Datagrid selected cell content

Hi

I want open a dialog windows depending of cell in a row:
E.g:
[1] | [2] [3]
[4] | [5] [6]
click on clell [5] a dialog open with param Id=5 ...

On only find RowClick, but than I do not know, does the user select 1,2,3

Thx
Claus