private void AdminHome_Load(object sender, EventArgs e) { AutoCompleteStringCollection coll = new AutoCompleteStringCollection(); UpdateDBLin ul = new UpdateDBLin(); List <string> li = ul.getAllUser(); for (int i = 0; i < li.Count(); i++) { coll.Add(li.ElementAt(i).ToString()); } textBox1.AutoCompleteCustomSource = coll; }