# MediatorLiveData added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) belongs to Maven artifact android.arch.lifecycle:livedata:1.1.1 Summary:[Ctors](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#pubctors)\|[Methods](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#pubmethods)\|[Protected Methods](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#promethods)\|[Inherited Methods](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#inhmethods) # MediatorLiveData | The`android.arch`Architecture Components packages are no longer maintained. They have been superseded by the corresponding[androidx.\*](https://developer.android.com/jetpack/androidx/migrate)packages. See[androidx.lifecycle.MediatorLiveData](https://developer.android.com/reference/androidx/lifecycle/MediatorLiveData)instead. ` public class MediatorLiveData ` ` `` `` extends `[MutableLiveData](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData)` `` ` |---|---|---|----------------------------------------------| | java.lang.Object |||| | ↳ | [android.arch.lifecycle.LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData)\ ||| | | ↳ | [android.arch.lifecycle.MutableLiveData](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData)\ || | | | ↳ | android.arch.lifecycle.MediatorLiveData\ |
*** ** * ** *** [LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData)subclass which may observe other`LiveData`objects and react on`OnChanged`events from them. This class correctly propagates its active/inactive states down to source`LiveData`objects. Consider the following scenario: we have 2 instances of`LiveData`, let's name them`liveData1`and`liveData2`, and we want to merge their emissions in one object:`liveDataMerger`. Then,`liveData1`and`liveData2`will become sources for the`MediatorLiveData liveDataMerger`and every time`onChanged`callback is called for either of them, we set a new value in`liveDataMerger`. ``` LiveData liveData1 = ...; LiveData liveData2 = ...; MediatorLiveData liveDataMerger = new MediatorLiveData<>(); liveDataMerger.addSource(liveData1, value -> liveDataMerger.setValue(value)); liveDataMerger.addSource(liveData2, value -> liveDataMerger.setValue(value)); ``` Let's consider that we only want 10 values emitted by`liveData1`, to be merged in the`liveDataMerger`. Then, after 10 values, we can stop listening to`liveData1`and remove it as a source. ``` liveDataMerger.addSource(liveData1, new Observer() { private int count = 1; @Override public void onChanged(@Nullable Integer s) { count++; liveDataMerger.setValue(s); if (count > 10) { liveDataMerger.removeSource(liveData1); } } }); ```
## Summary | ### Public constructors || |--------------------------------------------------------------------------------------------------------------------------------|---| | ` `[MediatorLiveData](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#MediatorLiveData())`() ` | | ### Public methods || |-------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` void` | ` `[addSource](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#addSource(android.arch.lifecycle.LiveData, android.arch.lifecycle.Observer))`(`[LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData)` source, `[Observer](https://developer.android.com/reference/android/arch/lifecycle/Observer)` onChanged) ` Starts to listen the given`source`LiveData,`onChanged`observer will be called when`source`value was changed. | | ` void` | ` `[removeSource](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#removeSource(android.arch.lifecycle.LiveData))`(`[LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData)` toRemote) ` Stops to listen the given`LiveData`. | | ### Protected methods || |---------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` void` | ` `[onActive](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#onActive())`() ` Called when the number of active observers change to 1 from 0. | | ` void` | ` `[onInactive](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData#onInactive())`() ` Called when the number of active observers change from 1 to 0. | | ### Inherited methods | |-----------------------|---| | From class` `[android.arch.lifecycle.MutableLiveData](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData)` ` |---------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` void` | ` `[postValue](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData#postValue(T))`(T value) ` Posts a task to a main thread to set the given value. | | ` void` | ` `[setValue](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData#setValue(T))`(T value) ` Sets the value. | || | From