public class BlogSingleActivity extends AppCompatActivity {

private Button mSubmitBook;;
private DatabaseReference mDatabaseBookUser;
private FirebaseAuth firebaseAuth;


List<Blog> Info;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_blog_single);
    firebaseAuth= FirebaseAuth.getInstance();

    mSubmitBook = (Button) findViewById(R.id.SubmitBook);
    mDatabaseBookUser = FirebaseDatabase.getInstance().getReference("Users");

    Info = new ArrayList<>();

    mSubmitBook.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(view== mSubmitBook){
            addName();
            }
        }
    });
}

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

private Button buttonRegister;
private EditText mMatricField;
private EditText mNameField;
private EditText editTextEmail;
private EditText editTextPassword;
private TextView textViewSignin;

private ProgressDialog progressDialog;

private FirebaseAuth firebaseAuth;
private DatabaseReference mDatabase;

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

    firebaseAuth= FirebaseAuth.getInstance();


    if(firebaseAuth.getCurrentUser() !=null){
        //profile activity here
        finish();
        startActivity(new Intent(getApplicationContext(),ProfileActivity.class));
    }
    mDatabase= FirebaseDatabase.getInstance().getReference().child("Users");

    progressDialog=new ProgressDialog(this);

    buttonRegister=(Button) findViewById(R.id.buttonRegister);

    mMatricField= (EditText) findViewById(R.id.matricField);
    mNameField=(EditText) findViewById(R.id.nameField);
    editTextEmail=(EditText) findViewById(R.id.editTextEmail);
    editTextPassword=(EditText) findViewById(R.id.editTextPassword);

    textViewSignin=(TextView) findViewById(R.id.textViewSignin);

    buttonRegister.setOnClickListener(this);
    textViewSignin.setOnClickListener(this);
}

private void registerUser(){
    final String matric=mMatricField.getText().toString().trim();
    final String name= mNameField.getText().toString().trim();
    String email=editTextEmail.getText().toString().trim();
    String password=editTextPassword.getText().toString().trim();

    if(TextUtils.isEmpty(matric)){
        //password is empty
        Toast.makeText(this, "Please enter matric number", Toast.LENGTH_SHORT).show();
        //stopping the function execution further
        return;

    }
    if(TextUtils.isEmpty(name)){
        //password is empty
        Toast.makeText(this, "Please enter your name", Toast.LENGTH_SHORT).show();
        //stopping the function execution further
        return;

    }

    if(TextUtils.isEmpty(email)){
        //email is empty
        Toast.makeText(this,"Please enter email",Toast.LENGTH_SHORT).show();
        //stopping the function execution further
        return;
    }
    if(TextUtils.isEmpty(password)){
        //password is empty
        Toast.makeText(this, "Please enter password", Toast.LENGTH_SHORT).show();
        //stopping the function execution further
        return;

    }
    //if validation are ok
    //we will first show a progressbar

    progressDialog.setMessage("Registering User...");
    progressDialog.show();

    firebaseAuth.createUserWithEmailAndPassword(email,password)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if(task.isSuccessful()){
                        String user_id=firebaseAuth.getCurrentUser().getUid();
                        DatabaseReference current_user_db= mDatabase.child(user_id);
                        current_user_db.child("name").setValue(name);
                        current_user_db.child("matric").setValue(matric);
                        current_user_db.child("image").setValue("default");
                        //user is successfully registered and logged in
                        //we will start the profile activity here
                        //display a toast only
                            finish();
                            startActivity(new Intent(getApplicationContext(),ProfileActivity.class));
                        Toast.makeText(MainActivity.this, "Registered Successfully", Toast.LENGTH_SHORT).show();
                    }else{
                        Toast.makeText(MainActivity.this, "Could not register... Please try again", Toast.LENGTH_SHORT).show();

                    }
                }
            });
}

@Override
public void onClick(View view) {
    if(view== buttonRegister){
        registerUser();
    }
    if(view== textViewSignin){
        //will open login activity here
        startActivity(new Intent(this, LoginActivity.class));
    }

}