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I'm developing a project that consists of a BLE GATT server ran on Android phone (using BluetoothGattServer Java class) and a BLE client on an IoT board. The concept of using the phone as the server is to somehow protect the IoT board from attacking clients. When my Android application wants to talk to the external device it starts advertising a special set of data and if the external device recognizes the advertisment it connects to the Android BLE GATT server. Then the external device reads the presented services and chareacteristics and registers for notifications on some of the chars.
By far it all happens well.
After that the external device tries to write authentication data to one of the chars. If everything was clean and perfect, the process goes well. But if for a reason the last connection broke in the middle of some operation and was not properly closed, the external device cannot read/write the characteristic. If I restart the phone or clear Bluetooth cache (Settings > Apps > Bluetooth > Clear Data) all the operations proceed fine, but I cannot force users to do this in normal operation and I haven't found how and if I could clear this cache programmatically from inside the app.
I read over the web for GATT client cache undocumented "Refresh" method, but in GATT server there is no such.
I read about and tried the "Service changed" characteristic (0x2A05) but it doesn't help me much.
Having doubts about which of the devices is causing the problem I have tried with another phone as a client. I ran "BLE Scanner" App on it and tried to connect to the server phone - the problem persists. I can connect, all the characteristics are discovered, but when I try to read/write some char the connection brakes after a 30 sec timeout - exactly the same behavior like in the original situation. The conclusion is I have a problem with Android BluetoothGattServer.
During the development the problem occurs mostly when connection is broken by some error in communication. In real life usage after I have all errors fixed that will not happen, but having in mind tha it is wireless radio connection, it can be disconnected by literally everything and I shall have a reliable mechanism to reconnect.
I open the server with this code:
private void startServer() {
BluetoothAdapter bluetoothAdapter = mBluetoothManager.getAdapter();
mBluetoothLeAdvertiser = bluetoothAdapter.getBluetoothLeAdvertiser();
if (mBluetoothLeAdvertiser == null) {
Log.w("BLE", "Failed to create advertiser");
return;
}
AdvertiseSettings settings = new AdvertiseSettings.Builder()
.setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY)
.setConnectable(true)
.setTimeout(0)
.setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_HIGH)
.build();
byte bData[] = new byte[24];
bData = ...... // some proprietary advertising data
AdvertiseData data = new AdvertiseData.Builder()
.setIncludeDeviceName(false)
.setIncludeTxPowerLevel(false)
.addManufacturerData(iManufID, bData)
.build();
mBluetoothLeAdvertiser
.startAdvertising(settings, data, mAdvertiseCallback);
mBluetoothGattServer = mBluetoothManager.openGattServer(ctxActivity, mGattServerCallback);
mBluetoothGattServer.clearServices();
mBluetoothGattServer.addService(BLEProfile.createBLEService());
/* Static method, which builds Service->Chars->Descriptors.
I assign the Client Config descriptor (0x2902) to each characteristic. */
}
For stopping the sertver I use this code:
private void stopServer() {
if (mBluetoothGattServer == null) return;
mBluetoothGattServer.clearServices();
mBluetoothGattServer.close();
if (mBluetoothLeAdvertiser == null) return;
mBluetoothLeAdvertiser.stopAdvertising(mAdvertiseCallback);
}
I stop and start the server each time a connection was broken.
Does anyone have an idea what am I doing wrong?
Also it is important to mention that in real life IoT devices will be many in a room, phones may be many in a room. One phone should be able to be connected by any of the IoT devices it requests sequentially and one IoT device should be able to connect to more than one phone sequentially. The advertising data of the phone's GATT Server defines which of the IoT devices is requested to connect and it will change each time the phone requests connection with a different device.
Update:
Here is the code for the Server Callback:
private BluetoothGattServerCallback mGattServerCallback = new BluetoothGattServerCallback() {
#Override
public void onMtuChanged(BluetoothDevice device, int mtu) {
super.onMtuChanged(device, mtu);
Log.i("BLE", "MTU changed: "+mtu);
}
#Override
public void onCharacteristicWriteRequest(BluetoothDevice device, int requestId, BluetoothGattCharacteristic characteristic, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) {
if(BLEProfile.XXXXXX.equals(characteristic.getUuid()))
{
// ... some data checks ...
mBluetoothGattServer.sendResponse(device,
requestId,
iValid,
0,
bEncrypted);
characteristic.setValue(bEncrypted);
mBluetoothGattServer.notifyCharacteristicChanged(device, characteristic, true);
} else if (...) /* similar operations for all other characteristics */
{
...
