Hello I have this program in which I need to calculate a price of something. This is easily done, however I don't want to calculate the price in the GUI, coz that would be a huge waste of CPU to calculate it 1000 times each second. Is there some kind of method to know and react to change in dropdown menues? Example: User changes value of dropdown / writes own value in an input field. Then, and only then, will the function be called that does the calculating.