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

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.rxandroidble3:rxandroidble:1.18.1"

or for RxJava 2 based artifact

implementation "com.polidea.rxandroidble2:rxandroidble:1.18.1"

If you use Maven to build your project — as a Maven project dependency:

<dependency>
  <groupId>com.polidea.rxandroidble3</groupId>
  <artifactId>rxandroidble</artifactId>
  <version>1.18.1</version>
  <type>aar</type>
</dependency>

or for RxJava 2 based artifact

<dependency>
  <groupId>com.polidea.rxandroidble2</groupId>
  <artifactId>rxandroidble</artifactId>
  <version>1.18.1</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 requires additional permissions declared in the manifest for an app to run a BLE scan since API 23 (6.0 / Marshmallow) and perform a BLE connection since API 31 (Android 12). RxAndroidBle provides a minimal set of commonly used bluetooth permissions for you in its AndroidManifest.xml. These permissions currently assume scanning is only used when the App is in the foreground, and that the App wants to derive the user's location from BLE signal (on API >= 23). Below are a number of additions you can make to your AndroidManifext.xml for your specific use case.

RxAndroidBle uses the uses-permission-sdk-23 tag to require location only on APIs >= 23, where it is required for BLE scanning. Additionally, in a future version of RxAndroidBle, these permissions will be restricted to only APIs 23-30. To ensure you can derive the user's location in your App with all API versions, and avoid any issues with merging of permissions when uploading to the Play Store, add the following to your AndroidManifest.xml:

<uses-permission-sdk-23 android:name="android.permission.ACCESS_FINE_LOCATION" tools:node="remove" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission-sdk-23 android:name="android.permission.ACCESS_COARSE_LOCATION" tools:node="remove" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

If you only want to scan for BLE peripherals and do not access location otherwise you can request only the required permissions by adding the following to your AndroidManifest.xml:

<uses-permission-sdk-23 android:name="android.permission.ACCESS_COARSE_LOCATION" android:maxSdkVersion="30" tools:node="replace" />
<uses-permission-sdk-23 android:name="android.permission.ACCESS_FINE_LOCATION" android:maxSdkVersion="30" tools:node="replace" />

You should add the following to your AndroidManifest.xml:

<uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" android:maxSdkVersion="30" />

If you want to access the user's location in the background on APIs > 30, remove the android:maxSdkVersion attribute.

API 31 (Android 12) introduced new Bluetooth permissions. RxAndroidBle uses the android:usesPermissionFlags="neverForLocation" attribute on the BLUETOOTH_SCAN permission, which indicates scanning will not be used to derive the user's location, so location permissions are not required. If you need to locate the user with BLE scanning, use this instead, but keep in mind that you will still need ACCESS_FINE_LOCATION:

<uses-permission android:name="android.permission.BLUETOOTH_SCAN" tools:node="replace" />

You can remove the BLUETOOTH_CONNECT permission that RxAndroidBle requests in APIs >= 31:

<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" tools:node="remove" />

A summary of available runtime permissions used for BLE scanning:

* Needed if scan is performed in background

** Only needed if you want to obtain user's location with BLE scanning (BLUETOOTH_SCAN is not using neverForLocation attribute in your App)

A summary of available runtime permissions used for BLE connections:

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.

1. Multiple values - i.e. RxBleClient.scan(), RxBleDevice.observeConnectionStateChanges() and Observable emitted by RxBleConnection.setupNotification() / RxBleConnection.setupIndication()
2. 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

* 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:

• /sample
• /sample-kotlin

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:

• Cannot connect / Status 133
• UndeliverableException

• non-commercial — head to StackOverflow #rxandroidble
• commercial — contact the maintainer

Want to talk about it? Join our discussion on Gitter

• Dariusz Seweryn (github: dariuszseweryn)

Copyright 2016 Polidea Sp. z o.o
Copyright 2021 Dariusz Seweryn 

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.