}
else
{
Log.i("BLE", "Write not mine characteristic");
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_FAILURE,
0,
null);
}
}
#Override
public void onConnectionStateChange(BluetoothDevice device, int status, int newState) {
if (newState == BluetoothProfile.STATE_CONNECTED) {
Log.i("BLE", "BluetoothDevice ... CONNECTED: " + device);
if(device != null)
{
BluetoothGattService mServ = mBluetoothGattServer.getService(BLEProfile.GATT_SERVICE);
if(mServ != null)
{
BluetoothGattCharacteristic mChar = mServ.getCharacteristic(BLEProfile.SERVICE_CHANGED);
if(mChar != null)
mBluetoothGattServer.notifyCharacteristicChanged(device, mChar, false);
}
}
} else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
mRegisteredDevices.remove(device);
stopAdvertising();
startAdvertising();
}
}
#Override
public void onCharacteristicReadRequest(BluetoothDevice device, int requestId, int offset,
BluetoothGattCharacteristic characteristic) {
/* Not used currently. Just some testing code below. */
if(BLEProfile.XXXXXX.equals(characteristic.getUuid()))
{
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_SUCCESS,
0,
new byte[] {0x01, 0x02, 0x03, 0x04, 0x05});
} else if(...) /* similar operations for all other characteristics */
{
...
}
else
{
Log.i("BLE", "Read not mine characteristic");
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_FAILURE,
0,
null);
}
}
#Override
public void onDescriptorReadRequest(BluetoothDevice device, int requestId, int offset,
BluetoothGattDescriptor descriptor) {
if (BLEProfile.CLIENT_CONFIG.equals(descriptor.getUuid())) {
Log.d("BLE", "Config descriptor read");
byte[] returnValue;
if (mRegisteredDevices.contains(device)) {
returnValue = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE;
} else {
returnValue = BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE;
}
/* Not sure why I am responding with GATT_FAILURE here insted of GAT_SUCCESS !?!? May be some copy/paste mistake. */
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_FAILURE,
0,
returnValue);
} else {
Log.w("BLE", "Unknown descriptor read request");
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_FAILURE,
0,
null);
}
}
#Override
public void onDescriptorWriteRequest(BluetoothDevice device, int requestId,
BluetoothGattDescriptor descriptor,
boolean preparedWrite, boolean responseNeeded,
int offset, byte[] value) {
if (BLEProfile.CLIENT_CONFIG.equals(descriptor.getUuid())) {
if (Arrays.equals(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE, value)) {
Log.i("BLE", "Subscribe device to notifications: " + device);
mRegisteredDevices.add(device);
} else if (Arrays.equals(BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE, value)) {
Log.i("BLE", "Unsubscribe device from notifications: " + device);
mRegisteredDevices.remove(device);
}
if (responseNeeded) {
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_SUCCESS,
0,
null);
}
} else {
Log.w("BLE", "Unknown descriptor write request");
if (responseNeeded) {
mBluetoothGattServer.sendResponse(device,
requestId,
BluetoothGatt.GATT_FAILURE,
0,
null);
}
}
}
};
I have just connected to ble device successfully, and enabled the notifications for read and write. but after i set value true and call writecharacteristics method i can write to device and get write empty response from bledevice..
What should be the flow of a write request to ble device?
public void onServicesDiscovered(BluetoothGatt bluetoothGatt, int i) {
BLEService.this.f8468j = BLEService.this.f8466h.getCharacteristic(BLEService.this.f8462d);//readchar.
BLEService.this.f8467i = BLEService.this.f8466h.getCharacteristic(BLEService.this.f8460b);//writechar.
setcharacteristicnotification(true, bluetoothgat, BLEService.this.f8467i);
// i need to writechar right now in here. but ondeviceresult returns "write_empty"... what is wrong?
bArr = new byte[]{97,48,24,69,96,27,79,91,55,7,30,63,87,84,7,87}
this.BluetoothGattCharacteristicwrite.setValue(bArr);
this.BluetoothGatt.writeCharacteristic(this.BluetoothGattCharacteristicwrite);
super.onServicesDiscovered(bluetoothGatt, i);
}
};
-
private void setcharacteristicnotification(boolean z, BluetoothGatt bluetoothGatt, BluetoothGattCharacteristic bluetoothGattCharacteristic) {
if (bluetoothGatt != null && bluetoothGattCharacteristic != null) {
bluetoothGatt.setCharacteristicNotification(bluetoothGattCharacteristic, z);
BluetoothGattDescriptor descriptor = bluetoothGattCharacteristic.getDescriptor(BLEService.this.f8463e);
if (descriptor != null) {
descriptor.setValue(z ? BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE : BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE);
BLEService.this.f8465g.writeDescriptor(descriptor);
}
//("BLEService", "=== enableNotification isWriting = true ===");
BLEService.this.m11448a(7);
}
}
You can't have multiple outstanding GATT requests at a time. Now you call writeDescriptor followed by writeCharacteristic without waiting for onDescriptorWrite.
Im trying to read the value stored in a BluetoothGattCharacteristic. The following is my BluetoothGattCallback code, where most of the action takes place:
private final BluetoothGattCallback mGattCallback =
new BluetoothGattCallback() {
#Override
public void onConnectionStateChange(BluetoothGatt gatt, int status,
int newState) {
if (newState == BluetoothProfile.STATE_CONNECTED) {
Log.i(TAG, "Connected to GATT server.");
Log.i(TAG, "Getting services....");
gatt.discoverServices();
} else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
Log.i(TAG, "Disconnected from GATT server.");
}
}
#Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
BluetoothGattService serv = gatt.getService(Constants.MY_UUID);
if (serv != null) {
BluetoothGattCharacteristic characteristic = serv.getCharacteristic(Constants.ANOTHER_UUID);
boolean res = gatt.readCharacteristic(characteristic);
if (res) {
Log.d(TAG, "res was true");
} else {
Log.d(TAG, "res was false");
}
}
} else {
Log.w(TAG, "onServicesDiscovered received: " + status);
}
}
#Override
public void onCharacteristicRead(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
Log.d(TAG, "Succesfully read characteristic: " + characteristic.getValue().toString());
} else {
Log.d(TAG, "Characteristic read not successful");
}
}
};
So to read from the characteristic, i'm attempting to use the gatt.readCharacteristic() method, which takes a characteristic and returns a boolean indicating a successful operation or not. Here, this method is returning false (printing "res was false"), indicating it failed.
