Android BLE Library

An Android library that solves a lot of Android's Bluetooth Low Energy problems. The BleManager class exposes high level API for connecting and communicating with Bluetooth LE peripherals. The API is clean and easy to read.

Features

BleManager class provides the following features:

1. Connection, with automatic retries
2. Service discovery
3. Bonding (optional) and removing bond information (using reflections)
4. Automatic handling of Service Changed indications
5. Device initialization
6. Asynchronous and synchronous BLE operations using queue
7. Splitting and merging long packets when writing and reading characteristics and descriptors
8. Requesting MTU and connection priority (on Android Lollipop or newer)
9. Reading and setting preferred PHY (on Android Oreo or newer)
10. Reading RSSI
11. Refreshing device cache (using reflections)
12. Reliable Write support
13. Operation timeouts (for connect, disconnect and wait for notification requests)
14. Error handling
15. Logging
16. GATT server (since version 2.2)

The library does not provide support for scanning for Bluetooth LE devices. For scanning, we recommend using Android Scanner Compat Library which brings almost all recent features, introduced in Lollipop and later, to the older platforms.

Version 2.2

New features added in version 2.2:

1. GATT Server support. This includes setting up the local GATT server on the Android device, new requests for server operations:
   • wait for read,
   • wait for write,
   • send notification,
   • send indication,
   • set characteristic value,
   • set descriptor value.
2. New conditional requests:
   • waif if,
   • wait until.
3. BLE operations are no longer called from the main thread.
4. There's a new option to set a handler for invoking callbacks. A handler can also be set per-callback.

Migration to version 2.2

Version 2.2 breaks some API known from version 2.1.1. Check out migration guide.

Importing

Maven Central or jcenter

The library may be found on jcenter and Maven Central repository. Add it to your project by adding the following dependency:

implementation 'no.nordicsemi.android:ble:2.2.4'

The last version not migrated to AndroidX is 2.0.5.

To import the BLE library with set of parsers for common Bluetooth SIG characteristics, use:

implementation 'no.nordicsemi.android:ble-common:2.2.4'

For more information, read this.

An extension for easier integration with LiveData is available after adding:

implementation 'no.nordicsemi.android:ble-livedata:2.2.4'

This extension adds ObservableBleManager with state and bondingState properties, which notify about connection and bond state using androidx.lifecycle.LiveData.

As a library module

Clone this project and add ble module as a dependency to your project:

1. In settings.gradle file add the following lines:

include ':ble'
project(':ble').projectDir = file('../Android-BLE-Library/ble')

2. In app/build.gradle file add implementation project(':ble') inside dependencies.
3. Sync project and build it.

You may do the same with other modules available in this project. Keep in mind, that ble-livedata module requires Kotlin, but no special changes are required in the app.

Setting up

The library uses Java 1.8 features. Make sure your build.gradle includes the following configuration:

 compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
// For Kotlin projects additionally:
kotlinOptions {
jvmTarget ="1.8"
}

Usage

A BleManager instance is responsible for connecting and communicating with a single peripheral. Multiple manager instances are allowed. Extend BleManager with you manager where you define the high level device's API.

BleManager may be used in different ways:

1. In a Service, for a single connection - see nRF Toolbox -> RSC profile,
2. In a Service with multiple connections - see nRF Toolbox -> Proximity profile,
3. From ViewModel's repo - see Architecture Components and nRF Blinky,
4. As a singleton - not recommended, see nRF Toolbox -> HRM.

The first step is to create your BLE Manager implementation, like below. The manager should act as API of your remote device, to separate lower BLE layer from the application layer.

