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.
The first step is to include RxAndroidBle into your project.
If you use Gradle to build your project — as a Gradle project implementation dependency:
implementation "com.polidea.rxandroidble2:rxandroidble:1.13.0"If you use Maven to build your project — as a Maven project dependency:
<dependency>
<groupId>com.polidea.rxandroidble2</groupId>
<artifactId>rxandroidble</artifactId>
<version>1.13.0</version>
<type>aar</type>
</dependency>If your are interested in cutting-edge build you can get a x.y.z-SNAPSHOT version of the library.
NOTE: Snapshots are built from the top of the master and develop branches 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" }Android since API 23 (6.0 / Marshmallow) requires additional permissions declared in the manifest for an app to run a BLE scan. RxAndroidBle provides minimal required bluetooth permissions for you in AndroidManifest — it assumes to be used in the foreground and not deriving actual user location from BLE signal.
Runtime permissions required for running a BLE scan:
| from API | to API (inclusive) | Acceptable runtime permissions |
|---|---|---|
| 18 | 22 | (No runtime permissions needed) |
| 23 | 28 | One of below: - android.permission.ACCESS_COARSE_LOCATION- android.permission.ACCESS_FINE_LOCATION |
| 29 | 30 | - android.permission.ACCESS_FINE_LOCATION- android.permission.ACCESS_BACKGROUND_LOCATION* |
| 31 | current | - android.permission.BLUETOOTH_SCAN**- android.permission.ACCESS_FINE_LOCATION*** |
* Needed if scan is performed in background
** It is assumed in AndroidManifest that the application is trying to derive user's location from BLE signal. If that is not the case look below into Potential permission issues.
*** Needed if BLUETOOTH_SCAN is not using neverForLocation flag
Runtime permissions required for connecting to a BLE peripheral:
| from API | to API (inclusive) | Acceptable runtime permissions |
|---|---|---|
| 18 | 30 | (No runtime permissions needed) |
| 31 | current | - android.permission.BLUETOOTH_CONNECT |
Google is checking AndroidManifest for declaring permissions when releasing to the Play Store. If you have ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION set manually using tag uses-permission (as opposed to uses-permission-sdk-23) you may run into an issue where your manifest does not merge with RxAndroidBle's AndroidManifest.xml, resulting in a failure to upload to the Play Store. These permissions are required only on APIs 23-30 assuming your app is not accessing location otherwise. If you need any of these permissions other versions of Android replace your statement with:
<uses-permission-sdk-23 android:name="android.permission.ACCESS_FINE_LOCATION" tools:node="remove" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />If you only want to scan BLE peripherals and do not access location otherwise you can restrict location permissions to only the required range by using Manifest Merger tool directives:
<uses-permission-sdk-23 android:name="android.permission.ACCESS_COARSE_LOCATION" tools:node="remove" />
<uses-permission-sdk-23 android:name="android.permission.ACCESS_FINE_LOCATION" tools:node="remove" />
<uses-permission-sdk-23 android:name="android.permission.ACCESS_FINE_LOCATION" android:maxSdkVersion="30" />After API 31 (Android 12) there are new Bluetooth permissions. One of them comes in a flavour that restricts deriving user's location from BLE signal acquired while scanning — this is assumed by the library. If you need to locate user by scanning BLE use below but keep in mind that you will still need ACCESS_FINE_LOCATION then:
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" tools:node="remove" />
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />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);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);Scanning devices in the area is simple as that:
Disposable 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 dispose.
scanSubscription.dispose();For devices with API <21 (before Lollipop) the scan API is emulated to get the same behaviour.
On Android it is not always trivial to determine if a particular BLE operation has a potential to succeed. e.g. to scan on Android 6.0 the device needs to have a BluetoothAdapter, the application needs to have a granted runtime permission for either ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION, additionally Location Services need to be turned on.
To be sure that the scan will work only when everything is ready you could use:
Disposable flowDisposable = rxBleClient.observeStateChanges()
.switchMap(state -> { // switchMap makes sure that if the state will change the rxBleClient.scanBleDevices() will dispose 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 dispose.
flowDisposable.dispose();For further BLE interactions the connection is required.
String macAddress = "AA:BB:CC:DD:EE:FF";
RxBleDevice device = rxBleClient.getBleDevice(macAddress);
Disposable disposable = device.establishConnection(false) // <-- autoConnect flag
.subscribe(
rxBleConnection -> {
// All GATT operations are done through the rxBleConnection.
},
throwable -> {
// Handle an error here.
}
);
// When done... dispose and forget about connection teardown :)
disposable.dispose();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. Unlike the native Android API, if autoConnect=true while using this library there will be NO attempts to automatically reconnect if the original connection is lost.
