androidx.lifecycle.MediatorLiveData Maven / Gradle / Ivy
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/*
* Copyright (C) 2017 The Android Open Source Project
*
* 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.
*/
package androidx.lifecycle;
import android.arch.core.internal.SafeIterableMap;
import android.support.annotation.CallSuper;
import android.support.annotation.MainThread;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import java.util.Map;
/**
* {@link LiveData} subclass which may observe other {@code LiveData} objects and react on
* {@code OnChanged} events from them.
*
* This class correctly propagates its active/inactive states down to source {@code LiveData}
* objects.
*
* Consider the following scenario: we have 2 instances of {@code LiveData}, let's name them
* {@code liveData1} and {@code liveData2}, and we want to merge their emissions in one object:
* {@code liveDataMerger}. Then, {@code liveData1} and {@code liveData2} will become sources for
* the {@code MediatorLiveData liveDataMerger} and every time {@code onChanged} callback
* is called for either of them, we set a new value in {@code liveDataMerger}.
*
*
* LiveData<Integer> liveData1 = ...;
* LiveData<Integer> liveData2 = ...;
*
* MediatorLiveData<Integer> 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 {@code liveData1}, to be
* merged in the {@code liveDataMerger}. Then, after 10 values, we can stop listening to {@code
* liveData1} and remove it as a source.
*
* liveDataMerger.addSource(liveData1, new Observer<Integer>() {
* private int count = 1;
*
* {@literal @}Override public void onChanged(@Nullable Integer s) {
* count++;
* liveDataMerger.setValue(s);
* if (count > 10) {
* liveDataMerger.removeSource(liveData1);
* }
* }
* });
*
*
* @param The type of data hold by this instance
*/
public class MediatorLiveData extends android.arch.lifecycle.MediatorLiveData {
}