I would like use combox for drop-down list.
ASPX Code
<ext:Store ID="StockRoomListStore" runat="server">
        <Reader>
            <ext:JsonReader>
                <Fields>
                    <ext:RecordField Name="StockroomID" Type="String">
                    </ext:RecordField>
                    <ext:RecordField Name="StockChinName" Type="String">
                    </ext:RecordField>
                </Fields>
            </ext:JsonReader>
        </Reader>
    </ext:Store>

<ext:ComboBox ID="cmbStockRoomOut" runat="server" StoreID="StockRoomListStore" DataIndex="StockRoomID_Out"
                         Note="StockRoomOut" Mode="Local" ListWidth="160px" DisplayField="StockChinName"
                          ValueField="StockroomID" ItemSelector="tr.Stockroomlist-item">
  <Template ID="Template5" runat="server">
    <Html>
      <tpl for=".">
    <tpl if="[xindex] == 1">
    <table class="StockRoomlist">
    </tpl>
        <tr class="Stockroomlist-item">
    <td style="padding:6px 0px;">{StockChinName}</td>
    </tr>
    <tpl if="[xcount-xindex]==0">
    </table>
    </tpl>
    </tpl>
        </Html>
        </Template>
        <Triggers>
           <ext:FieldTrigger Icon="Clear" HideTrigger="true" />
        </Triggers>
        <Listeners>
           <BeforeQuery Handler="this.triggers[0][ this.getRawValue().toString().length == 0 ? 'hide' : 'show']();" />
           <TriggerClick Handler="if (index == 0) { this.focus().clearValue(); trigger.hide();}" />
           <Select Handler="{this.triggers[0].show();}" />
         </Listeners>
</ext:ComboBox>
Code Behind：
protected void Page_Load(object sender, EventArgs e)
{
    if (!X.IsAjaxRequest) 
    { 
    StockRoomListStore.DataSource = GetStockroomList();
    StockRoomListStore.DataBind();
    }
}
private List<JsonObject> GetStockroomList()
{

    DbCommand sql = _manageLogic.StockRoomList();///Get StockRoomList from SQL
    DataTable sourcetbl = sql.FillTable();
    if (sourcetbl == null || sourcetbl.Rows.Count == 0)
        return null;
    string json = _manageLogic.GetJSON(sourcetbl); ///Transfer DataTable Structure into JSON 
    List<JsonObject> list = JSON.Deserialize<List<JsonObject>>(json);
    
    return list;
            
}
public string GetJSON(DataTable dt)
{
    StringBuilder sb = new StringBuilder();
    ///sb.Append("{\"totalCount\":" + dt.Rows.Count + ",\"data\":");
    sb.Append("[");
    try
    {
        if (dt.Rows.Count > 0)
        {
            Hashtable ht = new Hashtable();
            for (int i = 0; i < dt.Columns.Count; i++)
            {
                ht.Add(i, dt.Columns[i].ColumnName);
            }
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                sb.Append("{");
                for (int j = 0; j < dt.Columns.Count; j++)
                {
                    sb.Append(string.Format("\"{0}\":\"{1}\",",
                    ht[j], dt.Rows[i][j].ToString()));
                }
                sb.Remove(sb.ToString().LastIndexOf(","), 1);
                sb.Append("},");
            }
            sb.Remove(sb.ToString().LastIndexOf(","), 1);
            ht.Clear();
            ht = null;
        }
    }
    catch (Exception ex)
    {
        throw new Exception(ex.Message);
    }
    finally
    {
        ///sb.Append("]}");
        sb.Append("]");
    }
    return sb.ToString();
}
But my combobox shosw nothing. I wonder if my datasource type was wrong or other reason ????