FA GOOGLE LoginWithPhoneAuth-MainActivity.java

package com.arslan6015.firebaseauthusingphoneno;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity {
        private EditText editTextMobile;
        Button btnContinue;
        FirebaseUser currentUser;

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

            //initialize fields
            editTextMobile = findViewById(R.id.editTextMobile);
            btnContinue = findViewById(R.id.buttonContinue);
            currentUser = FirebaseAuth.getInstance().getCurrentUser();

            //check whether the user is logged in 
            if (currentUser != null) {
                Intent intent = new Intent(MainActivity.this, ProfileActivity.class);
                startActivity(intent);
                finish();
            } else {
                btnContinue.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {

                        String mobileNo = editTextMobile.getText().toString().trim();

                        if (mobileNo.isEmpty() || mobileNo.length() < 12) {
                            editTextMobile.setError("Enter a valid mobile");
                            editTextMobile.requestFocus();
                            return;
                        }

                        Intent intent = new Intent(MainActivity.this, VerifyPhoneActivity.class);
                        intent.putExtra("mobile", mobileNo);
                        startActivity(intent);
                    }
                });
            }
        }
}