Functional Bluetooth GATT This library allows easy and safer usage of BluetoothGatt in Android. Instead of having callbacks to manage, you just need to call functions. It has also been tested successfully on Wear OS, with the sample included in this repository. It should work similarly on other Android variants such as Android TV.
It does so by taking advantage of the excellent coroutines feature in the Kotlin programming language that allows to write asynchronous code in a sequential/synchronous style, which means, without the callback hell, and without blocking any thread (which would waste memory and decrease performances).
This library makes it possible to have readable and debuggable code that interacts with Bluetooth Low Energy GATT (General Attribute), that is, the connection part of the Bluetooth Low Energy standard.
As we needed to have an Android app interact with a Bluetooth Low Energy device, we found the Android BluetoothGatt API and a few RxJava libraries built on top of it.
Unfortunately, none suited our needs:
- The vanilla Android BluetoothGatt API is extremely hard to get right,
because you have to provide a single instance of what we call a "God
Callback", that is, an instance of a class with overridable methods that
asynchronously receive the results off all operations of a given type (for
example, the result of a characteristic you requested to read, or the result
of whether a characteristic write went well or failed. You're on your own to
make readable code with this, where unrelated characteristic reads, writes
or other operation types are dispatched in the same callback method (like
onCharacteristicRead(…)). - The RxJava libraries would mean we'd have to learn RxJava, which is known to have a steep learning curve, steeper than learning another programming language like Kotlin from Java experience, and steeper than learning Kotlin plus coroutines. Also, RxJava is a big library, even bigger if you have to use both version 1 and version 2 in the same project. RxJava2 methods count is higher than the sum of Kotlin's stdlib and kotlinx.coroutines.
We are expecting to make a few API changes based on your feedback and real world usages to improve this library. You can help by sharing your experience or feedback in the issues having a green "help wanted" tag.
Since the API design it not final at the moment, we're very open to feedback while you're using this library.
Please, open an issue if something can be improved. If you just want to tell the author what you're doing with this library, feel free to reach out via Twitter DM, public tweet.
You can also join the discussion on Kotlin's Slack in the #beepiz-libraries channel (you can get an invitation here).
As usual, scan BLE devices using BluetoothLeScanner to find you
BluetoothDevice, or create an instance from the MAC address of your target
device.
With this BluetoothDevice instance, you can create a GattConnection
object, which will be key to perform Bluetooth GATT operations using
coroutines.
On this GattConnection object, call connect() to initiate the connection. Immediately after
It will suspend until the connection is established, then you use the
connection:
The currently supported GATT operations on the GattConnection class are:
- Services discovery, using
discoverServices()which returns and cache the list of the services on the connected device. - Characteristic read, using
readCharacteristic(…). Services discovery has to be completed before, as usual. - Characteristic write, using
writeCharacteristic(…). Services discovery has to be completed before, as usual. - ReliableWrite, with
reliableWrite { … }. Implemented, but could not be tested yet. Open an issue if your device supports it - Descriptor read, using
readDescriptor(…). Services discovery has to be completed before, as usual. - Descriptor write, using
writeDescriptor(…). Services discovery has to be completed before, as usual. - RSSI read, using
readRemoteRssi(…). - NOTIFY characteristics with the
notifyChannel. These haven't been tested yet. Feedback wanted. - Toggling characteristic update notifications with
setCharacteristicNotificationsEnabled(…). Tied to NOTIFY feature. - PHY, using
readPhy(). Only supported in Android O. Has not been tested. We don't know what this is either, to be honest.
When you're done with the BLE device (you need to be done before the
device's battery runs out, unless you're dealing with an always on wearable
that the user didn't disconnect), call close().
If you want to reconnect within seconds, or a few minutes to the same device,
you can call disconnect() instead, which will allow to call connect()
again later.
Here's a basic example that just logs the characteristics (using
the print() method defined here
):
suspend fun BluetoothDevice.logGattServices(tag: String = "BleGattCoroutines") {
val deviceConnection = GattConnection(bluetoothDevice = this@logGattServices)
try {
deviceConnection.connect() // Suspends until connection is established
val gattServices = deviceConnection.discoverServices() // Suspends until completed
gattServices.forEach {
it.characteristics.forEach {
try {
deviceConnection.readCharacteristic(it) // Suspends until characteristic is read
} catch (e: Exception) {
Log.e(tag, "Couldn't read characteristic with uuid: ${it.uuid}", e)
}
}
Log.d(tag, it.print(printCharacteristics = true))
}
} finally {
deviceConnection.close() // Close when no longer used. Also triggers disconnect by default.
}
}The snippet below is the example you can find in the sample, powered by two
extension methods for brevity (deviceFor(…) and useBasic { device, services -> … }). It also uses the GenericAccess object, which is the
definition of the standard Bluetooth GATT "Generic access". It includes
extension functions and properties for easy and readable usage. You can
write a similar specification for any BLE device or BluetoothGattService
you want.
private val myEddystoneUrlBeaconMacAddress = "F2:D6:43:93:70:7A"
private val defaultDeviceMacAddress = myEddystoneUrlBeaconMacAddress
suspend fun logNameAndAppearance(deviceMacAddress: String = defaultDeviceMacAddress) {
deviceFor(deviceMacAddress).useBasic { device, services ->
services.forEach { Timber.d("Service found with UUID: ${it.uuid}") }
with(GenericAccess) {
device.readAppearance()
Timber.d("Device appearance: ${device.appearance}")
device.readDeviceName()
Timber.d("Device name: ${device.deviceName}")
}
}
}When connected to my Google Beacon, the code above outputs the following in logcat:
I/MainViewModel$logNameAndAppearance: Connected!
I/MainViewModel$logNameAndAppearance: Services discovered!
D/MainViewModel$logNameAndAppearance: Service found with UUID: 00001800-0000-1000-8000-00805f9b34fb
D/MainViewModel$logNameAndAppearance: Service found with UUID: 00001801-0000-1000-8000-00805f9b34fb
D/MainViewModel$logNameAndAppearance: Service found with UUID: ee0c2080-8786-40ba-ab96-99b91ac981d8
D/MainViewModel$logNameAndAppearance: Device appearance: 512
D/MainViewModel$logNameAndAppearance: Device name: eddystone Config
I/MainViewModel$logNameAndAppearance: Disconnected!
I/MainViewModel$logNameAndAppearance: Closed!This proves our library is working and that Bluetooth GATT can be functional.
BleGattCoroutines is published on MavenCentral.
The following artifacts are published, use the ones you need:
implementation("com.beepiz.blegattcoroutines:blegattcoroutines-core:0.5.0")
implementation("com.beepiz.blegattcoroutines:blegattcoroutines-genericaccess:0.5.0")Let's say you need a new feature or a fix that did not make it to a release yet:
You can grab it in the latest dev version by adding the corresponding repository and
changing the library version to the dev version you need in your root project build.gradle file:
repositories {
google()
mavenCentral()
// Add the repo below:
maven(url = "https://s01.oss.sonatype.org/content/repositories/snapshots") {
mavenContent {
includeGroup("com.beepiz.blegattcoroutines")
snapshotsOnly()
}
}
}
// Switch the version to a snapshot
implementation("com.beepiz.blegattcoroutines:blegattcoroutines-core:0.5.1-SNAPSHOT")
implementation("com.beepiz.blegattcoroutines:blegattcoroutines-genericaccess:0.5.1-SNAPSHOT")Releases are announced on GitHub, you can subscribe byclicking on "Watch", then "Custom", then check "Releases".