classMyBleManagerextendsBleManager {
finalstaticUUIDSERVICE_UUID = UUID.fromString("XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX");
finalstaticUUIDFIRST_CHAR = UUID.fromString("XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX");
finalstaticUUIDSECOND_CHAR = UUID.fromString("XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX");
// Client characteristicsprivateBluetoothGattCharacteristicfirstCharacteristic, secondCharacteristic;
MyBleManager(@NonNullfinalContextcontext) {
super(context);
}
@NonNull@OverrideprotectedBleManagerGattCallbackgetGattCallback() {
returnnewMyManagerGattCallback();
}
@Overridepublicvoidlog(finalintpriority, @NonNullfinalStringmessage) {
if (Build.DEBUG || priority == Log.ERROR) {
Log.println(priority, "MyBleManager", message);
}
}
/** * BluetoothGatt callbacks object. */privateclassMyManagerGattCallbackextendsBleManagerGattCallback {
// This method will be called when the device is connected and services are discovered.// You need to obtain references to the characteristics and descriptors that you will use.// Return true if all required services are found, false otherwise.@OverridepublicbooleanisRequiredServiceSupported(@NonNullfinalBluetoothGattgatt) {
finalBluetoothGattServiceservice = gatt.getService(SERVICE_UUID);
if (service != null) {
firstCharacteristic = service.getCharacteristic(FIRST_CHAR);
secondCharacteristic = service.getCharacteristic(SECOND_CHAR);
}
// Validate propertiesbooleannotify = false;
if (firstCharacteristic != null) {
finalintproperties = dataCharacteristic.getProperties();
notify = (properties & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0;
}
booleanwriteRequest = false;
if (secondCharacteristic != null) {
finalintproperties = controlPointCharacteristic.getProperties();
writeRequest = (properties & BluetoothGattCharacteristic.PROPERTY_WRITE) != 0;
secondCharacteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);
}
// Return true if all required services have been foundreturnfirstCharacteristic != null && secondCharacteristic != null
&& notify && writeRequest;
}
// If you have any optional services, allocate them here. Return true only if// they are found. @OverrideprotectedbooleanisOptionalServiceSupported(@NonNullfinalBluetoothGattgatt) {
returnsuper.isOptionalServiceSupported(gatt);
}
// Initialize your device here. Often you need to enable notifications and set required// MTU or write some initial data. Do it here.@Overrideprotectedvoidinitialize() {
// You may enqueue multiple operations. A queue ensures that all operations are // performed one after another, but it is not required.beginAtomicRequestQueue()
.add(requestMtu(247) // Remember, GATT needs 3 bytes extra. This will allow packet size of 244 bytes.
.with((device, mtu) -> log(Log.INFO, "MTU set to " + mtu))
.fail((device, status) -> log(Log.WARN, "Requested MTU not supported: " + status)))
.add(setPreferredPhy(PhyRequest.PHY_LE_2M_MASK, PhyRequest.PHY_LE_2M_MASK, PhyRequest.PHY_OPTION_NO_PREFERRED)
.fail((device, status) -> log(Log.WARN, "Requested PHY not supported: " + status)))
.add(enableNotifications(firstCharacteristic))
.done(device -> log(Log.INFO, "Target initialized"))
.enqueue(); // You may easily enqueue more operations here like such:writeCharacteristic(secondCharacteristic, "Hello World!".getBytes())
.done(device -> log(Log.INFO, "Greetings sent"))
.enqueue();
// Set a callback for your notifications. You may also use waitForNotification(...).// Both callbacks will be called when notification is received.setNotificationCallback(firstCharacteristic, callback);
// If you need to send very long data using Write Without Response, use split()// or define your own splitter in split(DataSplitter splitter, WriteProgressCallback cb). writeCharacteristic(secondCharacteristic, "Very, very long data that will no fit into MTU")
.split()
.enqueue();
}
@OverrideprotectedvoidonDeviceDisconnected() {
// Device disconnected. Release your references here.firstCharacteristic = null;
secondCharacteristic = null;
}
}
// Define your API.privateabstractclassFluxHandlerimplementsProfileDataCallback { @OverridepublicvoidonDataReceived(@NonNullfinalBluetoothDevicedevice, @NonNullfinalDatadata) {
// Some validation?if (data.size() != 1) {
onInvalidDataReceived(device, data);
return;
}
onFluxCapacitorEngaged();
}
abstractvoidonFluxCapacitorEngaged();
}
/** Initialize time machine. */publicvoidenableFluxCapacitor(finalintyear) {
waitForNotification(firstCharacteristic)
.trigger(
writeCharacteristic(secondCharacteristic, newFluxJumpRequest(year))
.done(device -> log(Log.INDO, "Power on command sent"))
)
.with(newFluxHandler() {
publicvoidonFluxCapacitorEngaged() {
log(Log.WARN, "Flux Capacitor enabled! Going back to the future in 3 seconds!");
sleep(3000).enqueue();
write(secondCharacteristic, "Hold on!".getBytes())
.done(device -> log(Log.WARN, "It's " + year + "!"))
.fail((device, status) -> "Not enough flux? (status: " + status + ")")
.enqueue();
}
})
.enqueue();
}
/**  * Aborts time travel. Call during 3 sec after enabling Flux Capacitor and only if you don't  * like 2020.  */publicvoidabort() {
cancelQueue();
}
}

