Bluetooth LE with Android Studio: Write Characteristic with buttons - android-studio

Question

I am new to Android and Bluetooth and suffering with this problem.
I want to write on a specific characteristic if two buttons are touched.
If I touch the first button a number between 0-9 should be count with +1. With the other button the number should be decrease with -1.
As a fundament i use the BluetootleGatt Example App from Google.
In the DeviceControlActivity i changed the following code:
private final ExpandableListView.OnChildClickListener servicesListClickListner =
new ExpandableListView.OnChildClickListener() {
#Override
public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
int childPosition, long id) {
if (mGattCharacteristics != null) {
final BluetoothGattCharacteristic characteristic =
mGattCharacteristics.get(groupPosition).get(childPosition);
final int charaProp = characteristic.getProperties(); //The properties contain a bit mask of property flags indicating
//the features of this characteristic.
if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
// 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) {
mNotifyCharacteristic = characteristic;
mBluetoothLeService.setCharacteristicNotification(
characteristic, true);
}
if ((charaProp | BluetoothGattCharacteristic.PROPERTY_WRITE) > 0) {
characteristic.setWriteType(BluetoothGattCharacteristic.PERMISSION_WRITE);
addListenerOnButton();
}
return true;
}
return false;
}
};
Here is my addListenerOnButton() for the two buttons:
public void addListenerOnButton() {
mArrowUp = (ImageButton) findViewById(R.id.arrow_up);
mArrowUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
mBluetoothLeService.writeCharacteristicUp();
}
});
mArrowDown = (ImageButton) findViewById(R.id.arrow_down);
mArrowDown.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
mBluetoothLeService.writeCharacteristicDown();
}
});
}
They will call the two writeCharacteristic Methods in the BluetoothLeService-Class. For example i post here only the writeCharacteristicUp()-Method:
public boolean writeCharacteristicUp() {
//check mBluetoothGatt is available
if (mBluetoothGatt == null) {
Log.e(TAG, "lost connection");
return false;
}
BluetoothGattService Service = mBluetoothGatt.getService(UUID_DO_LOGGER_TEST);
if (Service == null) {
Log.e(TAG, "service not found!");
return false;
}
BluetoothGattCharacteristic charac = Service
.getCharacteristic(UUID_TEST_NUMBER);
if (charac == null) {
Log.e(TAG, "char not found!");
return false;
}
byte[] value0 = new byte[1];
value0[0] = (byte) 0; //Constant of 0 for comparison later
byte[] value1 = new byte[1];
value1[0] = (byte) 1; //Constant of 1 for comparison later
byte[] value2 = new byte[1];
value2[0] = (byte) 2; //Constant of 1 for comparison later
byte[] value3 = new byte[1];
value3[0] = (byte) 3; //Constant of 1 for comparison later
byte[] value4 = new byte[1];
value4[0] = (byte) 4; //Constant of 1 for comparison later
byte[] value5 = new byte[1];
value5[0] = (byte) 5; //Constant of 1 for comparison later
byte[] value6 = new byte[1];
value6[0] = (byte) 6; //Constant of 1 for comparison later
byte[] value7 = new byte[1];
value7[0] = (byte) 7; //Constant of 1 for comparison later
byte[] value8 = new byte[1];
value8[0] = (byte) 8; //Constant of 1 for comparison later
byte[] value9 = new byte[1];
value9[0] = (byte) 9; //Constant of 1 for comparison later
byte[] actualvalue = charac.getValue();
if (actualvalue == value0) {
charac.setValue(value1);
}
if (actualvalue == value1) {
charac.setValue(value2);
}
if (actualvalue == value2) {
charac.setValue(value3);
}
if (actualvalue == value3) {
charac.setValue(value4);
}
if (actualvalue == value4) {
charac.setValue(value5);
}
if (actualvalue == value5) {
charac.setValue(value6);
}
if (actualvalue == value6) {
charac.setValue(value7);
}
if (actualvalue == value7) {
charac.setValue(value8);
}
if (actualvalue == value8) {
charac.setValue(value9);
}
if (actualvalue == value9) {
charac.setValue(value0);
}
// charac.setValue(value0);
// byte[] actualvaluenew1 = charac.getValue();
boolean status = mBluetoothGatt.writeCharacteristic(charac);
// byte[] actualvaluenew2 = charac.getValue();
return status;
}
The problem is that the
boolean status = mBluetoothGatt.writeCharacteristic(charac)
does not work, the status will be false. And so the actual value is not displayed on the Screen in the corresponding TextView. Why?
Also i found out that the if-grinds are not working because charac.setValue(value0) is only working outside the if-grinds?

Answer 1

I would suggest you press and hold control key and click to BluetoothGatt#writeCharacteristic(ch) function in your code. Then Android Studio will view BluetoothGatt#writeCharacteristic(BluetoothGattCharacteristic characteristic) function:
public boolean writeCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_WRITE) == 0
&& (characteristic.getProperties() &
BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE) == 0) return false;
if (VDBG) Log.d(TAG, "writeCharacteristic() - uuid: " + characteristic.getUuid());
if (mService == null || mClientIf == 0 || characteristic.getValue() == null) return false;
BluetoothGattService service = characteristic.getService();
if (service == null) return false;
BluetoothDevice device = service.getDevice();
if (device == null) return false;
synchronized(mDeviceBusy) {
if (mDeviceBusy) return false;
mDeviceBusy = true;
}
try {
mService.writeCharacteristic(mClientIf, device.getAddress(),
service.getType(), service.getInstanceId(),
new ParcelUuid(service.getUuid()), characteristic.getInstanceId(),
new ParcelUuid(characteristic.getUuid()),
characteristic.getWriteType(), AUTHENTICATION_NONE,
characteristic.getValue());
} catch (RemoteException e) {
Log.e(TAG,"",e);
mDeviceBusy = false;
return false;
}
return true;
}
Put a breakpoint inside the method and do debugging. Here are the possible reasons why you get false based on the source code:
The remote BLE device does not have Write or Write with No Response access
Either your service is null or the characteristic value you set is null
Your device is already doing another BLE process with the remote device
In my opinion, most probably the 2nd item is the reason.