How to retrieve data from firebase database which is having nested array and objects structure?

Question

I tried data extraction code from many places but everywhere i get how to retrieve data in a simple list. As the structure of my JSON is complex and i can't change it now, so please help me in retrieving data from firebase database. Please help as i am not able to understand Firebase code. Following is my code and JSON database:

CategoryModel.xml

package com.example.firedb;

import android.os.Parcel;
import android.os.Parcelable;

import java.util.ArrayList;

/**
 * Created by Android on 5/31/2017.
 */

public class CategoryModel {

    private ArrayList<CategoryList> categoryList;

    public CategoryModel() {
    }

    public CategoryModel(ArrayList<CategoryList> categoryList) {
        this.categoryList = categoryList;
    }

    public ArrayList<CategoryList> getCategoryList() {
        return categoryList;
    }

    public void setCategoryList(ArrayList<CategoryList> categoryList) {
        this.categoryList = categoryList;
    }


    // CategoryList

    public  static class CategoryList {

        public int Category_id;
        public String Category_name;
        public ArrayList<String>Emails;
        public ArrayList<String>Epabx;
        public ArrayList<String>Category_Fax;
        public ArrayList<Persons> persons;

        public CategoryList() {
        }
        //constructor of CategoryList

        public CategoryList(int category_id, String category_name,
                            ArrayList<String> emails, ArrayList<String> epabx, ArrayList<String> category_Fax,
                            ArrayList<Persons> persons) {
            Category_id = category_id;
            Category_name = category_name;
            Emails = emails;
            Epabx = epabx;
            Category_Fax = category_Fax;
            this.persons = persons;
        }

        // getters and setters of CategoryList

        public int getCategory_id() {
            return Category_id;
        }

        public void setCategory_id(int category_id) {
            Category_id = category_id;
        }

        public String getCategory_name() {
            return Category_name;
        }

        public void setCategory_name(String category_name) {
            Category_name = category_name;
        }

        public ArrayList<String> getEmails() {
            return Emails;
        }

        public void setEmails(ArrayList<String> emails) {
            Emails = emails;
        }

        public ArrayList<String> getEpabx() {
            return Epabx;
        }

        public void setEpabx(ArrayList<String> epabx) {
            Epabx = epabx;
        }

        public ArrayList<String> getCategory_Fax() {
            return Category_Fax;
        }

        public void setCategory_Fax(ArrayList<String> category_Fax) {
            Category_Fax = category_Fax;
        }

        public ArrayList<Persons> getPersons() {
            return persons;
        }

        public void setPersons(ArrayList<Persons> persons) {
            this.persons = persons;
        }


    }

    //Persons

    public static class Persons {

        private int Person_ID;
        private String Name;
        private String Designation;
        private ArrayList<String> Office_Phone;
        private ArrayList<String> Residence_Phone;
        private String VOIP;
        private String Address;
        private ArrayList<String>Fax;
        private String Ext;
        private ArrayList<String>Extra_info;
        private String Category_name;

        public Persons() {
        }

        // Constructor of Persons
        public Persons(int person_ID, String name, String designation, ArrayList<String> office_Phone,
                       ArrayList<String> residence_Phone, String VOIP, String address, ArrayList<String> fax, String ext,
                       ArrayList<String>extra_info, String category_name) {
            Person_ID = person_ID;
            Name = name;
            Designation = designation;
            Office_Phone = office_Phone;
            Residence_Phone = residence_Phone;
            this.VOIP = VOIP;
            Address = address;
            Fax = fax;
            Ext = ext;
            Extra_info=extra_info;
            Category_name=category_name;
        }

