Checkbox showing tristate in datagrid

Question

Hi, I have populated the values in to the grid. one column is bool type and hence it shows checkbox in it. i tried to toggle the value of the checkbox in the runtime. but when i click on the box when it is checked, it goes into tristate mode (a shade on te check box), then again when i clieked it unchecked, and again it checked for next click. i dont want the tristate behaviour. suggestions please Ram