problem on oledbparameter on asp.net

private void Update_data(Object sender, DataGridCommandEventArgs e)
{
try
{
String updateCmd = "update rohsdb set Supplier=? where PortNo=?";
OleDbConnection myConnection= new OleDbConnection("Provider=MSDAORA; Data Source=***;User ID=system;Password=***");
OleDbCommand myCommand = new OleDbCommand(updateCmd,myConnection);

myCommand.Parameters.Add(new OleDbParameter("@PortNo",OleDbType.VarChar,50));
myCommand.Parameters["@PortNo"].Value= DataGrid1.DataKeys[(int)e.Item.ItemIndex];

myCommand.Parameters.Add(new OleDbParameter("@Supplier",OleDbType.VarChar,50));
myCommand.Parameters["@Supplier"].Value= ((TextBox)e.Item.FindControl("edit_supplier")).Text;

myConnection.Open();
myCommand.ExecuteNonQuery();
DataGrid1.EditItemIndex=-1;
Show_data();

}
catch(System.InvalidCastException d)
{
Message.Text="Update failed" + d.ToString();
}

}

when running the program, no error occurs. but the data can not be updated. i don't know why.( i am using oracle server)

can anyone help me?

 

try changing:
String updateCmd = "update rohsdb set Supplier=? where PortNo=?";
to
String updateCmd = "update rohsdb set Supplier=@Supplier where PortNo=@PortNo";