I'm still not clear on Case 1:
Do you mean that if *another* row exists with HKD/USD then that combination is not acceptable in the current row ?

(Let's leave Q2 until I'm clear on Q1 :-} )

>sorry i say not clear. question 1. currency exchange rate talbe( Currid currid2 exrate) .
> -------------------------------------------
> HKD USD 7.8
> case 1. if current entry HKD in currid is ok , but if entry HKD in currid and USD in currid2 , then will pop message, because already exits.
> case 2. if current entry HKD in currid is ok, but if entry HKD in currid and HKD in currid2, then also pop messge,because can't convert rate.
>
>
>question 2.
> Why i use DataGridViewComboBoxColumn control, i can't use e.FormattedValue in dg.CellValidating to checking,
> even i select the HKD , then i set break point to see, it also e.FormattedValue =" " .
> How to check DataGridViewComboBoxColumn value.
>
>How can i check this 2 question in dg.CellValidating method.