I have the code which i used to check duplication in listbox but not working?

Q. I have 3 columns in listview grid and i want to check duplication with only one field. How to do that?


Code:
if(listView1.Items.Contains(lvi) == false)
{
//Add the item to the ListView Control
listView1.Items.Add(lvi);
}
else
{
//Warn user of duplicate entry...
MessageBox.Show("Duplicate Item!");
}
Thanks, Please help