class` `[android.arch.lifecycle.LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData)` ` |------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` T` | ` `[getValue](https://developer.android.com/reference/android/arch/lifecycle/LiveData#getValue())`() ` Returns the current value. | | ` boolean` | ` `[hasActiveObservers](https://developer.android.com/reference/android/arch/lifecycle/LiveData#hasActiveObservers())`() ` Returns true if this LiveData has active observers. | | ` boolean` | ` `[hasObservers](https://developer.android.com/reference/android/arch/lifecycle/LiveData#hasObservers())`() ` Returns true if this LiveData has observers. | | ` void` | ` `[observe](https://developer.android.com/reference/android/arch/lifecycle/LiveData#observe(android.arch.lifecycle.LifecycleOwner, android.arch.lifecycle.Observer))`(`[LifecycleOwner](https://developer.android.com/reference/android/arch/lifecycle/LifecycleOwner)` owner, `[Observer](https://developer.android.com/reference/android/arch/lifecycle/Observer)` observer) ` Adds the given observer to the observers list within the lifespan of the given owner. | | ` void` | ` `[observeForever](https://developer.android.com/reference/android/arch/lifecycle/LiveData#observeForever(android.arch.lifecycle.Observer))`(`[Observer](https://developer.android.com/reference/android/arch/lifecycle/Observer)` observer) ` Adds the given observer to the observers list. | | ` void` | ` `[onActive](https://developer.android.com/reference/android/arch/lifecycle/LiveData#onActive())`() ` Called when the number of active observers change to 1 from 0. | | ` void` | ` `[onInactive](https://developer.android.com/reference/android/arch/lifecycle/LiveData#onInactive())`() ` Called when the number of active observers change from 1 to 0. | | ` void` | ` `[postValue](https://developer.android.com/reference/android/arch/lifecycle/LiveData#postValue(T))`(T value) ` Posts a task to a main thread to set the given value. | | ` void` | ` `[removeObserver](https://developer.android.com/reference/android/arch/lifecycle/LiveData#removeObserver(android.arch.lifecycle.Observer))`(`[Observer](https://developer.android.com/reference/android/arch/lifecycle/Observer)` observer) ` Removes the given observer from the observers list. | | ` void` | ` `[removeObservers](https://developer.android.com/reference/android/arch/lifecycle/LiveData#removeObservers(android.arch.lifecycle.LifecycleOwner))`(`[LifecycleOwner](https://developer.android.com/reference/android/arch/lifecycle/LifecycleOwner)` owner) ` Removes all observers that are tied to the given[LifecycleOwner](https://developer.android.com/reference/android/arch/lifecycle/LifecycleOwner). | | ` void` | ` `[setValue](https://developer.android.com/reference/android/arch/lifecycle/LiveData#setValue(T))`(T value) ` Sets the value. | || | From class` java.lang.Object ` |-------------------|-------------------------------| | ` Object` | ` clone() ` | | ` boolean` | ` equals(Object arg0) ` | | ` void` | ` finalize() ` | | ` final Class` | ` getClass() ` | | ` int` | ` hashCode() ` | | ` final void` | ` notify() ` | | ` final void` | ` notifyAll() ` | | ` String` | ` toString() ` | | ` final void` | ` wait(long arg0, int arg1) ` | | ` final void` | ` wait(long arg0) ` | | ` final void` | ` wait() ` | || ## Public constructors ### MediatorLiveData added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) ``` MediatorLiveData () ```

## Public methods ### addSource added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) ``` void addSource (LiveData source, Observer onChanged) ``` Starts to listen the given`source`LiveData,`onChanged`observer will be called when`source`value was changed. `onChanged`callback will be called only when this`MediatorLiveData`is active. If the given LiveData is already added as a source but with a different Observer,[IllegalArgumentException](https://developer.android.com/reference/java/lang/IllegalArgumentException)will be thrown.
| Parameters || |-------------|--------------------------------------------------------------| | `source` | `LiveData`: the`LiveData`to listen to
| | `onChanged` | `Observer`: The observer that will receive the events
| ### removeSource added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) ``` void removeSource (LiveData toRemote) ``` Stops to listen the given`LiveData`.
| Parameters || |------------|-----------------------------------------------| | `toRemote` | `LiveData`:`LiveData`to stop to listen
| ## Protected methods ### onActive added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) ``` void onActive () ``` Called when the number of active observers change to 1 from 0. This callback can be used to know that this LiveData is being used thus should be kept up to date.