There is no error message being printed. What is the proper way to read a characteristic? Why would this method be returning false?
EDIT:
As suggested by Inferno, went ahead and downloaded the needed sources and then set a breakpoint in the BluetoothGatt readCharacteristic() method:
Here is the readCharacteristic() method in android-23..\BluetoothGatt
public boolean readCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() &
BluetoothGattCharacteristic.PROPERTY_READ) == 0) return false;
(characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_READ) is returning 0 so false is being immediately returned. Now according to the debugger characteristic.getProperties() is returning a value of 8, while BluetoothGattCharacteristic.PROPERTY_READ has a static int value of 0x02.
As I understand, 0x08 & 0x02 == 0. Since the PROPERTY_READ is a hardcoded value, I assume something is wrong with the value returned from characteristic.getProperties(). What could be going wrong here?
What is the proper way to read a characteristic?
First of all, you call gatt.readCharacteristic(characteristic) from inside of the onServicesDiscovered() callback, which is alright. I can't see any serious flaws in your code.
What you could add in onConnectionStateChange() is an additional check before you verify newState == BluetoothProfile.STATE_CONNECTED:
if (status == BluetoothGatt.GATT_SUCCESS) { ...
Why would this method be returning false?
I checked the android source of BluetoothGatt here and it turns out, the return value of false is returned in many different cases as you can see in the code below:
public boolean readCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() &
BluetoothGattCharacteristic.PROPERTY_READ) == 0) return false;
if (VDBG) Log.d(TAG, "readCharacteristic() - uuid: " + characteristic.getUuid());
if (mService == null || mClientIf == 0) 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.readCharacteristic(mClientIf, device.getAddress(),
characteristic.getInstanceId(), AUTHENTICATION_NONE);
} catch (RemoteException e) {
Log.e(TAG,"",e);
mDeviceBusy = false;
return false;
}
return true;
}
So what I recommend you to do is, start the debugger in Android Studio and set a breakpoint inside the readCharacteristic() method (in BluetoothGatt.java) and carefully step through the code to see where false gets returned. That way you will hopefully be able to localize the issue. Besides that, anything else would be wild guessing.
Of course you need to have the sources downloaded to be able to view BluetoothGatt.java. But Android Studio will give you a small yellow bar at the top of the editor which asks you if you want to download and install. Just do it and restart Android Studio after the download is complete. Then you should be able to set a breakpoint in BluetoothGatt.java.
UPDATE:
As I understand, 0x08 & 0x02 == 0. Since the PROPERTY_READ is a
hardcoded value, I assume something is wrong with the value returned
from characteristic.getProperties(). What could be going wrong here?
According to BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part G] page 533, the value of 0x8 which is returned by characteristic.getProperties() means, that your characteristic has write only permissions. Not a surprise that all reading attempts fail. In other words: your bluetooth device does not allow you to read that particular characteristic.
Quote from the specification:
The Characteristic Properties bit field determines how the Characteristic Value
can be used, or how the characteristic descriptors (see Section 3.3.3) can be
accessed.
I was trying to read data back from a cow brush scratcher that had BLE chip.
It was under a read characteristic on a BLE module.
The data was coming back in hex i.e. 0x00 for BRUSH_OFF & 0x01 for BRUSH_ON
I was trying to read in this data in my android app and it kept coming back as blank.
Problem is 0x00 = NUll in ascii and 0x01 = SOH ascii it cannot be displayed on the screen.
0x30 = 0 in ascii 0x31 = 1 in ascii
Maybe you have escape characters coming back in hex and they cannot be read.
I spent months trying to figure out why i couldn't read back the values.
Hope this might help you.
I'm trying to write an Android app that mimics functionality already present in an iOS app I wrote. I am interfacing with 2 different BLE devices:
Blood Pressure Cuff
Weight Scale
On iOS, I have both devices working well and reporting data. On Android, I can't get it to work. After hours of research and testing, I think the basic issue I'm trying to solve is this:
On iOS, I call the following code to enable the BLE device to notify my iOS device when it has data to report:
#pragma mark - CBPeripheralDelegate Protocol methods
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error {
for (CBCharacteristic *characteristic in [service characteristics]) {
[peripheral setNotifyValue:YES forCharacteristic:characteristic];
}
}
That's it. The notes for this method in iOS say the following:
If the specified characteristic is configured to allow both notifications and indications, calling this method enables notifications only.
