A utility class to combine 2 LiveData in one, which basically emits value only when both the live data emits some non-null value value

CombineLiveData.java

package com.magicpin.local.groceryorders;

import android.util.Pair;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MediatorLiveData;

public class CombineLiveData<A, B> {
	
	private A lastA = null;
	private B lastB = null;
	
	public LiveData<Pair<A, B>> zipLiveData(LiveData<A> a, LiveData<B> b) {
		MediatorLiveData<Pair<A, B>> mediatorLiveData = new MediatorLiveData<>();
		mediatorLiveData.addSource(a, a1 -> {
			lastA = a1;
			update(mediatorLiveData);
		});
		
		mediatorLiveData.addSource(b, a2 -> {
			lastB = a2;
			update(mediatorLiveData);
		});
		
		return mediatorLiveData;
	}
	
	private void update(MediatorLiveData<Pair<A, B>> mediatorLiveData) {
		A localLastA = lastA;
		B localLastB = lastB;
		if (localLastA != null && localLastB != null)
			mediatorLiveData.setValue(new Pair<>(localLastA, localLastB));
	}
}