Is it possible to make one LiveData of two LiveDatas?

Question

I have two DAOs, two Repositories and two POJOs. There is some way to create one Livedata of two? I need it to make single list for Recyclerview. POJOs are similar objects.<

Answer 1

I assume you want to combine them, yes? You'll need a MediatorLiveData, but the guy saying you now need Object is wrong. What you need is a MediatorLiveData, List>>.

public class CombinedLiveData extends MediatorLiveData, List>> {
    private List expenses = Collections.emptyList();
    private List incomes = Collections.emptyList();

    public CombinedLiveData(LiveData> ld1, LiveData> ld2) {
        setValue(Pair.create(expenses, incomes));

        addSource(ld1, expenses -> { 
             if(expenses != null) {
                this.expenses = expenses;
             } 
             setValue(Pair.create(expenses, incomes)); 
        });

        addSource(ld2, incomes -> { 
            if(incomes != null) {
                this.incomes = incomes;
            } 
            setValue(Pair.create(expenses, incomes));
        });
    }
}

You could potentially make this generic and it'd be the implementation of combineLatest for two LiveData using tuples of 2-arity (Pair).

EDIT: like this:

public class CombinedLiveData2 extends MediatorLiveData> {
    private A a;
    private B b;

    public CombinedLiveData2(LiveData ld1, LiveData ld2) {
        setValue(Pair.create(a, b));

        addSource(ld1, a -> { 
             if(a != null) {
                this.a = a;
             } 
             setValue(Pair.create(a, b)); 
        });

        addSource(ld2, b -> { 
            if(b != null) {
                this.b = b;
            } 
            setValue(Pair.create(a, b));
        });
    }
}

Beware that I lost the ability to set Collections.emptyList() as initial values of A and B with this scenario, and you WILL need to check for nulls when you access the data inside the pair.

EDIT: You can use the library https://github.com/Zhuinden/livedata-combinetuple-kt which does the same thing.