Based on that (and the fact that it works in iOS), I'm figuring that the configuration descriptor for the characteristic for which I want notifications should be configured like this:
descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
gatt.writeDescriptor(descriptor);
With that in mind, my BLEDevice class looks like this:
public abstract class BLEDevice {
protected BluetoothAdapter.LeScanCallback mLeScanCallback;
protected BluetoothGattCallback mBluetoothGattCallback;
protected byte[] mBytes;
protected Context mContext;
protected GotReadingCallback mGotReadingCallback;
protected String mDeviceName;
public final static UUID UUID_WEIGHT_SCALE_SERVICE
= UUID.fromString(GattAttributes.WEIGHT_SCALE_SERVICE);
public final static UUID UUID_WEIGHT_SCALE_READING_CHARACTERISTIC
= UUID.fromString(GattAttributes.WEIGHT_SCALE_READING_CHARACTERISTIC);
public final static UUID UUID_WEIGHT_SCALE_CONFIGURATION_CHARACTERISTIC
= UUID.fromString(GattAttributes.WEIGHT_SCALE_CONFIGURATION_CHARACTERISTIC);
public final static UUID UUID_WEIGHT_SCALE_CONFIGURATION_DESCRIPTOR
= UUID.fromString(GattAttributes.WEIGHT_SCALE_CONFIGURATION_DESCRIPTOR);
abstract void processReading();
interface GotReadingCallback {
void gotReading(Object reading);
}
public BLEDevice(Context context, String deviceName, GotReadingCallback gotReadingCallback) {
mContext = context;
BluetoothManager btManager = (BluetoothManager)mContext.getSystemService(Context.BLUETOOTH_SERVICE);
final BluetoothAdapter btAdapter = btManager.getAdapter();
if (btAdapter != null && !btAdapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
mContext.startActivity(enableIntent);
}
mDeviceName = deviceName;
mBluetoothGattCallback = new BluetoothGattCallback() {
#Override
public void onCharacteristicChanged(BluetoothGatt gatt, final BluetoothGattCharacteristic characteristic) {
byte[] data = characteristic.getValue();
mBytes = data;
Log.d("BluetoothGattCallback.onCharacteristicChanged", "data: " + data.toString());
}
#Override
public void onConnectionStateChange(final BluetoothGatt gatt, final int status, final int newState) {
// this will get called when a device connects or disconnects
if (newState == BluetoothProfile.STATE_CONNECTED) {
gatt.discoverServices();
} else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
if (mBytes != null) {
processReading();
}
}
}
#Override
public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
super.onDescriptorWrite(gatt, descriptor, status);
Log.d("onDescriptorWrite", "descriptor: " + descriptor.getUuid() + ". characteristic: " + descriptor.getCharacteristic().getUuid() + ". status: " + status);
}
#Override
public void onServicesDiscovered(final BluetoothGatt gatt, final int status) {
// this will get called after the client initiates a BluetoothGatt.discoverServices() call
BluetoothGattService service = gatt.getService(UUID_WEIGHT_SCALE_SERVICE);
if (service != null) {
BluetoothGattCharacteristic characteristic;
characteristic = service.getCharacteristic(UUID_WEIGHT_SCALE_READING_CHARACTERISTIC);
if (characteristic != null) {
gatt.setCharacteristicNotification(characteristic, true);
}
characteristic = service.getCharacteristic(UUID_WEIGHT_SCALE_CONFIGURATION_CHARACTERISTIC);
if (characteristic != null) {
BluetoothGattDescriptor descriptor = characteristic.getDescriptor(UUID_WEIGHT_SCALE_CONFIGURATION_DESCRIPTOR);
if (descriptor != null) {
descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
gatt.writeDescriptor(descriptor);
}
}
}
}
};
mLeScanCallback = new BluetoothAdapter.LeScanCallback() {
#Override
public void onLeScan(final BluetoothDevice device, final int rssi, final byte[] scanRecord) {
Log.d("LeScanCallback", device.toString());
if (device.getName().contains("{Device Name}")) {
BluetoothGatt bluetoothGatt = device.connectGatt(mContext, false, mBluetoothGattCallback);
btAdapter.stopLeScan(mLeScanCallback);
}
}
};
btAdapter.startLeScan(mLeScanCallback);
}
}
NOTE: It might be important to know that these 2 devices function in the following way:
The BLE device is turned on an a measurement is initiated on the device.
Once the measurement has been taken, the BLE device attempts to initiate a BLE connection.
Once the BLE connection is made, the device pretty much immediately sends the data, sometimes sending a couple of data packets. (If previous data measurements haven't been successfully sent over BLE, it keeps them in memory and sends all of them, so I only really care about the final data packet.)
Once the final data packet is sent, the BLE device disconnects rapidly.
If the BLE device fails to send data (as is currently happening on the Android app), the BLE device disconnects pretty rapidly.
In my LogCat, I see a lot of output that's exactly like I'd expect.
I see a list of services like I expect, including the data service I want.
I see a list of characteristics like I expect, including the data characteristic I want.
I see a list of descriptors like I expect, including the "configuration" (0x2902) descriptor.
The most recent failure I'm experiencing is a status of "128" being reported in onCharacteristicWrite. The comments to question #3 (below) seem to indicate this is a resource issue.
