C#

listview.Items.Add("aaaa");
listview.Items[index].SubItems.Add("bbbb");

listview.Items[index]

public class DataItem
{
  private int key;
  private string name;
  public DataItem() : this(0, null)
  {
  }
  public DataItem(int key, string name)
  {
    this.key = key;
    this.name = name;
  }
  public int Key
  {
    get { return key; }
    set { key = value; }
  }
  public string Name
  {
    get { return name; }
    set { name = value; }
  }
}

listBox1.Items.Add(
  new DataItem(1, "Test 1"));

DataItem data = listBox1.Items[0];
data.Name = "Something new";