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.
device.establishConnection(false)
.flatMapSingle(rxBleConnection -> rxBleConnection.readCharacteristic(characteristicUUID))
.subscribe(
characteristicValue -> {
// Read characteristic value.
},
throwable -> {
// Handle an error here.
}
);device.establishConnection(false)
.flatMapSingle(rxBleConnection -> rxBleConnection.writeCharacteristic(characteristicUUID, bytesToWrite))
.subscribe(
characteristicValue -> {
// Characteristic value confirmed.
},
throwable -> {
// Handle an error here.
}
);device.establishConnection(false)
.flatMap(rxBleConnection -> Single.zip(
rxBleConnection.readCharacteristic(firstUUID),
rxBleConnection.readCharacteristic(secondUUID),
YourModelCombiningTwoValues::new
))
.subscribe(
model -> {
// Process your model.
},
throwable -> {
// Handle an error here.
}
);device.establishConnection(false)
.flatMap(rxBleConnection -> rxBleConnection.createNewLongWriteBuilder()
.setCharacteristicUuid(uuid) // required or the .setCharacteristic()
// .setCharacteristic() alternative if you have a specific BluetoothGattCharacteristic
.setBytes(byteArray)
// .setWriteOperationRetryStrategy(retryStrategy) // if you'd like to retry batch write operations on failure, provide your own retry strategy
// .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.
}
);device.establishConnection(false)
.flatMapSingle(rxBleConnection -> rxBleConnection.readCharacteristic(characteristicUuid)
.doOnSuccess(bytes -> {
// Process read data.
})
.flatMap(bytes -> rxBleConnection.writeCharacteristic(characteristicUuid, bytesToWrite))
)
.subscribe(
writeBytes -> {
// Written data.
},
throwable -> {
// Handle an error here.
}
);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.
}
);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.
}
);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));Every error you may encounter is provided via onError callback. Each public method has JavaDoc explaining possible errors.
From different interfaces, you can obtain different Observables which exhibit different behaviours.
There are two types of Observables that you may encounter.
- Multiple values - i.e.
RxBleClient.scan(),RxBleDevice.observeConnectionStateChanges()andObservableemitted byRxBleConnection.setupNotification()/RxBleConnection.setupIndication() - One value — these usually are meant for auto cleanup upon disposing i.e.
setupNotification()/setupIndication()— when you will dispose 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 dispose it which will cause disconnection and cleanup of resources.
The below table contains an overview of used Observable patterns
| Interface | Function | Number of values | Hot/Cold |
|---|---|---|---|
| RxBleClient | scanBleDevices()* | Infinite | cold |
| RxBleClient | observeStateChanges() | Infinite** | hot |
| RxBleDevice | observeConnectionStateChanges() | Infinite | hot |
| RxBleDevice | establishConnection()* | One | cold |
| RxBleConnection | setupNotification()* | One | cold |
| RxBleConnection | setupNotification() emitted Observable | Infinite** | hot |
| RxBleConnection | setupIndication()* | One | cold |
| RxBleConnection | setupIndication() emitted Observable | Infinite** | hot |
| RxBleConnection | queue() | User defined | cold |
* this Observable when disposed closes/cleans up internal resources (i.e. finishes scan, closes a connection, disables notifications)
** this Observable may complete. For example observeStateChanges() 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. A second example: Observables emitted from setupNotification / setupIndication may complete when the parent Observable is disposed.
We encourage you to check the package com.polidea.rxandroidble2.helpers and com.polidea.rxandroidble2.utils which contain handy reactive wrappers for some typical use-cases.
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.
If you would like to observe BluetoothAdapter state changes you can use RxBleAdapterStateObservable.
Usage examples are located in:
Keep in mind that these are only samples to show how the library can be used. These are not meant for being role model of a good application architecture.
Using RxAndroidBle enables you to test your application easily.
Most of the objects that the library uses are implementations of interfaces which can be mocked.
Alternatively one could use MockRxAndroidBle (more info below). Note: Using MockRxAndroidBle in unit tests needs Robolectric.
Sometimes there is a need to develop the application without the access to a physical device. We have created MockRxAndroidBle as a drop-in addon for mocking a simple peripheral.
Unfortunately it is not under active development—PRs are welcomed though. ;)
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.
If you encounter seemingly incorrect behaviour in your application that is regarding this library please check the below list of Frequently Asked Questions:
- non-commercial — head to StackOverflow #rxandroidble
- commercial — drop an email to hello@polidea.com for more info
Learn more about Polidea's BLE services here
Want to talk about it? Join our discussion on Gitter
- Dariusz Seweryn (github: dariuszseweryn)
Contributors, thank you!
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.