        // Getter and Setters of Persons

        public int getPerson_ID() {
            return Person_ID;
        }

        public void setPerson_ID(int person_ID) {
            Person_ID = person_ID;
        }

        public String getName() {
            return Name;
        }

        public void setName(String name) {
            Name = name;
        }

        public String getDesignation() {
            return Designation;
        }

        public void setDesignation(String designation) {
            Designation = designation;
        }

        public ArrayList<String> getOffice_Phone() {
            return Office_Phone;
        }

        public void setOffice_Phone(ArrayList<String> office_Phone) {
            Office_Phone = office_Phone;
        }

        public ArrayList<String> getResidence_Phone() {
            return Residence_Phone;
        }

        public void setResidence_Phone(ArrayList<String> residence_Phone) {
            Residence_Phone = residence_Phone;
        }

        public String getVOIP() {
            return VOIP;
        }

        public void setVOIP(String VOIP) {
            this.VOIP = VOIP;
        }

        public String getAddress() {
            return Address;
        }

        public void setAddress(String address) {
            Address = address;
        }

        public ArrayList<String> getFax() {
            return Fax;
        }

        public void setFax(ArrayList<String> fax) {
            Fax = fax;
        }

        public String getExt() {
            return Ext;
        }

        public void setExt(String ext) {
            Ext = ext;
        }

        public ArrayList<String> getExtra_info() {
            return Extra_info;
        }

        public void setExtra_info(ArrayList<String> extra_info) {
            Extra_info = extra_info;
        }

        public String getCategory_name() {
            return Category_name;
        }

        public void setCategory_name(String category_name) {
            Category_name = category_name;
        }

    }

}

CardviewActivity: Earlier i used an asset file but now i want to get data from firebase whose code is ambiguous online

package com.example.firedb;

import android.content.Intent;
import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.text.Editable;
import android.text.LoginFilter;
import android.text.TextWatcher;
import android.util.Log;
import android.view.Gravity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;

import static android.R.attr.button;


public class CardViewActivity extends AppCompatActivity {
    Toolbar mActionBarToolbar;
    private RecyclerView mainRecyclerView;
    private RecyclerView.Adapter mainAdapter;
    private RecyclerView.LayoutManager mainLayoutManager;
    private static String LOG_TAG = "CardViewActivity";
    EditText inputSearchMain;
    private ArrayList<CategoryModel.CategoryList> categoryLists;
    TextView toolbar_title_main;
    ImageView back_cardviewActivity;
//    DatabaseHandler db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_card_view);

//         db = new DatabaseHandler (CardViewActivity.this);

        mActionBarToolbar = (Toolbar) findViewById(R.id.tool_bar);
        toolbar_title_main=(TextView)findViewById(R.id.toolbar_title);


//        mActionBarToolbar.setTitle("Hry. Govt. Telephone Directory");
       // mActionBarToolbar.setLogo(R.drawable.logotoolbar);

//        mActionBarToolbar.setTitleMargin(5,2,2,2);
        setSupportActionBar(mActionBarToolbar);
        getSupportActionBar().setDisplayShowTitleEnabled(false);
        toolbar_title_main.setText("Hry. Govt. Telephone Directory");
        back_cardviewActivity=(ImageView)findViewById(R.id.back);
        back_cardviewActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onBackPressed();
            }
        });

        categoryLists=new ArrayList<CategoryModel.CategoryList>();
        categoryLists.addAll(getmcategoryset());
        mainRecyclerView=(RecyclerView)findViewById(R.id.recyclerView_Main);
        mainRecyclerView.setHasFixedSize(true);
        mainLayoutManager=new LinearLayoutManager(this);
        mainRecyclerView.setLayoutManager(mainLayoutManager);
//        Log.d( "onCreate: ", "List Size: "+categoryLists.size());
        mainAdapter=new RecyclerViewAdapterMain(getmcategoryset());
        mainRecyclerView.setAdapter(mainAdapter);
        inputSearchMain = (EditText) findViewById(R.id.inputSearchMain);

        addTextListener();
    }

    public void addTextListener(){

        inputSearchMain.addTextChangedListener(new TextWatcher() {

            public void afterTextChanged(Editable s) {}

            public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

            public void onTextChanged(CharSequence query, int start, int before, int count) {

                query = query.toString().toLowerCase();

                final ArrayList<CategoryModel.CategoryList> filteredList = new ArrayList<CategoryModel.CategoryList>();

                for (int i = 0; i < categoryLists.size(); i++) {

                    final String text = categoryLists.get(i).getCategory_name().toLowerCase();
                    if (text.contains(query)) {

