Detect if datagrid cell is null/blank

[markyjj01]

Can someone please help me with the following problem. I currently have a datgrid that is linked to an sqlexpress database. The user can change details by clicking on a row and then update any changes through an update button. However, I want to prevent the datagrid from having any blank cells and there should be data in very cell all the time.

Is there a way to keep focus on the cell until data has been entered or any other methods I can use?

Grateful for any advice......cheers.