If you want to work with the selectedIndex like in a comboBox
1. You have to add your Items to the comboBox element
DataGridViewComboBoxColumn1.Items.Add("your Text ");
DataGridViewComboBoxColumn1.Items.Add("your Text1 ");
DataGridViewComboBoxColumn1.Items.Add("your Text2 ");
2. if you want to set the selectedIndex you have to do it like this
int selectedIndex = 1
DataGridView1.Rows[yourrowIndex].cells["YourcomboBox column"].Value = DataGridViewComboBoxColumn1.Items[selectedIndex];
3 if you want to get the selectedIndex do it like this
int selectedIndex = DataGridViewComboBoxColumn1.Items.IndexOf
(DataGridView1.Rows[yourrowIndex].cells["YourcomboBox column"].Value);
sorry for the delay and my englisch but i hope it will be helpfull