Single responsability example, step 1

form.cs

private void btnLoad_Click(object sender, EventArgs e)
{
    listView1.Items.Clear();
    var fileName = txtFileName.Text;
    using (var fs = new FileStream(fileName, FileMode.Open))
    {
        var reader = XmlReader.Create(fs);
        while (reader.Read())
        {
            if (reader.Name != "product") continue;
            var id = reader.GetAttribute("id");
            var name = reader.GetAttribute("name");
            var unitPrice = reader.GetAttribute("unitPrice");
            var discontinued = reader.GetAttribute("discontinued");
            var item = new ListViewItem(new string[] { id, name, unitPrice, discontinued });
            listView1.Items.Add(item);
        }
    }
}