DatabaseReference and FirebaseDatabase - cannot resolve symbol

Question

I'm currently working on an institute level chat messaging application on Android. I'm using Firebase as my Cloud Server. Currently, I'm facing a Cannot Resolve Symbol error on DatabaseReference and FirebaseDatabase at the following line in my MainActivity:

private DatabaseReference root = FirebaseDatabase.getInstance().getReference().getRoot(); 

I want to make chat rooms using Firebase. I know how to do this, as well as how to link Keys and Values of my Firebase Database. I also know how to update the Keys and Values from an Android Device through Firebase Cloud.

But I'm not able to resolve the Cannot resolve Symbol error. Following is the code of my MainActivity. I'm still in initial stages of making this app.

    package com.ranatalha.realtimechat;  import android.content.DialogInterface; import android.os.Bundle; import android.support.v7.app.AlertDialog; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.EditText; import android.widget.ListView;  import java.util.ArrayList;  public class MainActivity extends AppCompatActivity {      private Button buttonAddRoom;     private EditText editTextAddaChatRoom;     private ListView listViewChatRooms;      private ArrayAdapter<String> arrayAdapter;     private ArrayList<String> list_of_rooms = new ArrayList<>();      private String Entered_Username;       private DatabaseReference root = FirebaseDatabase.getInstance().getReference().getRoot();      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          buttonAddRoom = (Button) findViewById(R.id.buttonAddRoom);         editTextAddaChatRoom = (EditText) findViewById(R.id.editTextAddaChatRoom);         listViewChatRooms = (ListView) findViewById(R.id.listViewChatRooms);  //************Creation of an array list to store the list of active chat rooms************         arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, list_of_rooms);          listViewChatRooms.setAdapter(arrayAdapter); //*****************************************************************************************         request_user_name();          buttonAddRoom.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {              }         });     }     private void request_user_name(){          AlertDialog.Builder builder = new AlertDialog.Builder(this);         builder.setTitle("Enter Your Name:");          final EditText inputUsername = new EditText(this);         builder.setView(inputUsername);          builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {             @Override             public void onClick(DialogInterface dialogInterface, int i) {                 Entered_Username = inputUsername.getText().toString();              }         });          builder.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {             @Override             public void onClick(DialogInterface dialogInterface, int i) {                 dialogInterface.cancel();                 request_user_name();             }         });          builder.show();      } } 

Answer 1

Can you please double check if you have these dependencies into your build.gradle (Module:app) file?

implementation 'com.google.firebase:firebase-analytics:17.2.1'     implementation 'com.google.firebase:firebase-database:19.2.0' 

The error goes away after adding those.