampleGattAttributes.AppConfigToBongCharacteristicUUID
                        .equals(characteristic.getUuid())) {
                    System.out.println("write!!!!!!");
                    mBluetoothLeService.writeCharacteristic(characteristic);
                }
            }



public void writeCharacteristic(BluetoothGattCharacteristic characteristic) {
    if (mBluetoothAdapter == null || mBluetoothGatt == null) {
        Log.w(TAG, "BluetoothAdapter not initialized");
        return;
    }
    if (UUID_SEND_CONFIG_TO_BONG.equals(characteristic.getUuid())) {

        Calendar date = Calendar.getInstance();
        StringBuilder data = new StringBuilder();
        String data_date_y = String.format("%4s", date.get(Calendar.YEAR))
                .replace(' ', '0');
        String data_date_m = String.format("%2s", date.get(Calendar.MONTH))
                .replace(' ', '0');
        String data_date_d = String.format("%2s", date.get(Calendar.DATE))
                .replace(' ', '0');
        String data_date_h = String.format("%2s", date.get(Calendar.HOUR))
                .replace(' ', '0');
        String data_date_min = String.format("%2s",
                date.get(Calendar.MINUTE)).replace(' ', '0');

        data.append("10FFFF");
        data.append(data_date_y);
        data.append(data_date_m);
        data.append(data_date_d);
        data.append(data_date_h);
        data.append(data_date_min);
        System.out.println(data);
        byte[] dataByte = data.toString().getBytes();

        characteristic.setValue(dataByte);
        mBluetoothGatt.writeCharacteristic(characteristic);
    }

}

//onCharacteristicWrite() Not being called

@Override
    public void onCharacteristicWrite(BluetoothGatt gatt,
            BluetoothGattCharacteristic characteristic, int status) {
        System.out.println("writeCharacteristic111");
        System.out.println("status:" + status);
        System.out.println(BluetoothGatt.GATT_SUCCESS);
        if (status == BluetoothGatt.GATT_SUCCESS) {
            broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
        }
    }

Answer 1

I think jkraybill has got the answer for you.

I was using google's bluetooth le sample code, which checks properties bit with '|' operation as following:

if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
    ...
}

But when I looked into BluetoothGatt code itself, I found it's using '&' operation instead.

public boolean writeCharacteristic(BluetoothGattCharacteristic characteristic) {
    if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_WRITE) == 0
        && (characteristic.getProperties() &
            BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE) == 0) return false;

    ...
}

So obviously the sample code was incorrect, if you check further on its definition on Google develop doc: https://developer.android.com/reference/android/bluetooth/BluetoothGattCharacteristic.html

Answer 2

You must specify the value that you would like to write. you can find what you need in this example