C#

public class ListViewItem<T> : ListViewItem
{
    private T data;

    public T Data
    {
        get { return data; }
        set { data = value; }
    }

    public static IEnumerable<ListViewItem<T>> GetListViewSelectedItems(ListView listView)
    {
        return listView.SelectedItems.Cast<ListViewItem<T>>();
    }
}

ListViewItem<string> itemA = new ListViewItem<string>();
itemA.Data = "a";
itemA.Text = "A";
ListViewItem<string> itemB = new ListViewItem<string>();
itemB.Data = "b";
itemB.Text = "B";
listView.Items.Add(itemA);
listView.Items.Add(itemB);

IEnumerable<ListViewItem<string>> selectedItems = 
    ListViewItem<string>.GetListViewSelectedItems(listView);