code: private void initializeValidateButton() {
          Button button = (Button) findViewById(R.id.validate_button);
          button.setOnClickListener(new OnClickListener() {
  
              @Override
              public void onClick(final View v) {
                  usernameEditText.validate();
                  passwordEditText.validate();
                  passwordRepetitionEditText.validate();
                  genderSpinner.validate();
                  firstNameEditText.validate();
                  lastNameEditText.validate();
                  additionalInformationEditText.validate();
              }
  
          });
      }
docs: Initializes the button, which allows to validate the values of all views.