                        filteredList.add(categoryLists.get(i));
                    }
                }

                mainRecyclerView.setLayoutManager(new LinearLayoutManager(CardViewActivity.this));
                mainAdapter = new RecyclerViewAdapterMain(filteredList);
                mainRecyclerView.setAdapter(mainAdapter);
                mainAdapter.notifyDataSetChanged();  // data set changed
            }
        });
    }

    private ArrayList<CategoryModel.CategoryList> getmcategoryset() {
//        JSONObject obj = new JSONObject(readJSONFromAsset());

        try {

            ArrayList<CategoryModel.CategoryList>categoryList = new ArrayList<CategoryModel.CategoryList>();
            JSONObject jsonObject = new JSONObject(readJSONFromAsset());

            JSONArray categoryArray = jsonObject.getJSONArray("Category");
            Log.d("getmcategoryset", "category count: "+categoryArray.length());
            for (int i = 0; i < categoryArray.length(); i++)
            {
                JSONObject job = categoryArray.getJSONObject(i);

                int categoryId = job.getInt("Category_id");
                String categoryName = job.getString("Category_name");

                //this is for email array
                ArrayList<String> emails = new ArrayList<>();
                JSONArray emailArray = job.getJSONArray("Emails");
                for (int j = 0; j< emailArray.length(); j++){
//                    JSONObject jobE = emailArray.getString(j);
                    emails.add(emailArray.getString(j));
                }

                //This i for Epabx array
                ArrayList<String> epabx = new ArrayList<>();
                JSONArray epabxArray = job.getJSONArray("Epabx");
                for (int j = 0; j < epabxArray.length(); j++){
//                    JSONObject jobE = epabxArray.getString(j);
                    epabx.add(epabxArray.getString(j));
                }

                //This i for Category_Fax array
                ArrayList<String> category_Fax = new ArrayList<>();
                JSONArray category_FaxJson = job.getJSONArray("Category_Fax");
                for (int j = 0; j < category_FaxJson.length(); j++){
//                    JSONObject jobE = category_FaxJson.getString(j);
                    category_Fax.add(category_FaxJson.getString(j));
                }

                //This i for Persons array
                ArrayList<CategoryModel.Persons> personsList = new ArrayList<>();
                JSONArray personsArray = job.getJSONArray("Persons");
                for (int j = 0; j < personsArray.length(); j++){
                    JSONObject jobIn = personsArray.getJSONObject(j);

                    int Person_ID = jobIn.getInt("Person_ID");
                    String Name = jobIn.getString("Name");
                    String Designation = jobIn.getString("Designation");

                    //this is for Office_Phone array
                    ArrayList<String>Office_Phone = new ArrayList<>();
                    JSONArray office_Phone = jobIn.getJSONArray("Office_Phone");
                    for (int k=0; k < office_Phone.length(); k++)
                    {
                        Office_Phone.add(office_Phone.getString(k));
                    }

                    //this is for Residence_Phone array
                    ArrayList<String>Residence_Phone = new ArrayList<>();
                    JSONArray residence_Phone = jobIn.getJSONArray("Residence_Phone");
                    for (int k=0; k < residence_Phone.length(); k++)
                    {
                        Residence_Phone.add(residence_Phone.getString(k));
                    }

                    String VOIP = jobIn.getString("VOIP");
                    String Address = jobIn.getString("Address");


                    //this is for Fax array
                    ArrayList<String>Fax = new ArrayList<>();
                    JSONArray fax = jobIn.getJSONArray("Fax");
                    for (int k=0; k < fax.length(); k++)
                    {
                        Fax.add(fax.getString(k));
                    }

                    String Ext = jobIn.getString("Ext");

