NAuth | Authentication process encapsulation component written by Qt

All You Have to do is First Use Auth for Login then Send Current user Id to Your Firebase Database and check if user exists or not.!
Here is sample code hope this might help you.!



      //get User Entered Values from EditText Fields.!
    String email=emailEditText.getText().toString().trim();
    String password=passwordEditText.getText().toString().trim();

     /logging in the user
mAuth.signInWithEmailAndPassword(email, password)
.addOnCompleteListener(this, new OnCompleteListener() {
 @Override
 public void onComplete(@NonNull Task task) {

  //if the task is successfull
  if(task.isSuccessful()){

  AddEventFireBaseListner(mAuth.getCurrentUser().getUid(),email, password);

  }






private void AddEventFireBaseListner(String uid,String email,String password){

  final User user;
             mdatabaseReference.child("users").orderByKey().equalTo(uid).addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
 public void onDataChange(DataSnapshot dataSnapshot) {

for (DataSnapshot postsnapshot : dataSnapshot.getChildren()) {

  user= postsnapshot.getValue(User.class);



 }//end of comments


    if(user!=null){

 if (user.getemail().equalsIgnoreCase(email) && user.getpassword().equalsIgnoreCase(password)) {

 Intent intent = new Intent(getApplicationContext(), MainActivity.class);

    //Parcalable object 
  intent.putExtra("userObj",user);

  startActivity(intent);


  }



  }
}
  else{
 Snackbar snackbar = Snackbar.make(coordinatorLayout, "Invalid user", Snackbar.LENGTH_LONG).setAction("HIDE", new View.OnClickListener() {
  @Override
   public void onClick(View view) {

    }
  });
   snackbar.show();
  }



  }

  @Override
  public void onCancelled(DatabaseError databaseError) {

   });//End 
    }

and for sending whole `user` object to next activity try to use `Parcelable` 





        public class User implements Parcelable {


        String name;

        String email;

        public User(String name, String email) {
            this.name = name;
            this.email = email;
        }


        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getEmail() {
            return email;
        }

        public void setEmail(String email) {
            this.email = email;
        }


        protected User(Parcel in) {
            name = in.readString();
            email = in.readString();
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            dest.writeString(name);
            dest.writeString(email);
        }

        @Override
        public int describeContents() {
            return 0;
        }

        public static final Creator CREATOR = new Creator() {
            @Override
            public User createFromParcel(Parcel in) {
                return new User(in);
            }

            @Override
            public User[] newArray(int size) {
                return new User[size];
            }
        };


        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", email='" + email + '\'' +
                    '}';
        }


    }