Datagrid validation..

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C#

hi..
i want to check weather datagrid particular cell is empty. what i wantto do is :
if in a datagrid row if 1st 2 cells are not null and if i did not enter a value to 3rd cell then i go to enter new values to next row then i want o give error fill the 3rd cell.
so far what i did was:
here dgvItem is my datagrid. i have written this code in cell_enter event

try
             {
                 if (dgvItem.CurrentCell.ColumnIndex == 1)
                 {
                 //for (int i = 0; i < dgvItem.Rows.Count+1; i++)
                // if (dgvItem.CurrentRow.Index==0)
                 //{
  
                     string itemDis;
                     itemDis = Convert.ToString(dgvItem.CurrentRow.Cells[1].Value);
                     //itemDis = Convert.ToString(dgvItem.Rows[i].Cells[1].Value);
                     string itemQty;
                     itemQty = Convert.ToString(dgvItem.CurrentRow.Cells[3].Value);
                     //itemQty = Convert.ToString(dgvItem.Rows[i].Cells[3].Value);
                     if (itemDis != "" && itemQty == "")
                     {
                         DialogResult reply = MessageBox.Show("Please Fill the data", "", MessageBoxButtons.OK, MessageBoxIcon.Error);
                         if (reply == DialogResult.OK)
                         {
                             dgvItem.Focus();
                         }
                     }
                 }
            }
             catch { }

i have tried many ways to do this as i have comment in the code above. but the message is coming when ever i click on the cell.
meaning my 1st cell is a combobox.so when i click on the 2nd cell relevent value for combobox selected value have to fill to 2nd cell. so even when i clik on 2nd cell before even go to next row the message is comming.

so what can i do ?? how can i do this. i hope what im asking is clear over here?

thank you