Select action on a powershell GUI (windows forms)

Hi

Ive created a Gui with powershell and som list boxes.

What i want to do is, when i select (mouse click on it) an object in my list, i want to show infomation about that object. But i cant find the code for click-select-action.

Here's a pic, ive selected https://intranett,

I have a textfield under where i want to display its size in MB.

all help with be greatly appricated!

br

Bjorn