How to get data from firebase database, which has the structure of nested arrays and objects?

Question

I tried code to extract data from many places, but everywhere I get how to extract data to a simple list. Since the structure of my JSON is complex, and I can’t change it now, so please help me in getting data from the firebase database. Please help as I cannot understand the Firebase code . Below is the code for 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: I used to use an asset file, but now I want to get data from firebase, whose code is ambiguous on the Internet

 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 retrieve data from a Firebase database is with a ValueEventListener . Firebase works with asynchronous calls, so you cannot call a function, get data, and use it. You must install the ValueEventListener in a specific database link.

For your real problem, you need to create an array, set up a Firebase Reference, add a ValueEventListener, and inside add each occurrence of CategoryList to the array. Finally, still inside the ValueEventListener, you can create your CategoryModel with an array of CategoryList as a parameter and update your user interface to see the data in the 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 this to work, the CategoryList class must implement all the settings of its members, so "datasnapshot.getValue ()" works. Another approach could be to create a constructor in a CategoryList that recibe DataSnapshot like this:

 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 a constructor, you must replace this line:

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

with this:

 CategoryList categoryList = new CategoryList(childSnapshot); 

You can see that I am using the GenericTypeIndicator to work with data collections, this is a helper class that Firebase provides for working with Lists, maps, sets or another collection.

Answer 2

Just a recommendation! This is not a good data structure; you must denormalize your data. Then you can observe your data using ChildEventListener or ValueEventListener .

For example:

 -Category --CategoryId ---CategoryList ---Persons ----user1: true ----user2: true, etc. -Users --user1Id ---user1details --user2Id ---user2details, etc. 

Here are some useful links about denormalizing your data.

Link1 , Link2