DropDownList多级,清空数据

C# code

    private void getName()    {                  this.DropDownList1.DataSource =DropDownList1();            this.DropDownList1.DataValueField = "id";            this.DropDownList1.DataTextField = "name";            this.DropDownList1.DataBind();            this.DropDownList1.Items.Insert(0, new ListItem("--请选择--", "0"));            this.DropDownList2.Items.Insert(0, new ListItem("--请选择--", "0"));            this.DropDownList3.Items.Insert(0, new ListItem("--请选择--", "0"));          }//点击第一级获得第二级数据    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)    {          string id = this.DropDownList1.SelectedValue;            this.DropDownList2.DataSource =GetDropDownList2(id);            this.DropDownList2.DataValueField = "id";            this.DropDownList2.DataTextField = "name";            this.DropDownList2.DataBind();            this.DropDownList3.Items.Insert(0, new ListItem("--请选择--", "0"));       }//点击第二级获得第三级数据    protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)    {            string id = this.DropDownList2.SelectedValue;            this.DropDownList3.DataSource = GetDropDownList3(id);            this.DropDownList3.DataTextField = "name";            this.DropDownList3.DataValueField = "id";            this.DropDownList3.DataBind();            this.DropDownList3.Items.Insert(0, new ListItem("--请选择--", "0"));           }

目前重新选择的话第三级的数据还是之前选择第二级所获得的数据
请问重新点击第一级的时候 如何清空第三级的数据 显示--请选择--？



[解决办法]
在选择第一级的时候dropdownlist3.Items.Clear();