Question

Why am I getting a Runtime error when trying to pre-select a value from a DropDownList in ASP.net 2.0 vb?

I’ve tried to do the same thing with a GridView and I get the same message.

Initially I’m trying to show the user the details they submitted to apply for access. When clicking the edit button, I want to allow the user to alter the details they submitted to us and update the application. I’m not looking to do any additional inserting into the database.

I wanted to restrict the user to selecting the department from a DropDownList. When the user clicks edit, I want the department they originally applied with to be pre-selected. When I have the line:

SelectedValue='<%# Bind("department") %>'

I get a Runtime error. If I remove the line, it doesn’t error but doesn’t pre-select anything.

Is anyone able to help me understand why its not working?

Something else that might help is that I’m using Visual Studio 2005 and as I type class properties are being shown as I type. I can see lots of properties for the DropDownList when I press my spacebar, but SelectedValue isn’t one of them which makes me think I’m trying to do something which isn’t supposed to work.

My Code:

<asp:SqlDataSource ID="UserDetails_Conn" runat="server" 
    ConnectionString="<%$ ConnectionStrings:NormCon %>" 
    SelectCommand="SELECT u.first_name, u.last_name, u.email, d.department FROM mis_userlist AS u INNER JOIN mis_depts AS d ON u.dept_id = d.dept_id WHERE (u.windows_login = @windows_ID)"
    UpdateCommand="UPDATE mis_userlist SET first_name = @first_name, last_name = @last_name, email = @email, dept_id = @dept_id WHERE (windows_login = @windows_ID)"
>
    <SelectParameters>
        <asp:SessionParameter Name="windows_ID" SessionField="username" />
    </SelectParameters>
    <UpdateParameters>
        <asp:Parameter Name="first_name" />
        <asp:Parameter Name="last_name" />
        <asp:Parameter Name="email" />
        <asp:Parameter Name="dept_id" />
        <asp:Parameter Name="windows_ID" />
    </UpdateParameters>

</asp:SqlDataSource>
<asp:DetailsView ID="UserDetailsView" runat="server" Height="50px" Width="125px" AutoGenerateRows="False" DataSourceID="UserDetails_Conn">
    <Fields>
        <asp:BoundField DataField="first_name" HeaderText="first_name" SortExpression="first_name" />
        <asp:BoundField DataField="last_name" HeaderText="last_name" SortExpression="last_name" />
        <asp:BoundField DataField="email" HeaderText="email" SortExpression="email" />
        <asp:TemplateField HeaderText="department" SortExpression="department">
            <EditItemTemplate>
                <asp:SqlDataSource ID="DepartmentList" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:NormCon %>" 
                    SelectCommand="SELECT dept_id, department FROM mis_depts ORDER BY department"
                >
                </asp:SqlDataSource>
                <asp:DropDownList ID="ddlDepartments" runat="server"
                    DataSourceId="DepartmentList"
                    DataTextField="department"
                    DataValueField="dept_id"
                    SelectedValue='<%# Bind("department") %>' > <!-- Errorsome line -->
                </asp:DropDownList>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("department") %>'></asp:TextBox>
            </InsertItemTemplate>
            <ItemTemplate>
                <asp:Label ID="Label1" runat="server" Text='<%# Bind("department") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:CommandField ShowEditButton="True" />
    </Fields>
</asp:DetailsView>

Solution

Along with Win’s Solution, I needed to add the dept_id field in the SQL string.

SelectCommand="SELECT u.first_name, u.last_name, u.email, d.department, d.dept_id FROM mis_userlist AS u INNER JOIN mis_depts AS d ON u.dept_id = d.dept_id WHERE (u.windows_login = @windows_ID)"

This allowed department when represented here:
ddlDepartments.SelectedValue = department
to be a value that could link with my DataValueField=”dept_id” line from the DropDownList.

Thanks to Win.

Answer 1

SelectedValue will throw an exception if you assign a value which doesn’t exists in the list.

In order to avoid that, you can validate in DataBound –

Remove SelectedValue='<%# Bind("department") %>' from aspx page, and attach data bound event to UserDetailsView <asp:DetailsView ... OnDataBound="DetailsView_DataBound" ...

Protected Sub DetailsView_DataBound(sender As Object, e As EventArgs)
   Dim detailsView = DirectCast(sender, DetailsView)

   Dim dr = DirectCast(detailsView.DataItem, DataRowView)
   Dim department = dr(4).ToString() ' Column index of department
   *** OR *** Dim department = dr("department").ToString() ' Column by name
   Dim ddlDepartments = TryCast(detailsView.
      FindControl("ddlDepartments"), DropDownList)

   If ddlDepartments IsNot Nothing AndAlso 
      ddlDepartments.Items.FindByValue(department) IsNot Nothing Then
      ddlDepartments.SelectedValue = department
   End If
End Sub

Basically, you are intercepting data binding of controls.

Updated: checking the index of department column.