added in version 1.0.0
belongs to Maven artifact android.arch.lifecycle:livedata:1.1.1

Summary: Ctors | Methods | Protected Methods | Inherited Methods

MediatorLiveData

The android.arch Architecture Components packages are no longer maintained. They have been superseded by the corresponding androidx.* packages. See androidx.lifecycle.MediatorLiveData instead.

public class MediatorLiveData
extends MutableLiveData<T>

java.lang.Object
↳	android.arch.lifecycle.LiveData<T>
	↳	android.arch.lifecycle.MutableLiveData<T>
		↳	android.arch.lifecycle.MediatorLiveData<T>

---

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()

Public methods
<S> void	addSource(LiveData<S> source, Observer<S> onChanged) Starts to listen the given source LiveData, onChanged observer will be called when source value was changed.
<S> void	removeSource(LiveData<S> toRemote) Stops to listen the given LiveData.

Protected methods
void	onActive() Called when the number of active observers change to 1 from 0.
void	onInactive() Called when the number of active observers change from 1 to 0.

Inherited methods
From class android.arch.lifecycle.MutableLiveData void postValue(T value) Posts a task to a main thread to set the given value. void setValue(T value) Sets the value.
From class android.arch.lifecycle.LiveData T getValue() Returns the current value. boolean hasActiveObservers() Returns true if this LiveData has active observers. boolean hasObservers() Returns true if this LiveData has observers. void observe(LifecycleOwner owner, Observer<T> observer) Adds the given observer to the observers list within the lifespan of the given owner. void observeForever(Observer<T> observer) Adds the given observer to the observers list. void onActive() Called when the number of active observers change to 1 from 0. void onInactive() Called when the number of active observers change from 1 to 0. void postValue(T value) Posts a task to a main thread to set the given value. void removeObserver(Observer<T> observer) Removes the given observer from the observers list. void removeObservers(LifecycleOwner owner) Removes all observers that are tied to the given LifecycleOwner. void setValue(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

MediatorLiveData ()

Public methods

addSource

added in version 1.0.0

void addSource (LiveData<S> source, 
                Observer<S> 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 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

void removeSource (LiveData<S> toRemote)

Stops to listen the given LiveData.

Parameters
toRemote	LiveData: LiveData to stop to listen

Protected methods

onActive

added in version 1.0.0

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

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 or RESUMED (like an Activity in the back stack).

You can check if there are observers via hasObservers().

• Annotations

  • OnLifecycleEvent

• Interfaces

  • DefaultLifecycleObserver
  • LifecycleObserver
  • LifecycleOwner
  • LifecycleRegistryOwner
  • Observer
  • ViewModelProvider.Factory
  • ViewModelStoreOwner

• Classes

  • AndroidViewModel
  • Lifecycle
  • LifecycleRegistry
  • LifecycleService
  • LiveData
  • LiveDataReactiveStreams
  • MediatorLiveData
  • MutableLiveData
  • ProcessLifecycleOwner
  • ServiceLifecycleDispatcher
  • Transformations
  • ViewModel
  • ViewModelProvider
  • ViewModelProvider.AndroidViewModelFactory
  • ViewModelProvider.NewInstanceFactory
  • ViewModelProviders
  • ViewModelProviders.DefaultFactory
  • ViewModelStore
  • ViewModelStores

• Enums

  • Lifecycle.Event
  • Lifecycle.State