RxAndroidBle

Introduction

RxAndroidBle is a powerful painkiller for Android's Bluetooth Low Energy headaches. It is backed by RxJava, implementing complicated APIs as handy reactive observables. The library does for you:

• Fancy asynchronous operations support (read, write, notifications)
• Threading management in order to meet Android contracts
• Connection and operation error handling

For support head to StackOverflow #rxandroidble

Read the official announcement at Polidea Blog.

RxAndroidBLE @ Mobile Central Europe 2016

Usage

Obtaining the client

It's your job to maintain single instance of the client. You can use singleton, scoped Dagger component or whatever else you want.

RxBleClient rxBleClient = RxBleClient.create(context);

Turning the bluetooth on / off

The library does not handle managing the state of the BluetoothAdapter.
Direct managing of the state is not recommended as it violates the application user's right to manage the state of their phone. See Javadoc of BluetoothAdapter.enable() method.
It is the user's responsibility to inform why the application needs Bluetooth to be turned on and for ask the application's user consent.
It is possible to show a native activity for turning the Bluetooth on by calling:

Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
 int REQUEST_ENABLE_BT = 1; context.startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);

Device discovery

Scanning devices in the area is simple as that:

Subscription scanSubscription = rxBleClient.scanBleDevices(

new ScanSettings.Builder()

 // .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY) // change if needed

 // .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES) // change if needed

 .build()

// add filters if needed )
  .subscribe(

scanResult -> {

 // Process scan result here.

}
,

throwable -> {

 // Handle an error here.

}

  );
  // When done, just unsubscribe. scanSubscription.unsubscribe();

For devices with API <21 (before Lollipop) the scan API is emulated to get the same behaviour.

Observing client state

On Android it is not always trivial to determine if a particular BLE operation has a potential to succeed. i.e. to scan on Android 6.0 the device needs to have a BluetoothAdapter, the application needs to have a granted permission to use either ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION and Location Services needs to be turned on. To be sure that the scan will work only when everything is ready you could use:

Subscription flowSubscription = rxBleClient.observeStateChanges()
  .switchMap(state -> {
 // switchMap makes sure that if the state will change the rxBleClient.scanBleDevices() will unsubscribe and thus end the scan

switch (state) {

  case READY:

  // everything should work

  return rxBleClient.scanBleDevices();

 case BLUETOOTH_NOT_AVAILABLE:

  // basically no functionality will work here

 case LOCATION_PERMISSION_NOT_GRANTED:

  // scanning and connecting will not work

 case BLUETOOTH_NOT_ENABLED:

  // scanning and connecting will not work

 case LOCATION_SERVICES_NOT_ENABLED:

  // scanning will not work

 default:

  return Observable.empty();

}

  
}
)
  .subscribe(

rxBleScanResult -> {

 // Process scan result here.

}
,

throwable -> {

 // Handle an error here.

}

  );

// When done, just unsubscribe. flowSubscription.unsubscribe();

Connection

For further BLE interactions the connection is required.

String macAddress = "AA:BB:CC:DD:EE:FF"; RxBleDevice device = rxBleClient.getBleDevice(macAddress);
  Subscription subscription = device.establishConnection(false) // <-- autoConnect flag
  .subscribe(

rxBleConnection -> {

 // All GATT operations are done through the rxBleConnection.

}
,

throwable -> {

 // Handle an error here.

}

  );
  // When done... unsubscribe and forget about connection teardown :) subscription.unsubscribe();

Auto connect

From BluetoothDevice.connectGatt() Javadoc:

autoConnect boolean: Whether to directly connect to the remote device (false) or to automatically connect as soon as the remote device becomes available (true).

Auto connect concept may be misleading at first glance. With the autoconnect flag set to false the connection will end up with an error if a BLE device is not advertising when the RxBleDevice#establishConnection method is called. From platform to platform timeout after which the error is emitted differs, but in general it is rather tens of seconds than single seconds (~30 s).

