User wants to navigate to a another cell
The CanSelectCurrentCell method is called from Objective Grid before grid deactivates the previous current cell and again before the grid activates the new current cell. CanSelectCurrentCell is called with the coordinates of the old and the new current cell. If you return FALSE the grid will abort moving the current cell.
Another more powerful method that you can override is SetCurrentCell. SetCurrentCell is the method in Objective Grid that is responsible for positioning the current cell. SetCurrentCell is called before CanSelectCurrentCell. Actually, SetCurrentCell will call CanSelectCurrentCell and check the return value.