A LiveData example when working with firebase database and LiveData, inspired by the examples of Android architecture guide lines

FirebaseItemLiveData.java

package com.devofure.tlog.repository.api;

import android.support.annotation.NonNull;

import com.devofure.tlog.model.Resource;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;

public abstract class FirebaseItemLiveData<RequestType>
         extends LiveDataRefresher<Resource<RequestType>> {

    private final DatabaseReference mRootDatabase;
    private ValueEventListener mEventItemListener;
    private Query mDbRef;
    private OnRefreshDbNodeListener mOnRefreshNode;

    public FirebaseItemLiveData(DatabaseReference rootDatabase) {
        mRootDatabase = rootDatabase;
    }

    @Override
    protected void onActive() {
        super.onActive();
        //save the last dbRef to remove listener later on onInactive
        mDbRef = getCurrentDbNodeRef(mRootDatabase);
        //save the last listener to remove listener later on onInactive
        mDbRef.addValueEventListener(mEventItemListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                setValue(Resource.success(convertTo(dataSnapshot)));
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                setValue(Resource.error(databaseError.getMessage(), null));
            }
        });
    }

    private Query getCurrentDbNodeRef(DatabaseReference rootDatabase) {
        if(mOnRefreshNode != null){
            return mOnRefreshNode.getDbNodeRef(rootDatabase);
        }else {
            return getDbNodeRef(rootDatabase);
        }
    }

    protected abstract Query getDbNodeRef(DatabaseReference rootDatabaseRef);

    @Override
    void refresh(@NonNull OnRefreshDbNodeListener onRefreshNode) {
        onInactive();
        onActive();
        mOnRefreshNode = onRefreshNode;
    }

    protected abstract RequestType convertTo(DataSnapshot dataSnapshot);


    @Override
    protected void onInactive() {
        super.onInactive();
        mDbRef.removeEventListener(mEventItemListener);
    }
}

LiveDataRefresher.java

package com.devofure.tlog.repository.api;

import android.arch.lifecycle.LiveData;
import android.support.annotation.NonNull;

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.Query;

public abstract class LiveDataRefresher<RequestType> extends LiveData<RequestType> {

    abstract void refresh(@NonNull OnRefreshDbNodeListener onRefreshNode);

    interface OnRefreshDbNodeListener {
        Query getDbNodeRef(DatabaseReference rootDatabase);
    }
}

Resource.java

package com.devofure.tlog.model;


import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import static com.devofure.tlog.model.Status.ERROR;
import static com.devofure.tlog.model.Status.LOADING;
import static com.devofure.tlog.model.Status.SUCCESS;

public class Resource<T> {

    @NonNull
    public final Status status;

    @Nullable
    public final String message;

    @Nullable
    public final T data;

    public Resource(@NonNull Status status, @Nullable T data, @Nullable String message) {
        this.status = status;
        this.data = data;
        this.message = message;
    }

    public static <T> Resource<T> success() {
        return success(null);
    }
    public static <T> Resource<T> success(@Nullable T data) {
        return new Resource<>(SUCCESS, data, null);
    }

    public static <T> Resource<T> error(String msg, @Nullable T data) {
        return new Resource<>(ERROR, data, msg);
    }

    public static <T> Resource<T> loading() {
        return loading(null);
    }
    public static <T> Resource<T> loading(@Nullable T data) {
        return new Resource<>(LOADING, data, null);
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        Resource<?> resource = (Resource<?>) o;

        if (status != resource.status) {
            return false;
        }
        if (message != null ? !message.equals(resource.message) : resource.message != null) {
            return false;
        }
        return data != null ? data.equals(resource.data) : resource.data == null;
    }

    @Override
    public int hashCode() {
        int result = status.hashCode();
        result = 31 * result + (message != null ? message.hashCode() : 0);
        result = 31 * result + (data != null ? data.hashCode() : 0);
        return result;
    }

    @Override
    public String toString() {
        return "Resource{" +
                "status=" + status +
                ", message='" + message + '\'' +
                ", data=" + data +
                '}';
    }
}