I've looked at the following questions:
Android BLE onCharacteristicChanged not called
Android BLE, read and write characteristics
Android 4.3 onDescriptorWrite returns status 128
Here's why they don't give me what I need:
This question's answer was not to read the descriptor's value. I'm not doing that, so that can't be what's getting in the way.
This is basically an overview of the various methods that are available, which I think I now understand. The big key in this question/answer is not to write multiple times to different descriptors, but I'm also not doing that. I only care about the one characteristic.
This question/answer seems to be related to BLE resource limitations, but I don't think this applies. I'm only connecting this one device and I'm trying to do a very, very simple data transfer. I don't think I'm hitting resource ceilings.
I've tried a bunch of examples and tutorials, including Google's Android sample code. None of them seem to enable the BLE device to notify my Android device of data updates. It's obviously not the device, since the iOS version works. So, what is the iOS code doing in the background to get the notifications to work and what code on the Android side will mimic that functionality?
EDIT/UPDATE
Based on #yonran's comments, I updated my code by changing the onServicesDiscovered implementation to this:
#Override
public void onServicesDiscovered(final BluetoothGatt gatt, final int status) {
// this will get called after the client initiates a BluetoothGatt.discoverServices() call
BluetoothGattService service = gatt.getService(UUID_WEIGHT_SCALE_SERVICE);
if (service != null) {
BluetoothGattCharacteristic characteristic = service.getCharacteristic(UUID_WEIGHT_SCALE_READING_CHARACTERISTIC);
if (characteristic != null) {
if (gatt.setCharacteristicNotification(characteristic, true) == true) {
Log.d("gatt.setCharacteristicNotification", "SUCCESS!");
} else {
Log.d("gatt.setCharacteristicNotification", "FAILURE!");
}
BluetoothGattDescriptor descriptor = characteristic.getDescriptors().get(0);
if (0 != (characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE)) {
// It's an indicate characteristic
Log.d("onServicesDiscovered", "Characteristic (" + characteristic.getUuid() + ") is INDICATE");
if (descriptor != null) {
descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
gatt.writeDescriptor(descriptor);
}
} else {
// It's a notify characteristic
Log.d("onServicesDiscovered", "Characteristic (" + characteristic.getUuid() + ") is NOTIFY");
if (descriptor != null) {
descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
gatt.writeDescriptor(descriptor);
}
}
}
}
}
That does seem to have changed some things a little bit. Here's the current Logcat, following that code change:
D/BluetoothGatt﹕ setCharacteristicNotification() - uuid: <UUID> enable: true
D/gatt.setCharacteristicNotification﹕ SUCCESS!
D/onServicesDiscovered﹕ Characteristic (<UUID>) is INDICATE
D/BluetoothGatt﹕ writeDescriptor() - uuid: 00002902-0000-1000-8000-00805f9b34fb
D/BluetoothGatt﹕ onDescriptorWrite() - Device=D0:5F:B8:01:6C:9E UUID=<UUID>
D/onDescriptorWrite﹕ descriptor: 00002902-0000-1000-8000-00805f9b34fb. characteristic: <UUID>. status: 0
D/BluetoothGatt﹕ onClientConnectionState() - status=0 clientIf=6 device=D0:5F:B8:01:6C:9E
So, it would appear that I'm now setting everything up properly (since setCharacteristicNotification returns true and the onDescriptorWrite status is 0). However, onCharacteristicChanged still never fires.
I've been able to successfully catch onCharacteristicChanged() with multiple services and characteristics by:
Writing descriptor values in the broadcastReceiver() in the main loop after service discovery is finished.
private final BroadcastReceiver UARTStatusChangeReceiver = new BroadcastReceiver() {
//more code...
if (action.equals(uartservice.ACTION_GATT_SERVICES_DISCOVERED)) {
mService.enableTXNotification();
}
and
By adding a delay between descriptor value settings
public void enableTXNotification(){
/*
if (mBluetoothGatt == null) {
showMessage("mBluetoothGatt null" + mBluetoothGatt);
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_UART);
return;
}
*/
/**
* Enable Notifications for the IO service and characteristic
*
*/
BluetoothGattService IOService = mBluetoothGatt.getService(IO_SERVICE_UUID);
if (IOService == null) {
showMessage("IO service not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_IO);
return;
}
BluetoothGattCharacteristic IOChar = IOService.getCharacteristic(IO_CHAR_UUID);
if (IOChar == null) {
showMessage("IO charateristic not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_IO);
return;
}
mBluetoothGatt.setCharacteristicNotification(IOChar,true);
BluetoothGattDescriptor descriptorIO = IOChar.getDescriptor(CCCD);
descriptorIO.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
mBluetoothGatt.writeDescriptor(descriptorIO);
/**
* For some reason android (or the device) can't handle
* writing one descriptor after another properly. Without
* the delay only the first characteristic can be caught in
* onCharacteristicChanged() method.