To connect to a Bluetooth LE device using GATT, create a manager instance:

classMyRepoimplementsConnectionObserver {
privateMyBleManagermanager;
// [...]voidconnect(@NonNullfinalBluetoothDevicedevice) {
manager = newMyBleManager(context);
manager.setConnectionObserver(this);
manager.connect(device)
.timeout(100000)
.retry(3, 100)
.done(device -> Log.i(TAG, "Device initiated"))
.enqueue();
}
// [...]
}

Adding GATT Server support

Starting from version 2.2 you may now define and use the GATT server in the BLE Library.

First, override a BleServerManager class and override initializeServer() method. Some helper methods, like characteristic(...), descriptor(...) and their shared counterparts were created for making the initialization more readable.

publicclassServerManagerextendsBleServerManager {
ServerManager(@NonNullfinalContextcontext) {
super(context);
}
@NonNull@OverrideprotectedList<BluetoothGattService> initializeServer() {
// In this example there's only one service, so singleton list is created.returnCollections.singletonList(
service(SERVICE_UUID,
characteristic(CHAR_UUID,
BluetoothGattCharacteristic.PROPERTY_WRITE// properties
| BluetoothGattCharacteristic.PROPERTY_NOTIFY
| BluetoothGattCharacteristic.PROPERTY_EXTENDED_PROPS,
BluetoothGattCharacteristic.PERMISSION_WRITE, // permissionsnull, // initial datacccd(), reliableWrite(), description("Some description", false) // descriptors
))
);
}
}

Instantiate the server and set the callback listener:

classMyRepoimplementsServerObserver {
privateServerManagerserverManager;
// [...]voidinit() {
serverManager = newServerManager(context);
serverManager.setServerObserver(this);
}
// [...]
}

Set the server manager for each client connection:

classMyRepoimplementsConnectionObserver, BondingObserver {
privateServerManagerserverManager;
privateMyBleManagermanager;
// [...]// This method may be called from e.g. // ServerObserver#onDeviceConnectedToServer(@NonNull final BluetoothDevice device)voidconnect(@NonNullfinalBluetoothDevicedevice) {
manager = newMyBleManager(context);
manager.setConnectionObserver(this);
manager.setBondingObserver(this);
// Use the manager with the server.manager.useServer(serverManager);
manager.connect(device)
// [...]
.enqueue();
}
// [...]
}

The ServerObserver.onServerReady() will be invoked when all service were added. You may initiate your connection there.

In your client manager class, override the following method:

classMyBleManagerextendsBleManager {
// [...]	// Server characteristicsprivateBluetoothGattCharacteristicserverCharacteristic;
// [...]/** * BluetoothGatt callbacks object. */privateclassMyManagerGattCallbackextendsBleManagerGattCallback {
// [...]	@OverrideprotectedvoidonServerReady(@NonNullfinalBluetoothGattServerserver) {
// Obtain your server attributes.serverCharacteristic = server
.getService(SERVICE_UUID)
.getCharacteristic(CHAR_UUID);
// Set write callback, if you need. It will be called when the remote device writes// something to the given server characteristic.setWriteCallback(serverCharacteristic)
.with((device, data) ->
sendNotification(otherCharacteristic, "any data".getBytes())
.enqueue()
);
}
// [...]@OverrideprotectedvoidonDeviceDisconnected() {
// [...]serverCharacteristic = null;
}
}
// [...]
}

Examples

Find the simple example here Android nRF Blinky.

For an example how to use it from an Activity or a Service, check the base Activity and Service classes in nRF Toolbox.

Version 1.x

The BLE library v 1.x is no longer supported. Please migrate to 2.2+ for bug fixing releases. Find it on version/1x branch.

Migration guide is available here.