Combobox实现多项选择 Silverlight下“Combobox”怎样实现多项选择？

combobox cbb=new combobox();
if (null != ItemList && ItemList.Count > 0)
{
CheckBox cb = new CheckBox();
cb.CommandParameter = cbb.Name;
cb.Tag = "check_All";
cb.Content = "全部选择";
cb.Click += new RoutedEventHandler(cb_Click);
cbb.Items.Add(cb);
foreach (var dr in ItemList)
{
cb = new CheckBox();
cb.CommandParameter = cbb.Name;
cb.Tag = dr.FLID;
cb.Content = dr.Gradation;
cb.Click += new RoutedEventHandler(cb_Click);
cbb.Items.Add(cb);
}
}

DataModel 这是张表，表中包含FLID和Gradation两个字段
List<DataModel> ItemList=new List<DataModel> ();
然后往ItemLIst中添加数据就OK～～～