下拉列表不会从数据库中polpuate值

Question

我遇到了一个问题，即使用只读模式下的项目字段模板来填充具有来自数据库的值的DropDownList控件。我很欣赏详细的解释，因为我是ASP.NET的新手。下面是代码和我得到的错误：

'PictureReadOnlyCategories'有一个SelectedValue，它是无效的，因为它不存在于项目列表中。 参数名称：值说明：执行当前Web请求期间发生未处理的异常。请查看堆栈跟踪以获取有关该错误的更多信息以及源代码的位置。

异常详细信息：System.ArgumentOutOfRangeException：'PictureReadOnlyCategories'具有无效的SelectedValue，因为它不存在于项目列表中。 参数名：价值

这个代码是：

<asp:SqlDataSource ID="categoriesDataSource" runat="server" 
    ConnectionString="<%$ ConnectionStrings:ConnectionString %>" 
    SelectCommand ="SELECT [CategoryID], [Name] FROM [Categories] WHERE ([UserId] = @UserId)"> 
    <SelectParameters> 
     <asp:ControlParameter ControlID="UserIdValue" 
           Name="UserId" 
           PropertyName="Text" /> 
    </SelectParameters> 
</asp:SqlDataSource> 

<asp:Label ID="UserIdValue" runat="server" Visible="False"></asp:Label> 

<asp:GridView ID="gvPictures" 
       runat="server" 
       AllowPaging="True" 
       AllowSorting="True" 
       AutoGenerateColumns="False" 
       CellPadding="4" 
       DataKeyNames="PictureID" 
       DataSourceID="picturesDataSource" 
       ForeColor="#333333" 
       GridLines="None" Width="800px"> 
    <AlternatingRowStyle BackColor="White" /> 
    <Columns> 
     <asp:CommandField ShowDeleteButton="True" 
          ShowEditButton="True" 
          ValidationGroup="PictureEdit" /> 
     <asp:TemplateField HeaderText="Category" 
          SortExpression="CategoryID"> 
      <EditItemTemplate> 
       <asp:DropDownList ID="pictureEditCategories" 
            runat="server" 
            AppendDataBoundItems="True" 
            DataSourceID="categoriesDataSource" 
            DataTextField="Name" 
            DataValueField="CategoryID" 
            SelectedValue='<%# Bind("CategoryID") %>'> 
        <asp:ListItem Value="" Text="--Select Category -- "/> 
       </asp:DropDownList> 
      </EditItemTemplate> 
      <ItemTemplate> 
       <asp:DropDownList ID="PictureReadOnlyCategories" 
            runat="server" 
            AppendDataBoundItems="True" 
            DataSourceID="categoriesDataSource" 
            DataTextField="Name" 
            DataValueField="CategoryID" 
            Enabled="False" 
            SelectedValue='<%# Bind("CategoryID") %>'> 
        <asp:ListItem Selected="True" Value="">-- No Category --</asp:ListItem> 
       </asp:DropDownList> 
      </ItemTemplate> 
     </asp:TemplateField> 
     <asp:TemplateField HeaderText="Title" SortExpression="Title"> 
      <EditItemTemplate> 
       <asp:TextBox ID="TextBox1" 
          runat="server" 
          EnableViewState="False" 
          Text='<%# Bind("Title") %>'> 
       </asp:TextBox> 
       <asp:RequiredFieldValidator ID="RequiredFieldValidator4" 
              runat="server" 
              ControlToValidate="TextBox1" 
              Display="Dynamic" 
              ErrorMessage="must enter a title" 
              ValidationGroup="PictureEdit"> 
       </asp:RequiredFieldValidator> 
      </EditItemTemplate> 
      <ItemTemplate> 
       <asp:Label ID="Label1" 
          runat="server" 
          Text='<%# Bind("Title") %>'> 
       </asp:Label> 
      </ItemTemplate> 
     </asp:TemplateField> 
     <asp:TemplateField HeaderText="Description" SortExpression="Description"> 
      <EditItemTemplate> 
       <asp:TextBox ID="TextBox2" 
          runat="server" 
          Columns="25" 
          Rows="4" 
          Text='<%# Bind("Description") %>' 
          TextMode="MultiLine"> 
       </asp:TextBox> 
       <asp:RequiredFieldValidator ID="RequiredFieldValidator5" 
              runat="server" 
              ControlToValidate="TextBox2" 
              Display="Dynamic" 
              ErrorMessage="you must enter a description" 
              ValidationGroup="PictureEdit"> 
       </asp:RequiredFieldValidator>< 
      </EditItemTemplate> 
      <ItemTemplate> 
       <asp:Label ID="Label2" 
          runat="server" 
          Text='<%# Bind("Description") %>'> 
       </asp:Label> 
      </ItemTemplate> 
     </asp:TemplateField> 
     <asp:TemplateField HeaderText="Date Added" SortExpression="UploadedOn"> 
      <EditItemTemplate> 
       <asp:Label ID="Label4" 
          runat="server" 
          Text='<%# Bind("UploadedOn") %>'> 
       </asp:Label> 
      </EditItemTemplate> 
      <ItemTemplate> 
       <asp:Label ID="Label3" 
          runat="server" 
          Text='<%# Bind("UploadedOn") %>'> 
       </asp:Label> 
      </ItemTemplate> 
     </asp:TemplateField> 
     <asp:ImageField DataImageUrlField="PictureID" 
         DataImageUrlFormatString="~/UploadedImages/{0}.jpg" 
         HeaderText="Image" 
         ReadOnly="True"> 
      <ControlStyle Width="100px" /> 
     </asp:ImageField> 
    </Columns> 
    <EditRowStyle BackColor="#2461BF" /> 
    <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> 
    <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> 
    <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" /> 
    <RowStyle BackColor="#EFF3FB" /> 
    <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" /> 
    <SortedAscendingCellStyle BackColor="#F5F7FB" /> 
    <SortedAscendingHeaderStyle BackColor="#6D95E1" /> 
    <SortedDescendingCellStyle BackColor="#E9EBEF" /> 
    <SortedDescendingHeaderStyle BackColor="#4870BE" /> 
</asp:GridView> 

Answer 1

你需要确保你有约束力的PictureReadOnlyCategories DDL来填充项目之前你要绑定所选项目。问题看起来像事情正在进行的顺序，这就是全部。如果您尝试选择不存在的DDL中的项目，则会出现该错误。