*/
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
/**
* Enable Indications for the RXTX service and characteristic
*/
BluetoothGattService RxService = mBluetoothGatt.getService(RXTX_SERVICE_UUID);
if (RxService == null) {
showMessage("Rx service not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_UART);
return;
}
BluetoothGattCharacteristic RxChar = RxService.getCharacteristic(RXTX_CHAR_UUID);
if (RxChar == null) {
showMessage("Tx charateristic not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_UART);
return;
}
mBluetoothGatt.setCharacteristicNotification(RxChar,true);
BluetoothGattDescriptor descriptor = RxChar.getDescriptor(CCCD);
descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE );
mBluetoothGatt.writeDescriptor(descriptor);
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
/**
* Enable Notifications for the Battery service and Characteristic?
*/
BluetoothGattService batteryService = mBluetoothGatt.getService(BATTERY_SERVICE_UUID);
if (batteryService == null) {
showMessage("Battery service not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_BATTERY);
return;
}
BluetoothGattCharacteristic batteryChar = batteryService.getCharacteristic(BATTERY_CHAR_UUID);
if (batteryChar == null) {
showMessage("Battery charateristic not found!");
broadcastUpdate(DEVICE_DOES_NOT_SUPPORT_BATTERY);
return;
}
}
I was facing the same problem.
that's because when the device is sending the indicate value, your application is charged in another process and that's why you never get the indicate value which make the onCharacteristicChanged never fires.
to resolve your problem try to put all traitement in a service. and just call functions from your activity.
Device used for testing: Nexus 4, Android 4.3
Connection is working fine but the onCharacteristicChangedMethod of my callback is never called. However I am registering for notifications using setCharacteristicNotification(char, true) inside onServicesDiscovered and that function even returns true.
Device log (there are actually no messages at all when notifications should appear / are sent via the Bluetooth device):
07-28 18:15:06.936 16777-16809/de.ffuf.leica.sketch D/BluetoothGatt: setCharacteristicNotification() - uuid: 3ab10101-f831-4395-b29d-570977d5bf94 enable: true
07-28 18:15:06.936 4372-7645/com.android.bluetooth D/BtGatt.GattService: registerForNotification() - address=C9:79:25:34:19:6C enable: true
07-28 18:15:06.936 4372-7645/com.android.bluetooth D/BtGatt.btif: btif_gattc_reg_for_notification
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1018
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.GattService: onRegisterForNotifications() - address=null, status=0, registered=1, charUuid=3ab10101-f831-4395-b29d-570977d5bf94
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1016
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1018
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.GattService: onRegisterForNotifications() - address=null, status=0, registered=1, charUuid=3ab10102-f831-4395-b29d-570977d5bf94
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1016
07-28 18:15:06.946 4372-7684/com.android.bluetooth E/bt-btif: already has a pending command!!
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1013
07-28 18:15:06.946 4372-7684/com.android.bluetooth E/bt-btif: already has a pending command!!
07-28 18:15:06.946 4372-7645/com.android.bluetooth D/BtGatt.btif: btgattc_handle_event: Event 1013
07-28 18:15:06.946 4372-7684/com.android.bluetooth E/bt-btif: already has a pending command!!
07-28 18:15:06.976 4372-7645/com.android.bluetooth D/BtGatt.btif: btif_gattc_upstreams_evt: Event 9
GATT Notifications work fine using iOS and the app basically does the same as on Android (registering for notification etc.).
Has anyone else experienced this with a possible solution?
It seems like you forgot to write the Descriptor which tells your BLE device to go in this mode. See the code lines that deal with descriptor at http://developer.android.com/guide/topics/connectivity/bluetooth-le.html#notification
Without setting this descriptor, you never receive updates to a characteristic. Calling setCharacteristicNotification is not enough. This is a common mistake.
code snipped
protected static final UUID CHARACTERISTIC_UPDATE_NOTIFICATION_DESCRIPTOR_UUID = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb");
public boolean setCharacteristicNotification(BluetoothDevice device, UUID serviceUuid, UUID characteristicUuid,
boolean enable) {
if (IS_DEBUG)
Log.d(TAG, "setCharacteristicNotification(device=" + device.getName() + device.getAddress() + ", UUID="
+ characteristicUuid + ", enable=" + enable + " )");
BluetoothGatt gatt = mGattInstances.get(device.getAddress()); //I just hold the gatt instances I got from connect in this HashMap
BluetoothGattCharacteristic characteristic = gatt.getService(serviceUuid).getCharacteristic(characteristicUuid);
gatt.setCharacteristicNotification(characteristic, enable);
BluetoothGattDescriptor descriptor = characteristic.getDescriptor(CHARACTERISTIC_UPDATE_NOTIFICATION_DESCRIPTOR_UUID);
descriptor.setValue(enable ? BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE : new byte[] { 0x00, 0x00 });
return gatt.writeDescriptor(descriptor); //descriptor write operation successfully started?
}
#Boni2k - I have the same issues. In my case, I have 3 notifying characteristics and a handful of read/write characteristics.
What I did find is that there is some dependency between writeGattDescriptor and readCharacteristic. All of the writeGattDescriptors must come first and complete before you issue any readCharacteristic calls.
