ValueChangeListener<String> mandatoryChangeListener = new ValueChangeListener<String>() {
    private static final long serialVersionUID = 1L;

    @Override
    public void valueChange(ValueChangeEvent<String> event) {
        log.debug("mandatoryChangeListener.addValueChangeListener");
        checkButtonState();
    }
};

protected void registerMandatoryInputs() {

    //registerMandatoryInput(kpiCategories.cbExtraInfo, mandatoryChangeListener);
    registerMandatoryInput(tKpiDescription, mandatoryChangeListener);
    registerMandatoryInput(tKpiName, mandatoryChangeListener);
    registerMandatoryInput(tFrequency, mandatoryChangeListener);
    registerMandatoryInput(cbFrequencyUnit, mandatoryChangeListener);
    registerMandatoryInput(cbBusinessProcess, mandatoryChangeListener);
    registerMandatoryInput(cbBusinessEvent, mandatoryChangeListener);

    kpiThresholds.registerMandatoryInputs(mandatoryChangeListener);
}

@SuppressWarnings("unchecked")
protected void registerMandatoryInput(Component c, ValueChangeListener<String> listener) {
    if(c instanceof TextField) {
        ((TextField) c).addValueChangeListener(listener);
    } else if(c instanceof ComboBox) {
        ((ComboBox<String>) c).addValueChangeListener(listener);
    } else if(c instanceof TextArea) {
        ((TextArea) c).addValueChangeListener(listener);
    } else {
        log.info("Component could not be registered as mandatory: " + c.getClass().toString());
    }
}
private boolean inCheckButtonState = false;
protected void checkButtonState() {
    log.debug("checkButtonState ..");
    if(!inCheckButtonState) {
        inCheckButtonState = true;

        boolean okEdit = checkMandatoryFields();
        boolean okThresholds = kpiThresholds.validateMandatoryFields() && !mustHaveClickedOnThresholdsButton;
        if( okEdit && okThresholds) {
            log.debug("checkButtonState enable ..");
            enableButton(bSaveKpi);
            enableButton(bUpdateKpi);

            enableButton(bSaveKpiThresholds);
            enableButton(bUpdateKpiThresholds);

            enableButton(bEnable);
            enableButton(bDisable);
        } else {
            log.debug("checkButtonState disable ..");
            disableButton(bSaveKpi);
            disableButton(bUpdateKpi);

            disableButton(bSaveKpiThresholds);
            disableButton(bUpdateKpiThresholds);

            disableButton(bEnable);
            disableButton(bDisable);
        }

        if(okEdit) {
            log.debug("checkButtonState enable Navigation..");
            enableButton(bToThresholds);
        } else {
            log.debug("checkButtonState disable Navigation..");
            disableButton(bToThresholds);
        }

        if(okThresholds) {
            log.debug("checkButtonState enable Navigation back..");
            enableButton(bBackToEdit);
            bToThresholds.setComponentError(null);
        } else {
            log.debug("checkButtonState disable Navigation back..");
            disableButton(bBackToEdit);
            if(mustHaveClickedOnThresholdsButton) {
                String clickMessage = messageByLocaleService.getMessage("message.checkthresholds");
                bToThresholds.setComponentError(new UserError(clickMessage));
            } else {
                bToThresholds.setComponentError(null);
            }
        }
    }
    inCheckButtonState = false;
}

protected static void disableButton(Button b) {
    b.addStyleName("test-data");
    b.setEnabled(false);
}

protected static void enableButton(Button b) {
    b.removeStyleName("test-data");
    b.setEnabled(true);
}