                    //this is for Extra_info array
                    ArrayList<String>Extra_info = new ArrayList<>();
                    JSONArray extra_info = jobIn.getJSONArray("Extra_info");
                    for (int k=0; k < extra_info.length(); k++)
                    {
                        Extra_info.add(extra_info.getString(k));
                    }

                    personsList.add(new CategoryModel.Persons(Person_ID, Name, Designation, Office_Phone, Residence_Phone,
                            VOIP, Address, Fax, Ext,Extra_info,categoryName));
//                    db.addPerson(new CategoryModel.Persons(Person_ID, Name, Designation, Office_Phone, Residence_Phone,
//                            VOIP, Address, Fax, Ext,Extra_info));
                }

                //here your Category[] value store in categoryArrayList
                categoryList.add(new CategoryModel.CategoryList(categoryId, categoryName, emails, epabx, category_Fax, personsList));

//                db.addCategory(new CategoryModel.CategoryList(categoryId, categoryName, emails, epabx, category_Fax, personsList));

                Log.i("categoryList size = ", ""+categoryArray.length());
                Log.i("cat_name=",""+categoryName);
            }

            if (categoryList != null)
            {
                Log.i("categoryList size = ", ""+categoryArray.length());
            }
            return categoryList;
        } catch (JSONException e) {
            e.printStackTrace();
            return null;
        }

    }

    @Override
    protected void onResume() {
        super.onResume();
//        ((RecyclerViewAdapterMain) mainAdapter).setOnItemClickListener(new RecyclerViewAdapterMain()
//                .CategoryClickListener() {
//            public void onItemClick(int position, View v) {
//                Log.i(LOG_TAG, " Clicked on Item " + position);
//            }
//        });
    }


}

RecyclerViewAdapter:

package com.example.firedb;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;


public class RecyclerViewAdapterMain extends RecyclerView.Adapter<RecyclerViewAdapterMain.CategoryObjectHolder> {
    private static String LOG_TAG = "categoryRecyclrVwAdptr";
    private  ArrayList<CategoryModel.CategoryList> mcategoryset;
    private static CategoryClickListener categoryClickListener;

    public static class CategoryObjectHolder extends RecyclerView.ViewHolder  {
        TextView category_name;
        /*TextView category_emails;
        TextView category_epabx;
        TextView category_fax;*/

        public CategoryObjectHolder(View itemView){
            super(itemView);
            category_name=(TextView)itemView.findViewById(R.id.category_name);
            /*category_emails=(TextView)itemView.findViewById(R.id.category_emails);
            category_epabx=(TextView)itemView.findViewById(R.id.category_epabx);
            category_fax=(TextView)itemView.findViewById(R.id.category_fax);*/
            Log.i(LOG_TAG, "Adding Listener");

        }
//        @Override
//        public void onClick(View v) {
//            categoryClickListener.onItemClick(getAdapterPosition(), v);
//        }
    }
//    public void setOnItemClickListener(CategoryClickListener categoryClickListener) {
//        this.categoryClickListener = categoryClickListener;
//    }

    public RecyclerViewAdapterMain(ArrayList<CategoryModel.CategoryList> myDataset) {
        mcategoryset = myDataset;
    }

    public CategoryObjectHolder onCreateViewHolder(ViewGroup parent,int viewType){
        View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.card_view_row_main_activity,parent,false);
        CategoryObjectHolder categoryObjectHolder=new CategoryObjectHolder(view);
        return categoryObjectHolder;
    }

    @Override
    public void onBindViewHolder(CategoryObjectHolder holder, final int position) {
        /*final StringBuilder stringBuilder_emails = new StringBuilder();
        for (String email : mcategoryset.get(position).getEmails()) {
            if (!stringBuilder_emails.toString().isEmpty()) {
                stringBuilder_emails.append(", ");
            }
            stringBuilder_emails.append(email);
        }

        final StringBuilder stringBuilder_Epabx = new StringBuilder();
        for (String epabx : mcategoryset.get(position).getEpabx()) {
            if (!stringBuilder_Epabx.toString().isEmpty()) {
                stringBuilder_Epabx.append(", ");
            }
            stringBuilder_Epabx.append(epabx);
        }

