ControlsFX: Validation on Button click

Question

I am trying to validate two Textfields in javafx on a button click, I am using ControlsFX to do this. Here is my validation code:

private void applyValidationSupprot() {
    ValidationSupport support = new ValidationSupport();

    support.registerValidator(userName, false, (Control control, String value) ->
            ValidationResult.fromErrorIf(userName, "Required", isValid)
    );
    support.registerValidator(password, false, (Control control, String value) ->
            ValidationResult.fromErrorIf(password, "Required", isValid)
    );
}

userName and password are my Textfields and isValid is a variable declared previously, and my button's onAction event is bound to this method:

public void validate() {
    isValid = true;
}

But when I click the button the validation do not happen. Where is the problem?

Reminder: I do not how to make validation with createEmptyValidator but I want my validation to happen on my button click.