Setting the auto connect flag to true allows you to wait until the BLE device becomes discoverable. The RxBleConnection instance won't be emitted until the connection is fully set up. From experience it also handles acquiring wake locks, so it's safe to assume that your Android device will be woken up after the connection has been established - but it is not a documented feature and may change in the future system releases.

Be careful not to overuse the autoConnect flag. On the other side it has negative impact on the connection initialization speed. Scanning window and interval is lowered as it is optimized for background use and depending on Bluetooth parameters it may (and usually do) take more time to establish the connection.

Read / write operations

Read

device.establishConnection(false)
  .flatMap(rxBleConnection -> rxBleConnection.readCharacteristic(characteristicUUID))
  .subscribe(

characteristicValue -> {

 // Read characteristic value.

}
,

throwable -> {

 // Handle an error here.

}

  );

Write

device.establishConnection(false)
  .flatMap(rxBleConnection -> rxBleConnection.writeCharacteristic(characteristicUUID, bytesToWrite))
  .subscribe(

characteristicValue -> {

 // Characteristic value confirmed.

}
,

throwable -> {

 // Handle an error here.

}

  );

Multiple reads

device.establishConnection(false)
  .flatMap(rxBleConnection -> Observable.combineLatest(

rxBleConnection.readCharacteristic(firstUUID),

rxBleConnection.readCharacteristic(secondUUID),

YourModelCombiningTwoValues::new
  ))
  .subscribe(

model -> {

 // Process your model.

}
,

throwable -> {

 // Handle an error here.

}

  );

Long write

device.establishConnection(false)
  .flatMap(rxBleConnection -> rxBleConnection.createNewLongWriteBuilder()

.setCharacteristicUuid(uuid) // required or the .setCharacteristic()

// .setCharacteristic() alternative if you have a specific BluetoothGattCharacteristic

.setBytes(byteArray)

// .setMaxBatchSize(maxBatchSize) // optional -> default 20 or current MTU

// .setWriteOperationAckStrategy(ackStrategy) // optional to postpone writing next batch

.build()
  )
  .subscribe(

byteArray -> {

 // Written data.

}
,

throwable -> {

 // Handle an error here.

}

  );

Read and write combined

device.establishConnection(false)
  .flatMap(rxBleConnection -> rxBleConnection.readCharacteristic(characteristicUuid)

.doOnNext(bytes -> {

 // Process read data.

}
)

.flatMap(bytes -> rxBleConnection.writeCharacteristic(characteristicUuid, bytesToWrite))
  )
  .subscribe(

writeBytes -> {

 // Written data.

}
,

throwable -> {

 // Handle an error here.

}

  );

Change notifications

device.establishConnection(false)
  .flatMap(rxBleConnection -> rxBleConnection.setupNotification(characteristicUuid))
  .doOnNext(notificationObservable -> {

// Notification has been set up
  
}
)
  .flatMap(notificationObservable -> notificationObservable) // <-- Notification has been set up, now observe value changes.
  .subscribe(

bytes -> {

 // Given characteristic has been changes, here is the value.

}
,

throwable -> {

 // Handle an error here.

}

  );

Observing connection state

If you want to observe changes in device connection state just subscribe like below. On subscription you will receive the most current state instantly.

device.observeConnectionStateChanges()
  .subscribe(

connectionState -> {

 // Process your way.

}
,

throwable -> {

 // Handle an error here.

}

  );

Logging

For connection debugging you can use extended logging

RxBleClient.setLogLevel(RxBleLog.DEBUG);

By default RxBleLog uses logcat to print the messages. You can provide your own logger implementation to forward it to other logging libraries such as Timber.

RxBleLog.setLogger((level, tag, msg) -> Timber.tag(tag).log(level, msg));

Error handling

Every error you may encounter is provided via onError callback. Each public method has JavaDoc explaining possible errors.

Important — Prior to version 1.3.0 each failure on BluetoothGatt was effectively closing the connection. From 1.3.0 onwards individual errors will not close the connection if they are not directly related to it. This change does allow to retry operations (i.e. after Android will establish a device bond).

