public HandlerRegistration addShowRangeHandlerAndFire(
            ShowRangeHandler<UTCDate> handler) {
        ShowRangeEvent<UTCDate> event = new ShowRangeEvent<UTCDate>(
                getView().getFirstDate(), getView().getLastDate()) {
        };
        handler.onShowRange(event);
        return addShowRangeHandler(handler);
    }
Adds a show range handler and immediately activate the handler on the
current view.

@param handler the handler
@return the handler registration
stroom-core-client-widget/src/main/java/stroom/widget/datepicker/client/CustomDatePicker.java