c#组合框将项目添加为用户类型文本

需要正确的解决方案：

1. 用户在组合框中键入
2. 每打一封信，都会从互联网上返回一份匹配姓名的列表
3. 组合框下拉列表中已填充项目，组合框中的文本不受影响

我的代码：

    private void InitializeComboBoxSearchSymbol()
    {
        comboBoxSearchName.ValueMember = "first_name";
        comboBoxSearchName.DisplayMember = "first_name";
        comboBoxSearchName.AutoCompleteMode = AutoCompleteMode.None;
        comboBoxSearchName.SelectedIndexChanged += comboBoxSearchName_SelectedIndexChanged;
        comboBoxSearchName.KeyDown += SearchNameTextChanged;
    }

    private void comboBoxSearchName_SelectedIndexChanged(object sender, EventArgs e)
    {
    }
    private void SearchNameTextChanged(object sender, KeyEventArgs e)
    {
        YahooData yd = new YahooData();
        List<Name> listNames = yd.YahooNameLookup(comboBoxSearchName.Text);
        comboBoxSearchName.Items.Clear();
        comboBoxSearchName.Items.AddRange(listNames.ToArray());
    }

上面的代码可以工作，但列表不会被下拉，文本光标会变得奇怪，有时还会抛出错误。

comboBoxSearchName.DroppedDown = true;