Introduction: convert LiveData to RxJava
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LiveDataToRxJava is a language extension library that provides some API for converting LiveData to RxJava.



Convert to Reactive interface

With the kotlin extension function, you can easily convert LiveData to RxJava:

val completable = liveData.toCompletable()
val observable = liveData.toObservable()
val flowable = liveData.toFlowable()
val single = liveData.toSingle()
val maybe = liveData.toMaybe()

If you are using Java, Api will be slightly longer:

MutableLiveData<String> liveData = new MutableLiveData<>();

Completable completable = RxJavaConvert.toCompletable(liveData);
Observable<String> observable = RxJavaConvert.toObservable(liveData);
Flowable<String> flowable = RxJavaConvert.toFlowable(liveData);
Single<String> single = RxJavaConvert.toSingle(liveData);
Maybe<String> maybe = RxJavaConvert.toMaybe(liveData);


LiveData can specify the period of observation in the lifecycle of a LifecycleOwner. In our applications including Android support-26 library, the commonly used Activity and Fragment has implemented the LifecycleOwner interface, so it can be very convenient to use our data in the lifecycle of UI.

The following code can be used to convert LifecycleOwner into a Observable:

//`this` can be an Activity or a Fragment
val observable: Observable<Lifecycle.Event> = LifecycleConvert.lifecycleObservable(this)

More often, you can obtain a observable with lifecycle:

//`this` can be an Activity or a Fragment
val observableWithLife = observable.bindLifecycle(this)
val singleWithLife = single.bindLifecycle(this)
val maybeWithLife = maybe.bindLifecycle(this)
val flowableWithLife = flowable.bindLifecycle(this)
val completableWithLife = completable.bindLifecycle(this)

The bindLifecycle operator allows your observable to have the same lifecycle as LiveData.observe (this, {doSomething}) , that is, from onStart state to onPause state.

Binding Lifecycle Operators Not only Applies to Observable (or other Reactive interfaces) converted from LiveData. So you can also use this library for other RxJava behavior binding lifecycle, such as Retrofit network requests, which automatically dispose those requests when ui is no longer active.

Other details

Null value

There is a difference between LiveData and Reactive interface. LiveData can pass null value, but the Reactive interface can't. So the null value is awkward while converting to RxJava. The toObservable operator throws an exception when it encounters a null value. Here are a few of my suggestions for this:

  1. Define a constant or object that represents null, and use it instead.
  2. Use Java8 Optional to wrap a nullable object.
  3. Use toObservableAllowNull APIs
val observable = liveData.toObservableAllowNull(valueIfNull)
val single = liveData.toSingleAllowNull(valueIfNull)
val maybe = liveData.toMaybeAllowNull(valueIfNull)
val flowable = liveData.toFlowableAllowNull(valueIfNull)
val completable = liveData.toCompletableAllowNull()

Non thread safe

LiveData is non-thread-safe. The main methods, such as observe, observeForever, removeObserver, setValue, all need to be called on the main thread. This means that it is still necessary to subscribe in the main thread after the conversion into the Observable (or other reactive interface). This is regrettable but temporarily unavoidable.

Values emitted out of the lifecycle

These values will be ignored when Flowable or Observable emitts values outside the lifecycle. But for Single, the only poor value, if ignored, is Maybe :

val maybe = single.bindLifecycle(this)

And if you still want to operate on Single, you can do this:

val singleWithLife = single.bindLifecycleWithError(this)

A CancellationException will be thrown when values are emitted outside the lifecycle. Completable is the same.


Add it in your root build.gradle at the end of repositories:

allprojects {
    repositories {
        maven { url '' }

Add the dependency:

dependencies {
    compile 'com.github.YvesCheung:LiveDataToRxJava:v1.1'


   Copyright 2018 Yves Cheung

   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

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   See the License for the specific language governing permissions and
   limitations under the License.
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