Here is my solution using Queues. Now I am getting notifications and everything else works fine:
Create two Queues like this:
private Queue<BluetoothGattDescriptor> descriptorWriteQueue = new LinkedList<BluetoothGattDescriptor>();
private Queue<BluetoothGattCharacteristic> characteristicReadQueue = new LinkedList<BluetoothGattCharacteristic>();
Then write all of your descriptors immediately after discovery with this method:
public void writeGattDescriptor(BluetoothGattDescriptor d){
//put the descriptor into the write queue
descriptorWriteQueue.add(d);
//if there is only 1 item in the queue, then write it. If more than 1, we handle asynchronously in the callback above
if(descriptorWriteQueue.size() == 1){
mBluetoothGatt.writeDescriptor(d);
}
}
and this callback:
public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
Log.d(TAG, "Callback: Wrote GATT Descriptor successfully.");
}
else{
Log.d(TAG, "Callback: Error writing GATT Descriptor: "+ status);
}
descriptorWriteQueue.remove(); //pop the item that we just finishing writing
//if there is more to write, do it!
if(descriptorWriteQueue.size() > 0)
mBluetoothGatt.writeDescriptor(descriptorWriteQueue.element());
else if(readCharacteristicQueue.size() > 0)
mBluetoothGatt.readCharacteristic(readQueue.element());
};
The method for reading a characteristic normally then looks like this:
public void readCharacteristic(String characteristicName) {
if (mBluetoothAdapter == null || mBluetoothGatt == null) {
Log.w(TAG, "BluetoothAdapter not initialized");
return;
}
BluetoothGattService s = mBluetoothGatt.getService(UUID.fromString(kYourServiceUUIDString));
BluetoothGattCharacteristic c = s.getCharacteristic(UUID.fromString(characteristicName));
//put the characteristic into the read queue
readCharacteristicQueue.add(c);
//if there is only 1 item in the queue, then read it. If more than 1, we handle asynchronously in the callback above
//GIVE PRECEDENCE to descriptor writes. They must all finish first.
if((readCharacteristicQueue.size() == 1) && (descriptorWriteQueue.size() == 0))
mBluetoothGatt.readCharacteristic(c);
}
and my read callback:
public void onCharacteristicRead(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
readCharacteristicQueue.remove();
if (status == BluetoothGatt.GATT_SUCCESS) {
broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
}
else{
Log.d(TAG, "onCharacteristicRead error: " + status);
}
if(readCharacteristicQueue.size() > 0)
mBluetoothGatt.readCharacteristic(readCharacteristicQueue.element());
}
When setting the value to the descriptor instead of putting descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE), put descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE). The callbacks for onCharacteristicChanged are called now.
I assume (you did not provide your source code) that you did not implement it as Google wanted:
(1)
mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
and then
(2)
BluetoothGattDescriptor descriptor = characteristic.getDescriptor(UUID.fromString(SampleGattAttributes.CLIENT_CHARACTERISTIC_CONFIG));
descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
mBluetoothGatt.writeDescriptor(descriptor);
I suppose 2 is missing. In that case I believe on low-level notification will be triggered but they will never be reported to application layer.
Experienced issues in earlier versions of Android receiving notifications (an indication that was registered) and always had a strange disconnect event afterwards. As it turns out, this was because we registered for notifications on five characteristics.
The error discovered in LogCat was:
02-05 16:14:24.990 1271-1601/? E/bt-btif﹕ Max Notification Reached, registration failed.
Prior to 4.4.2, the number of registrations was capped at 4! 4.4.2 increased this limit to 7.
By reducing the number of registrations in earlier versions, we were able to step around this limitation.
Well, this API name surely lead some confusions to app developer if he/she was not the Bluetooth background programmer.
From Bluetooth core specification perspective, quote from core spec 4.2 Vol 3, Part G section 3.3.3.3 "Client Characteristic Configuration" :
The characteristic descriptor value is a bit field. When a bit is set, that action shall be enabled, otherwise it will not be used.
and section 4.10
Notifications can be configured using the Client Characteristic Configuration descriptor (See Section 3.3.3.3).
which is clearly states that if client want to receive the notification(or indication,which need response) from server, should write the "Notification" bit to 1("Indication" bit also to 1 otherwise).
However, the name "setCharacteristicNotification" give us a hint is that if we set the parameters of this API as TURE, the client would got notifications; unfortunately this API only set the local bit to allow the notification sent to apps in case of remote notification comes. See code from Bluedroid:
