Hi Youssef,
As i mentioned in my other post:
https://forum.mendix.com/link/questions/107305
Put a non Persistable enitity. Then in the page you have attched, put a Data view with Datasource as microlfow and perform the calcluation in the DsMicroflow and return the NPE . When ever you ar changing a Value refresh the Objects so that DS microflow is trigered again.