MainActivity.java

package com.example.ecom;

import android.app.ProgressDialog;

import android.content.Intent;

import android.os.Bundle;

import android.text.TextUtils;

import android.view.View;

import android.widget.Button;

import android.widget.Toast;

import androidx.annotation.NonNull;

import androidx.appcompat.app.AppCompatActivity;

import com.example.ecom.Model.Users;

import com.example.ecom.Prevalent.Prevalent;

import com.google.firebase.database.DataSnapshot;

import com.google.firebase.database.DatabaseError;

import com.google.firebase.database.DatabaseReference;

import com.google.firebase.database.FirebaseDatabase;

import com.google.firebase.database.ValueEventListener;

import io.paperdb.Paper;

public class MainActivity extends AppCompatActivity {

private Button joinNowButton, loginButton;

private ProgressDialog loadingBar;

private DataSnapshot dataSnapshot;

// private String parentDbName = "Users";

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    joinNowButton = (Button) findViewById(R.id.main_join_now_btn);

    loginButton = (Button) findViewById(R.id.main_login_btn);

    loadingBar = new ProgressDialog(this);

    Paper.init(this);

    loginButton.setOnClickListener(new View.OnClickListener() {

        @Override

        public void onClick(View view) {

            Intent intent = new Intent(MainActivity.this, LoginActivity1.class);

            startActivity(intent);
        }
    });

    joinNowButton.setOnClickListener(new View.OnClickListener() {

        @Override

        public void onClick(View view) {

            Intent intent = new Intent(MainActivity.this,RegisterActivity.class);

            startActivity(intent);
        }
    });

    String UserPhoneKey = Paper.book().read(Prevalent.UserPhoneKey);

    String UserPasswordKey = Paper.book().read(Prevalent.UserPasswordKey);

    if (UserPhoneKey!="" && UserPasswordKey!="")

    {

        if (!TextUtils.isEmpty(UserPhoneKey) && !TextUtils.isEmpty(UserPasswordKey))

        {

            AllowAccess(UserPhoneKey,UserPasswordKey);

            loadingBar.setTitle("Already Logged in");

            loadingBar.setMessage("Please wait...");

            loadingBar.setCanceledOnTouchOutside(false);

            loadingBar.show();

        }
    }
}

private void AllowAccess(final String phone, final String password) {



    final DatabaseReference RootRef;

    RootRef = FirebaseDatabase.getInstance().getReference();

    RootRef.addListenerForSingleValueEvent(new ValueEventListener() {

        @Override

        public void onDataChange(@NonNull DataSnapshot snapshot) {

            if (dataSnapshot.child("Users").child(phone).exists())

            {
                 Users usersData = dataSnapshot.child("Users").child(phone).getValue(Users.class);

                if (usersData.getPhone().equals(phone))

                {
                    if (usersData.getPassword().equals(password))

                    {
                        Toast.makeText(MainActivity.this, "please wait, logging in...", Toast.LENGTH_SHORT).show();
                        loadingBar.dismiss();

                        Intent intent = new Intent(MainActivity.this,HomeActivity.class);

                        Prevalent.currentOnlineUser = usersData;

                        startActivity(intent);
                    }
                    else
                    {
                        loadingBar.dismiss();

                        Toast.makeText(MainActivity.this, "Incorrect Password.", Toast.LENGTH_SHORT).show();
                    }
                }
            }
            else
            {
                Toast.makeText(MainActivity.this, "Account with this"   phone  "number do not exists", Toast.LENGTH_SHORT).show();

                loadingBar.dismiss();

            }
        }

        @Override

        public void onCancelled(@NonNull DatabaseError error) {

        }
    });

}

}

CodePudding user response：

Make sure you initialize the firebase app in your application class.

   @Override
    public void onCreate() {
    super.onCreate();
    FirebaseApp.initializeApp(this);
   }`