C# 删除下拉框中的重复项

private void bindCmbProject()//绑定项目总称 下拉框
{
this.cmbProName.Items.Clear();
cmbProName.Items.Add(string.Empty);//添加空项
ProjectHelper ProH = new ProjectHelper();
DataSet ds = ProH.selectProName();//操作数据表获取表Table
for (int lenth = 0; lenth < ds.Tables[0].Rows.Count; lenth++)
{
cmbProName.Items.Add(ds.Tables[0].Rows[lenth]["AAA006"]);
}
RemoveRepeatItem(cmbProName);//<span style="font-family: Arial, Helvetica, sans-serif;">删除下拉框中的重复项 只保留一个</span>

cmbProName.SelectedIndex = 0;//默认为空
}

private void RemoveRepeatItem(ComboBox cbb)
{
List<string> list = new List<string>();
foreach (string s in cbb.Items)
{
if (!list.Contains(s))
{
list.Add(s);
}
}
cbb.Items.Clear();
foreach (string s in list)
{
cbb.Items.Add(s);
}
}