Observable behaviour

From different interfaces, you can obtain different Observables which exhibit different behaviours. There are three types of Observables that you may encounter.

1. Single value, completing — i.e. RxBleConnection.readCharacteristic(), RxBleConnection.writeCharacteristic(), etc.
2. Multiple values, not completing - i.e. RxBleClient.scan(), RxBleDevice.observeConnectionStateChanges() and Observable emitted by RxBleConnection.setupNotification() / RxBleConnection.setupIndication()
3. Single value, not completing — these usually are meant for auto cleanup upon unsubscribing i.e. setupNotification() / setupIndication() — when you will unsubscribe the notification / indication will be disabled

RxBleDevice.establishConnection() is an Observable that will emit a single RxBleConnection but will not complete as the connection may be later a subject to an error (i.e. external disconnection). Whenever you are no longer interested in keeping the connection open you should unsubscribe from it which will cause disconnection and cleanup of resources.

The below table contains an overview of used Observable patterns

* this Observable when unsubscribed closes/cleans up internal resources (i.e. finishes scan, closes a connection, disables notifications)
** this Observable does emit only a single value and finishes in exactly one situation — when Bluetooth Adapter is not available on the device. There is no reason to monitor other states as the adapter does not appear during runtime.

Helpers

We encourage you to check the package com.polidea.rxandroidble.helpers which contains handy reactive wrappers for some typical use-cases.

Value interpretation

Bluetooth Specification specifies formats in which int/ float/ String values may be stored in characteristics. BluetoothGattCharacteristic has functions for retrieving those ( .getIntValue()/ .getFloatValue()/ .getStringValue()). Since RxAndroidBle reads and notifications emit byte[] you may want to use ValueIntepreter helper to retrieve the same data easily.

Observing BluetoothAdapter state

If you would like to observe BluetoothAdapter state changes you can use RxBleAdapterStateObservable.

Permissions

RxAndroidBle already provides all the necessary bluetooth permissions for you. Recently, Google has started checking these when releasing to the Play Store. If you have ACCESS_COARSE_LOCATION set manually you may run into an issue where your permission do not merge with RxAndroidBle's, resulting in a failure to upload to the Play Store This permission is only required on SDK 23+. If you need this permission on a lower version of Android use:

<uses-permission
android:name="android.permission.ACCESS_COARSE_LOCATION"
android:maxSdkVersion="22"/>

More examples

Complete usage examples are located in /sample GitHub repo.

Download

Gradle

compile "com.polidea.rxandroidble:rxandroidble:1.4.2"

Maven

<dependency>
<groupId>com.polidea.rxandroidble</groupId>
<artifactId>rxandroidble</artifactId>
<version>1.4.2</version>
<type>aar</type> </dependency>

Snapshot

If your are interested in cutting-edge build you can get a SNAPSHOT version of the library. NOTE: It is built from the top of the master branch and a subject to more frequent changes that may break the API and/or change behavior.

To be able to download it you need to add Sonatype Snapshot repository site to your build.gradle file:

maven {
 url "https://oss.sonatype.org/content/repositories/snapshots" 
}

Unit testing

Using RxAndroidBle enables you to unit test your application easily. For examples how to use mocking head to MockRxAndroidBle.

Note: Using MockRxAndroidBle in unit tests needs Robolectric.

Small performance comparison

Contributing

If you would like to contribute code you can do so through GitHub by forking the repository and sending a pull request.

When submitting code, please make every effort to follow existing conventions and style in order to keep the code as readable as possible. Please also make sure your code compiles by running ./gradlew clean checkstyle test.

Support

• non-commercial — head to StackOverflow #rxandroidble
• commercial — drop an email to [email protected] for more info

Maintainers

• Dariusz Seweryn ( [email protected])
• Pawe? Urban ( [email protected])

Contributors, thank you!

License

Copyright 2016 Polidea Sp. z o.o  Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License. You may obtain a copy of the License at
  http://www.apache.org/licenses/LICENSE-2.0  Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. 

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