当运行代码时，我的文本框没有填写，此代码在我的模态代码中，因此内部有一个更新面板，用户选择ddlid。如果用户选择了一个特定的id，数据库中的一列将被显示并填入txtType，但是当我运行代码时，我放了一个断点，它是成功的，但是在我的网页中，它没有显示结果甚至显示在我的代码中。我的代码有什么问题？
这是我的aspx代码
<asp:UpdatePanel ID="panel1" runat="server">
<ContentTemplate>
<asp:GridView ID="gvModal" runat="server" AutoGenerateColumns="false" DataKeyNames="ID" EmptyDataText="No Records" AllowPaging="true" CellPadding="4" HeaderStyle-BackColor="CornflowerBlue" BorderWidth="2" BorderColor="CornflowerBlue" Width="100%" CssClass="table table-hover" >
<Columns>
<asp:TemplateField HeaderText ="ID" HeaderStyle-ForeColor="White">
<ItemTemplate>
<asp:Label ID="lblID" runat="server" Text='<%#Bind ("ID") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Type" HeaderStyle-Width="20%" ItemStyle-Width="20%" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri" >
<ItemTemplate>
<asp:Label ID="lbltype" runat="server" Text='<%#Bind ("ItemType") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Model" HeaderStyle-Width="30%" ItemStyle-Width="30%" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblModel" runat="server" Text='<%# Bind("ItemModel") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Requested Quantity" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblQuan" runat="server" Text='<%#Bind ("ItemQuantity") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="AMS Actual Balance" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblActual" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Incoming Stock" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblIncoming" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="AMS Issuable Balance" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblAMs" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Unit" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblUnit" runat="server" Text='<%#Bind ("ItemUnit") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Date Needed" HeaderStyle-Width="15%" ItemStyle-Width="15%" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblDate" runat="server" Text='<%#Bind ("ItemDate" , "{0:yyyy-MM-dd}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Description" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblDesc" runat="server" Text='<%#Bind ("ItemDesc") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Status" ItemStyle-Width="10%" HeaderStyle-Width="10%" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblStatus" runat="server" Text='<%#Bind ("ItemStatus") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="PO Number" HeaderStyle-ForeColor="White" ItemStyle-Width="120px" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblPONumber2" runat="server" Text='<%#Bind ("PO_Num") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="PO Date" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblPODate2" runat="server" Text='<%#Bind ("PO_Date", "{0:yyyy-MM-dd}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Delivery Date" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblDelDate2" runat="server" Text='<%#Bind ("Delivery_Date", "{0:yyyy-MM-dd}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Issuance Date" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblIssDate2" runat="server" Text='<%#Bind ("IssuanceDate", "{0:yyyy-MM-dd}") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText ="Issuance Number" HeaderStyle-ForeColor="White" ItemStyle-Font-Names="Calibri" HeaderStyle-Font-Names="Calibri">
<ItemTemplate>
<asp:Label ID="lblIssNum2" runat="server" Text='<%#Bind ("IssuanceNumber") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Last Issuance" ItemStyle-Font-Names="Calibri" HeaderStyle-ForeColor="White" HeaderStyle-BackColor="#336699" ItemStyle-Width="150px">
<ItemTemplate>
<asp:Label ID ="lblIssued" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Quantity" HeaderStyle-ForeColor="White" HeaderStyle-BackColor="#336699" ItemStyle-Font-Names="Calibri" ItemStyle-Width="10px">
<ItemTemplate>
<asp:Label ID ="lblQuantity" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Unit" HeaderStyle-ForeColor="White" HeaderStyle-BackColor="#336699" ItemStyle-Font-Names="Calibri" ItemStyle-Width="20px">
<ItemTemplate>
<asp:Label ID ="lblUnits" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Edit" HeaderStyle-ForeColor="White" HeaderStyle-BackColor="#336699" ItemStyle-Font-Names="Calibri" ItemStyle-Width="80px">
<ItemTemplate>
<asp:DropDownList ID="ddlEditModel" CssClass="form-control" runat="server" AutoPostBack="true"></asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<div class="form-inline">
 <label class="control-label" style="font-family:Calibri">Item ID: </label>  
<asp:DropDownList ID="ddlID" runat="server" CssClass="form-control" Width="5%" AppendDataBoundItems="true" OnSelectedIndexChanged="ddlID_SelectedIndexChanged" AutoPostBack="true"><asp:ListItem Selected disabled>Item #</asp:ListItem></asp:DropDownList> 
<label class="control-label" style="font-family:Calibiri">Type: </label>
<asp:TextBox ID="txtType" runat="server" CssClass="form-control" Width="50%"></asp:TextBox>
<label class="control-label" style="font-family:Calibri">Model: </label>
<asp:DropDownList ID="ddlModel" runat="server" DataSourceID="ModelSource" DataTextField="Model" DataValueField="Model" AutoPostBack="true"></asp:DropDownList>
<asp:SqlDataSource ID="ModelSource" runat="server" ConnectionString="<%$ ConnectionStrings:POConnectionString2 %>" SelectCommand="SELECT DISTINCT Model from ItemType WHERE (Type = @Type) Order By Model">
<SelectParameters>
<asp:ControlParameter Name="Type" ControlID="txtType" />
</SelectParameters>
</asp:SqlDataSource>
</div>
</div>
</ContentTemplate>
</asp:UpdatePanel>
和我的.cs代码
protected void ddlID_SelectedIndexChanged(object sender, EventArgs e)
{
Utility u = new Utility();
string conn = u.PO();
SqlConnection connUser = new SqlConnection(conn);
SqlCommand cmd = connUser.CreateCommand();
SqlDataReader sdr = null;
string que = "SELECT ItemType FROM ItemTransaction WHERE ID ='" + ddlID.SelectedValue + "'";
connUser.Open();
cmd.CommandText = que;
sdr = cmd.ExecuteReader();
string type = "";
while (sdr.Read())
{
type = sdr.GetString(0);
}
txtType.Text = type;
}