string[] arr = new string[listbox.Items.Count];  listbox.Items.CopyTo(arr, 0);    var arr2 = arr.Distinct();   listbox.Items.Clear();    foreach (string s in arr2)    {       listbox.Items.Add(s);    }

 var _items = this.listBox1.Items.Cast<string>().Distinct().ToArray();
 this.listBox1.Items.Clear();
            foreach (var item in _items)
            {
                this.listBox1.Items.Add(item);
            }