Asp.Net c#下拉列表所选索引改变大约需要50到60秒

净webforms。我意识到并得到了许多抱怨。下拉选择的索引需要大量的时间来绑定另一个下拉选择的索引更改做了非常简单的事情，但没有运气。

 <div class="col-sm-4">
                    <div>
                        <asp:Label Text="Category *" ID="LabelCompanyCategory" runat="server"></asp:Label>
                    </div>
                    <div>
                        <telerik:RadComboBox ID="DropDownListCompanyCategory" runat="server"
                            AutoPostBack="true" AppendDataBoundItems="true"
                            Width="100%" CssClass="form-control" CausesValidation="False"
                            DataSourceID="SqlDataSourceCategory" DataTextField="catDescription" DataValueField="CatId"
                            OnSelectedIndexChanged="DropDownListCompanyCategory_SelectedIndexChanged"
                            EmptyMessage="Select Category">
                        </telerik:RadComboBox>
                        <asp:RequiredFieldValidator runat="server" ErrorMessage="please select a category" Display="Dynamic"
                            ControlToValidate="DropDownListCompanyCategory" ForeColor="Red" ID="rfv2"></asp:RequiredFieldValidator>
                        <asp:SqlDataSource ID="SqlDataSourceCategory" ConnectionString='<%$ ConnectionStrings:MainConnection %>' runat="server"
                            SelectCommand=" select CatId, Catdescription from dbo.category"></asp:SqlDataSource>
                    </div>
                </div>
                <div class="col-sm-4" runat="server" id="DivActivity" visible="false">
                    <div>
                        <asp:Label Text="Activity *" ID="LabelCompanyActivity" runat="server"></asp:Label>
                    </div>
                    <div>
                        <telerik:RadComboBox ID="DropDownListActivity" runat="server" CssClass="form-control" Width="100%"
                            AppendDataBoundItems="false" DataSourceID="SqlDataSourceActivity" EmptyMessage="Select Activity" CausesValidation="False"
                            DataTextField="activity" DataValueField="id">
                        </telerik:RadComboBox>
                        <asp:RequiredFieldValidator runat="server" ErrorMessage="please select a Activity"
                            ControlToValidate="DropDownListActivity" ForeColor="Red" Display="Dynamic" ID="RequiredFieldValidator1"></asp:RequiredFieldValidator>
                    </div>
                    <asp:SqlDataSource ID="SqlDataSourceActivity" ConnectionString='<%$ ConnectionStrings:MainConnection %>' runat="server"
                        SelectCommand="select activity, id from activity where catid=@CategoryId">
                        <SelectParameters>
                            <asp:ControlParameter ControlID="DropDownListCompanyCategory" PropertyName="SelectedValue"
                                DefaultValue="0" Name="CategoryId" />
                        </SelectParameters>
                    </asp:SqlDataSource>
                </div>

后端代码:

 protected void DropDownListCompanyCategory_SelectedIndexChanged(object sender, EventArgs e)
{
    DivActivity.Visible = true;
    DropDownListActivity.DataBind();
}