### onInactive added in[version 1.0.0](https://developer.android.com/topic/libraries/support-library/revisions) ``` void onInactive () ``` Called when the number of active observers change from 1 to 0. This does not mean that there are no observers left, there may still be observers but their lifecycle states aren't[STARTED](https://developer.android.com/reference/android/arch/lifecycle/Lifecycle.State#STARTED)or[RESUMED](https://developer.android.com/reference/android/arch/lifecycle/Lifecycle.State#RESUMED)(like an Activity in the back stack). You can check if there are observers via[hasObservers()](https://developer.android.com/reference/android/arch/lifecycle/LiveData#hasObservers()).
- ## Annotations - [OnLifecycleEvent](https://developer.android.com/reference/android/arch/lifecycle/OnLifecycleEvent) - ## Interfaces - [DefaultLifecycleObserver](https://developer.android.com/reference/android/arch/lifecycle/DefaultLifecycleObserver) - [LifecycleObserver](https://developer.android.com/reference/android/arch/lifecycle/LifecycleObserver) - [LifecycleOwner](https://developer.android.com/reference/android/arch/lifecycle/LifecycleOwner) - [LifecycleRegistryOwner](https://developer.android.com/reference/android/arch/lifecycle/LifecycleRegistryOwner) - [Observer](https://developer.android.com/reference/android/arch/lifecycle/Observer) - [ViewModelProvider.Factory](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProvider.Factory) - [ViewModelStoreOwner](https://developer.android.com/reference/android/arch/lifecycle/ViewModelStoreOwner) - ## Classes - [AndroidViewModel](https://developer.android.com/reference/android/arch/lifecycle/AndroidViewModel) - [Lifecycle](https://developer.android.com/reference/android/arch/lifecycle/Lifecycle) - [LifecycleRegistry](https://developer.android.com/reference/android/arch/lifecycle/LifecycleRegistry) - [LifecycleService](https://developer.android.com/reference/android/arch/lifecycle/LifecycleService) - [LiveData](https://developer.android.com/reference/android/arch/lifecycle/LiveData) - [LiveDataReactiveStreams](https://developer.android.com/reference/android/arch/lifecycle/LiveDataReactiveStreams) - [MediatorLiveData](https://developer.android.com/reference/android/arch/lifecycle/MediatorLiveData) - [MutableLiveData](https://developer.android.com/reference/android/arch/lifecycle/MutableLiveData) - [ProcessLifecycleOwner](https://developer.android.com/reference/android/arch/lifecycle/ProcessLifecycleOwner) - [ServiceLifecycleDispatcher](https://developer.android.com/reference/android/arch/lifecycle/ServiceLifecycleDispatcher) - [Transformations](https://developer.android.com/reference/android/arch/lifecycle/Transformations) - [ViewModel](https://developer.android.com/reference/android/arch/lifecycle/ViewModel) - [ViewModelProvider](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProvider) - [ViewModelProvider.AndroidViewModelFactory](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProvider.AndroidViewModelFactory) - [ViewModelProvider.NewInstanceFactory](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProvider.NewInstanceFactory) - [ViewModelProviders](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProviders) - [ViewModelProviders.DefaultFactory](https://developer.android.com/reference/android/arch/lifecycle/ViewModelProviders.DefaultFactory) - [ViewModelStore](https://developer.android.com/reference/android/arch/lifecycle/ViewModelStore) - [ViewModelStores](https://developer.android.com/reference/android/arch/lifecycle/ViewModelStores) - ## Enums - [Lifecycle.Event](https://developer.android.com/reference/android/arch/lifecycle/Lifecycle.Event) - [Lifecycle.State](https://developer.android.com/reference/android/arch/lifecycle/Lifecycle.State)