private FirebaseAuth auth;

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

    }

    @Override
    protected void onStart() {
        super.onStart();
        FirebaseUser currentUser = auth.getCurrentUser();
    }


    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            // signUpTextView ID
            case R.id.signUpId:
                startActivity(new Intent(this, SignUpActivity.class));
        }
    }


    // REGISTER USER ACTIVITY

    EditText editTextEmail;
    EditText editTextPassword;

    // Progress bar
    ProgressBar progressBar;

    // onCreate metoda v register ACTIVITY
    /*

        super...
        setcontent..

        editTextEmail = (EditText) findViewById(R.id.editTextEmail);
        editTextPassword = (EditText) findViewById(R.id.editTextPassword);

        auth = FirebaseAuth.getInstance();

        findViewById().setOnClickListener(this); // SIGN UP
        progressBar = (ProgressBar) findViewById(R.id.progressBar);






     */

    private void registerUser() {
        String email = editTextEmail.getText().toString().trim();
        String password = editTextPassword.getText().toString().trim();

        if (email.isEmpty()) {
            editTextEmail.setError("Email is requiered");
            editTextEmail.requestFocus();
            return;
        }

        if(!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            editTextEmail.setError("Please enter a valid email");
            editTextEmail.requestFocus();
            return;
        }


        if (password.isEmpty()) {
            editTextPassword.setError("Email is requiered");
            editTextPassword.requestFocus();
            return;
        }

        if(password.length()) {
            editTextPassword.setError("Minimum length of password should be 6");
            editTextPassword.requestFocus();
            return;
        }

        progressBar.setVisibility(View.VISIBLE);

        auth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                progressBar.setVisibility(View.GONE);
                if(task.isSuccessful()) {
                    Toast.makeText(getApplicationContext(), "User Registered Successfull", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(getApplicationContext(), "Some error occured", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    public void onClick(View view) {
        switch (view.getId()) {
            // signUp button
            case R.id.buttonSignUp:
                registerUser();
                break;

            // logIn button
            case R.id.textViewLogin:
                startActivity(new Intent(this, MainActivity.class));
                break;
        }
    }