Listview items not showing

The following code should work:

ColumnHeader columnHeader1=new ColumnHeader();
columnHeader1.Text="Column1";
this.listView1.Columns.AddRange(new ColumnHeader[] { columnHeader1 });
ListViewItem item = new ListViewItem("1");
this.listView1.Items.Add(item);
this.listView1.View = View.Details;

If it doesn't I have no clue. Are the characters of the string you are adding visible?

Are you calling "Clear"? If so make sure you are calling lv.Items.Clear() and not lv.Clear().