/*******************************************************************************
**
** Function BTA_GATTC_RegisterForNotifications
**
** Description This function is called to register for notification of a service.
**
** Parameters client_if - client interface.
** bda - target GATT server.
** p_char_id - pointer to GATT characteristic ID.
**
** Returns OK if registration succeed, otherwise failed.
**
*******************************************************************************/
tBTA_GATT_STATUS BTA_GATTC_RegisterForNotifications (tBTA_GATTC_IF client_if,
BD_ADDR bda,
tBTA_GATTC_CHAR_ID *p_char_id)
{
tBTA_GATTC_RCB *p_clreg;
tBTA_GATT_STATUS status = BTA_GATT_ILLEGAL_PARAMETER;
UINT8 i;
if (!p_char_id)
{
APPL_TRACE_ERROR("deregistration failed, unknow char id");
return status;
}
if ((p_clreg = bta_gattc_cl_get_regcb(client_if)) != NULL)
{
for (i = 0; i < BTA_GATTC_NOTIF_REG_MAX; i ++)
{
if ( p_clreg->notif_reg[i].in_use &&
!memcmp(p_clreg->notif_reg[i].remote_bda, bda, BD_ADDR_LEN) &&
bta_gattc_charid_compare(&p_clreg->notif_reg[i].char_id, p_char_id))
{
APPL_TRACE_WARNING("notification already registered");
status = BTA_GATT_OK;
break;
}
}
if (status != BTA_GATT_OK)
{
for (i = 0; i < BTA_GATTC_NOTIF_REG_MAX; i ++)
{
if (!p_clreg->notif_reg[i].in_use)
{
memset((void *)&p_clreg->notif_reg[i], 0, sizeof(tBTA_GATTC_NOTIF_REG));
p_clreg->notif_reg[i].in_use = TRUE;
memcpy(p_clreg->notif_reg[i].remote_bda, bda, BD_ADDR_LEN);
p_clreg->notif_reg[i].char_id.srvc_id.is_primary = p_char_id->srvc_id.is_primary;
bta_gattc_cpygattid(&p_clreg->notif_reg[i].char_id.srvc_id.id, &p_char_id->srvc_id.id);
bta_gattc_cpygattid(&p_clreg->notif_reg[i].char_id.char_id, &p_char_id->char_id);
status = BTA_GATT_OK;
break;
}
}
if (i == BTA_GATTC_NOTIF_REG_MAX)
{
status = BTA_GATT_NO_RESOURCES;
APPL_TRACE_ERROR("Max Notification Reached, registration failed.");
}
}
}
else
{
APPL_TRACE_ERROR("Client_if: %d Not Registered", client_if);
}
return status;
}'
so what matters was the descriptor write action.
This one is working for me:
to notify master device that some characteristic is change, call this function on your pheripheral:
private BluetoothGattServer server;
//init....
//on BluetoothGattServerCallback...
//call this after change the characteristic
server.notifyCharacteristicChanged(device, characteristic, false);
in your master device: enable setCharacteristicNotification after discover the service:
#Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
super.onServicesDiscovered(gatt, status);
services = mGatt.getServices();
for(BluetoothGattService service : services){
if( service.getUuid().equals(SERVICE_UUID)) {
characteristicData = service.getCharacteristic(CHAR_UUID);
for (BluetoothGattDescriptor descriptor : characteristicData.getDescriptors()) {
descriptor.setValue( BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
mGatt.writeDescriptor(descriptor);
}
gatt.setCharacteristicNotification(characteristicData, true);
}
}
if (dialog.isShowing()){
mHandler.post(new Runnable() {
#Override
public void run() {
dialog.hide();
}
});
}
}
now you can check your characteristic value is change, for example onCharacteristicRead function (this also working on onCharacteristicChanged function as well) :
#Override
public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
Log.i("onCharacteristicRead", characteristic.toString());
byte[] value=characteristic.getValue();
String v = new String(value);
Log.i("onCharacteristicRead", "Value: " + v);
}
Here's a simple way to do it, but let me know if you see any drawbacks.
Step 1
Declare boolean variables
private boolean char_1_subscribed = false;
private boolean char_2_subscribed = false;
private boolean char_3_subscribed = false;
Step 2
subscribe to the first characteristic in the onServicesDiscovered callback:
#Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED);
} else {
Log.w(TAG, "onServicesDiscovered received: " + status);
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
if(!char_1_subscribed)
subscribeToNotification(gatt.getService(UUID_SERVICE).getCharacteristic(UUID_CHAR_1)); char_1_subscribed = true;
}
Step 3
Subscribe to any others after the onCharacteristicChanged callback fires
#Override
public void onCharacteristicChanged(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic) {
if(UUID_CHAR_1.equals(characteristic.getUuid()))
{
if(!char_1_subscribed)
subscribeToNotification(gatt.getService(UUID_SERVICE).getCharacteristic(UUID_CHAR_2)); char_2_subscribed = true;
}
if(UUID_CHAR_2.equals(characteristic.getUuid()))
{
if(!char_3_subscribed)
subscribeToNotification(gatt.getService(UUID_SERVICE).getCharacteristic(UUID_CHAR_3)); char_3_subscribed = true;
}
}
I had another reason that I would like to add as it drove me crazy the whole day:
On my Samsung Note 3 I did not receive notifications of changed values while the same code worked on any other device I tested with.
Rebooting the device solved all the problems. Obvious, but when you are in the problem, you forget to think of.
I've experienced the problems with notifications for BLE on Android as well. However there's a fully working demo that includes a bluetooth wrapper around BluetoothAdapter. The wrapper is called BleWrapper and ships with the demo application called BLEDemo contained in the Application Accelerator package. Download here: https://developer.bluetooth.org/Pages/Bluetooth-Android-Developers.aspx. You need to register with your email address at the top right before downloading. The project's license allows for free use, code modification and publication.
To my experience the Android demo application handles BLE notification subscriptions very well. I've not yet dived too much into the code to see how the wrapper actually wraps.
There's an Android app available in Play Store that is a customization of the Application accelerator demo. As the user interface looks nearly the same I suppose that it also uses BleWrapper. Download the app here: https://play.google.com/store/apps/details?id=com.macdom.ble.blescanner