        final StringBuilder stringBuilder_Category_Fax = new StringBuilder();
        for (String category_Fax : mcategoryset.get(position).getCategory_Fax()) {
            if (!stringBuilder_Category_Fax.toString().isEmpty()) {
                stringBuilder_Category_Fax.append(", ");
            }
            stringBuilder_Category_Fax.append(category_Fax);
        }*/

        holder.category_name.setText(mcategoryset.get(position).getCategory_name());
        /*holder.category_emails.setText(stringBuilder_emails.toString());
        holder.category_epabx.setText(stringBuilder_Epabx.toString());
        holder.category_fax.setText(stringBuilder_Category_Fax.toString());*/
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent i = new Intent (v.getContext(), PeopleListActivity.class);
                i.putParcelableArrayListExtra("Persons",mcategoryset.get(position).getPersons());
                i.putStringArrayListExtra("emails",mcategoryset.get(position).getEmails());
                //i.putExtras(b);
                v.getContext().startActivity(i);

            }
        });
    }
    public void addItem(CategoryModel.CategoryList dataObj, int index) {
        mcategoryset.add(index, dataObj);
        notifyItemInserted(index);
    }

    public void deleteItem(int index) {
        mcategoryset.remove(index);
        notifyItemRemoved(index);
    }

    @Override
    public int getItemCount() {
        return mcategoryset.size();
    }

    public interface CategoryClickListener {
        public void onItemClick(int position, View v);
    }
}

Answer 1

The only way to get data from Firebase Database it's using a ValueEventListener. Firebase work with asynchronous calls, so you can't call the function, get the data and use it. You have to set a ValueEventListener in a specific database reference.

For your actual problem, you have to create an array, set the Firebase Reference, add the ValueEventListener and inside add each occurrence of CategoryList in the array. Finally , still inside of the ValueEventListener, you can create your CategoryModel, with the CategoryList's array as parameter, and update your UI, to see the data in CategoryModel:

CategoryModel categoryModel;
ArrayList<CategoryList> array = new ArrayList<>();
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference categoryRef = database.getReference("Category");
categoryRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // This method is called once with the initial value and again
        // whenever data at this location is updated.
        for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
            CategoryList categoryList = childSnapshot.getValue(CategoryList.class);
            array.add(categoryList);
        }
        categoryModel = new CategoryModel(array);
        // Method to show the data in category model, 
        // usually populating an ListView or something
        updateUI()
    }

    @Override
    public void onCancelled(DatabaseError error) {
        // Failed to read value
        Log.w(TAG, "Failed to read value.", error.toException());
    }
});

For have this working, your CategoryList class has to implement all the setters of his members so "datasnapshot.getValue()" works. Another approach can be, create a Constructor in CategoryList that recibe a DataSnapshot in this way:

public CategoryList(DataSnapshot snapshot){
    Category_id = snapshot.child("Category_id").getValue(int.class);
    Category_name = snapshot.child("Category_name").getValue(String.class);
    GenericTypeIndicator<List<String>> stringList = new GenericTypeIndicator<List<String>>() {};
    Emails = snapshot.child("Emails").getValue(stringList);
    Epabx= snapshot.child("Epabx").getValue(stringList);
    Category_Fax= snapshot.child("Category_Fax").getValue(stringList);
    GenericTypeIndicator<List<Persons>> personsList = new GenericTypeIndicator<List<Persons>>() {};
    persons = snapshot.child("Persons").getValue(personsList);
}

If you create the constructor, you have to replace this line:

CategoryList categoryList = childSnapshot.getValue(CategoryList.class);

with this:

CategoryList categoryList = new CategoryList(childSnapshot);

You can see that I use GenericTypeIndicator to work with collections of data, this is a helper class provide for Firebase to work with Lists, Maps, Sets or another Collection.

Answer 2

Just a recommendation! This is not a good data structure, you should denormalize your data.Then you can observe your data by ChildEventListener or ValueEventListener.

For example:

-Category
--CategoryId
---CategoryList
---Persons
----user1: true
----user2: true, etc.

-Users
--user1Id
---user1details
--user2Id
---user2details, etc.

Here is some useful links about denormalizing your data

Link1, Link2