C# 如何在asp.net中将图表标题显示为dropdownlist选定项

如果我从下拉列表中选择了一个项目，那么它会在图表控件中将文本显示为标题

 <asp:Chart ID="Chart1" runat="server"  Height="350px" Width="600px" Style="text-align: center;
        margin-left: auto; margin-right: auto; ">
        <Titles>

           <asp:Title Font="Times New Roman, 12pt, style=Bold, Italic" Name="Title1" Text="Daily MeatSale Graph" >
           </asp:Title>

       </Titles>

       <Legends>
           <asp:Legend Docking="Bottom" IsTextAutoFit="False" Name="MeatinKgs" LegendStyle="Row" />
       </Legends>
       <Series>
           <asp:Series Name="Meat in Kgs" ToolTip="#VALX [#VALY Kgs]" YValuesPerPoint="1" />
       </Series>
       <ChartAreas>
           <asp:ChartArea Name="ChartArea1">
           </asp:ChartArea>
       </ChartAreas>
   </asp:Chart>

  string s = "Daily MeatSale Graph - " + Request.QueryString["branchname"].ToString();
  Chart1.ChartAreas[0].AxisX.Title = "Dates";
  Chart1.ChartAreas[0].AxisY.Title = "Meat In Kgs";
  Chart1.Titles.Add(s);