winform中textbox提示框

在winform中向textbox输入内容时下面有提示信息，效果如图所示：

        private void Form1_Load(object sender, EventArgs e)

        {

            AutoCompleteStringCollection strings = new AutoCompleteStringCollection();

            strings.Add("A1");//不区分大小写

            strings.Add("A2");

            strings.Add("Aas");

            strings.Add("B1");

            strings.Add("Beijing");

            strings.Add("bb-cims");

            textBox1.AutoCompleteCustomSource = strings;

            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;

            textBox1.AutoCompleteMode = AutoCompleteMode.Suggest;

        }