如何创建下拉列表为一个树列表？（此文为dev控件中，服务器控件暂不知，但想方法应该都差不多吧）

//前端控件代码：
<dx:ASPxDropDownEdit ID="drop_treelist" runat="server" ClientInstanceName="DropDownEdit" Width="280px" NullText="选择商品分类" AllowUserInput="False" AnimationType="None">
                                            <DropDownWindowStyle>
                                                <Border BorderWidth="0px" />
                                            </DropDownWindowStyle>
                                            <ClientSideEvents Init="UpdateSelection" DropDown="OnDropDown" />
                                            <DropDownWindowTemplate>
                                                <div>
                                                    <dx:ASPxTreeList ID="TreeList" ClientInstanceName="TreeList" runat="server" Width="280px" OnCustomJSProperties="TreeList_CustomJSProperties" KeyFieldName="cateid" ParentFieldName="parentid" Theme="Mulberry"
                                                          OnHtmlRowPrepared="TreeList_HtmlRowPrepared">
                                                        <Settings VerticalScrollBarMode="Auto" ScrollableHeight="200" />
                                                        <ClientSideEvents FocusedNodeChanged="UpdateSelection" />
                                                        <BorderBottom BorderStyle="Solid" />
                                                        <Settings ShowColumnHeaders="false" />
                                                        <SettingsBehavior AllowFocusedNode="true" AutoExpandAllNodes="false" FocusNodeOnLoad="false"/>
                                                        <SettingsPager Mode="ShowAllNodes"></SettingsPager>
                                                        <Styles>
                                                            <Node Cursor="pointer"></Node>
                                                            <Indent Cursor="default"></Indent>
                                                            
                                                        </Styles>
                                                        
                                                        <Columns>
                                                            <dx:TreeListTextColumn FieldName="catename"  Caption="分类名称" VisibleIndex="1"></dx:TreeListTextColumn>
                                                            <dx:TreeListTextColumn FieldName="LAYER" Caption="层级" Visible="false"></dx:TreeListTextColumn>
                                                        </Columns>
                                                    </dx:ASPxTreeList>
                                                </div>
                                               
                                            </DropDownWindowTemplate>
                                        </dx:ASPxDropDownEdit>


//如何给其绑定数据并获得选中的树内容放置于显示框中

private void showGoodsListTree()   //绑定数据
{
ASPxTreeList tree = drop_treelist.FindControl("TreeList") as ASPxTreeList;
DataSet ds = new DataSet();
ds = goodsmanagebll.Get_categoriesTreee();
tree.DataSource = ds.Tables[0];
tree.DataBind();
//string n = tree.FocusedNode.GetValue("LAYER").ToString();

}

//通过此事件，可将选中的树值放置显示与下拉框中，还要写js
protected void TreeList_CustomJSProperties(object sender, DevExpress.Web.ASPxTreeList.TreeListCustomJSPropertiesEventArgs e)
{
ASPxTreeList treeList = sender as ASPxTreeList;
Hashtable nameTable = new Hashtable();
//treeList.FocusedNode.ParentNode.AllowSelect = !treeList.FocusedNode.ParentNode.HasChildren;
foreach (TreeListNode node in treeList.GetVisibleNodes())
nameTable.Add(node.Key, string.Format("{0}", node["catename"]));
e.Properties["cpEmployeeNames"] = nameTable;
}

js：

<script type="text/javascript">

//star_商品分类下拉tree选择读取
function UpdateSelection() {
var employeeName = "";
var focusedNodeKey = TreeList.GetFocusedNodeKey();
ASPxCallbackPanel1.PerformCallback(focusedNodeKey);
if (focusedNodeKey != "")
employeeName = TreeList.cpEmployeeNames[focusedNodeKey];
UpdateControls(focusedNodeKey, employeeName);

}
function UpdateControls(key, text) {
DropDownEdit.SetText(text);
DropDownEdit.SetKeyValue(key);
DropDownEdit.GetText() != ""
TreeList.GetFocusedNodeKey() != ""
// DropDownEdit.HideDropDown();
}

function OnDropDown() {
TreeList.SetFocusedNodeKey(DropDownEdit.GetKeyValue());
TreeList.MakeNodeVisible(TreeList.GetFocusedNodeKey());
}
//end_商品分类下拉tree选择读取

function btnClick_save(s, e) {

ASPxCallback1_save.PerformCallback();
}

</script>

效果图：