Modifying data after user change data in GRID

Hello together,

I am writing a form in Dynamics AX 4.0. I use a GRID for represent the data. The user can change the data in the GRID.

Now I want do the following.

If the user change a field in the grid for example the itemNumber I want update another field of the same data record. ’

For this I have tried to use the modifed() method of the data source, but I have no idea if this is the correct way.
With the modified method of the data source I have the problem that I do not know, how I get the data record which I wanna change. I do not find a possibliy to find the data record over the “THIS”-reference´.

What is the common way for opperations like this?

Have someone some code sample?

Best regards