public void onRegisterClick(View v) {
	progressBar.setVisibility(View.VISIBLE);
	progressBar.animate().alpha(1).setDuration(500).start();
	final String username = usernameEditText.getText().toString();
	final String password = passwordEditText.getText().toString();
	RegistrationDTO dto = new RegistrationDTO(username, password);
	registrationService.callback(new Callback() {
		@Override
		public void onResponse(Call<RegistrationDTO> call, Response<RegistrationResult> response) {
			progressBar.setVisibility(View.GONE);
			storage.putString(USERNAME, username);
			storage.putString(PASSWORD, password);

			Intent nextActivity = new Intent(RegistrationActivity.this, NextActivity.class);
			nextActivity.launch();
		}

		@Override
		public void onFailure(Throwable t) {
			progressBar.setVisibility(View.GONE);
			if (t instanceof ConnectException) {
				new CustomAlertDialog.Builder()
					.setMessage("Internet unavailable")
					.build()
					.show();
			}
			else {
				new CustomAlertDialog.Builder()
					.setMessage("An unknown error has occurred")
					.build()
					.show();
			}
		}
	}).enqueue();
}