I have solved this issue by the following code. Thanks for all ...
public static void ComboBoxFill(ComboBox cbo, string Query, string cboDisplayMember, string cboValueMember)
{
con.Open();
SqlCommand cmd = new SqlCommand(Query, con);
SqlDataReader dr = cmd.ExecuteReader();
DataTable dt = new DataTable();
dt.Load(dr);
DataRow drow = dt.NewRow();
for (int i = 0; i < dt.Columns.Count ; i++)
{
if (dt.Columns[i].ColumnName == cboDisplayMember)
{
drow[i] = "Select";
}
else if (dt.Columns[i].ColumnName == cboValueMember)
{
drow[i] = 0;
}
else
{
drow[i] = null;
}
}
dt.Rows.InsertAt(drow, 0);
cbo.DataSource = dt;
cbo.DisplayMember = cboDisplayMember;
cbo.ValueMember = cboValueMember;
cbo.SelectedIndex = 0;
con.Close();
}