C# TextBox 자동 완성

1. Collection Add AutoCompleteStringCollection autoCollection = new AutoCompleteStringCollection(); // Collection 하나씩 추가 autoCollection.Add("Collection1"); autoCollection.Add("Collection2"); autoCollection.Add("Collection3"); //Collection 배열로 추가 autoCollection.AddRange(new string[] { Collection1, Collection2, Collecion3 }); textBox1.AutoCompleteCustomSource = autoCollection; textBox1.AutoCompleteMod = AutoCompleteMod.SuggestAppend; textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource; 2. DB에 있는 것으로 채우기 private void Form1_Load(object sender, EventArgs e)         {             AutoCompleteStringCollection autoCollection1 = new AutoCompleteStringCollection();             AutoCompleteStringCollection autoCollection2 = new AutoCompleteStringCollection();             //comboBox 외박사유             SqlDataAdapter sqlDataAdapterSayu = new SqlDataAdapter("select memo from sayu", conn);             SqlCommandBuilder sqlCommandBuilderSayu = new SqlCommandBuilder(sqlDataAdapterSayu);             DataTable dataTableSayu = new DataTable();             sqlDataAdapterSayu.Fill(dataTableSayu);             BindingSource bindingSorceSayu = new BindingSource();             bindingSorceSayu.DataSource = dataTableSayu;             comboBox1.DataSource = bindingSorceSayu;             comboBox1.ValueMember = "memo";             comboBox1.DisplayMember = "memo";             // TextBox 자동채우기                SqlDataReader reader;             SqlCommand cmd = new SqlCommand();             cmd.Connection = conn;             cmd.CommandType = CommandType.Text;             cmd.CommandText = "select UserName, PersonID from Users";                         conn.Open();             reader = cmd.ExecuteReader();             if (reader.HasRows == true)             {                 while (reader.Read())                 {                     autoCollection1.Add(reader["UserName"].ToString());                     autoCollection2.Add(reader["PersonID"].ToString());                 }             }             reader.Close();             // textBox2 이름             textBox2.AutoCompleteMode = AutoCompleteMode.Suggest;             textBox2.AutoCompleteSource = AutoCompleteSource.CustomSource;             textBox2.AutoCompleteCustomSource = autoCollection1;                         //textBpx1 방번호             textBox1.AutoCompleteMode = AutoCompleteMode.Suggest;             textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;             textBox1.AutoCompleteCustomSource = autoCollection2;