如何使telerik自动完成文本框在c# winforms中只接受1项输入

private void Form_Load(object sender, EventArgs e)
{
    radAutoCompleteBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
    radAutoCompleteBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
    radAutoCompleteBox1.AutoCompleteCustomSource = new AutoCompleteStringCollection();
}

private void radAutoCompleteBox1_TextChanged(object sender, EventArgs e)
{
    if (radAutoCompleteBox1.Text.Length > 0)
    {
        radAutoCompleteBox1.AutoCompleteCustomSource.Clear();
        radAutoCompleteBox1.AutoCompleteCustomSource.Add(radAutoCompleteBox1.Text);
    }
}

private void radAutoCompleteBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (radAutoCompleteBox1.AutoCompleteCustomSource.Contains(radAutoCompleteBox1.Text))
    {
        e.Handled = true;
    }
}