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：

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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;

}