Question

below is my listview code example, while the products are populating, I want to check every single one of them against my database whether it’s quantity is 0, how can add a method in code behind to do this:

I tried doing this under the onselectedindexchanged event but got the ‘Object reference not set to an instance of an object.’ exception :

Appreciate any help given. Thanks!

         using (XXXShop db = new XXXShop ())
        {
             var availability = from p in db.Products
                                where p.Quantity == 0
                                select p;

        (ListView_Products.FindControl("litStatus") as Literal).Text = "Unavailable";
        }         

ListView code:

    <asp:ListView ID="ListView_Products" runat="server" DataKeyNames="ProductID"  
    DataSourceID="EDS_ProductsByCategory" GroupItemCount="3" 
    onselectedindexchanged="Page_Load">
   <EmptyDataTemplate><table runat="server"><tr><td>No data was returned.</td></tr></table></EmptyDataTemplate>
    <EmptyItemTemplate><td runat="server" /></EmptyItemTemplate>
    <GroupTemplate><tr ID="itemPlaceholderContainer" runat="server"><td ID="itemPlaceholder" runat="server"></td></tr></GroupTemplate>
    <ItemTemplate>
        <td runat="server">
            <table border="0" width="295">
              <%-- Product pics --%>
                <tr>        
                    <td style="vertical-align: middle; text-align: center;">
                        <a href='ProductDetails.aspx?productID=<%# Eval("ProductID") %>'>
                            <image src='Catalog/Images/Thumbs/<%# Eval("ProductImage") %>' width="195" height="270" border="0">
                        </a>
                    </td>
                </tr>
                <tr>
                    <%-- Product info, description, price...etc --%>
                     <td style="width: 250px; vertical-align: middle; text-align: center; padding-bottom: 5px;">                          
                     <b>Price: </b><%# Eval("UnitCost", "{0:c}")%>                 
                    </td>                                       
                </tr>
                <tr>
                     <td style="width: 250px; vertical-align: middle; text-align: center; padding-bottom: 25px;">
                         <asp:Literal ID="litStatus" runat="server" />
                     </td>
                </tr>                               
              </table>

        </td>
    </ItemTemplate>
    <LayoutTemplate>
        <table runat="server">
            <tr runat="server">
                <td runat="server">
                    <table ID="groupPlaceholderContainer" runat="server">
                        <tr ID="groupPlaceholder" runat="server"></tr>
                    </table>
                </td>
            </tr>
            <tr runat="server"><td runat="server"></td></tr>
        </table>
    </LayoutTemplate>
</asp:ListView>

Answer 1

I haven’t done that much with ASP.NET or used the ListView so i don’t know if there might be better ways to do this, but you could add a method to your codebehind that can format your data the way you want. Like the following:

protected string FormattedQuantity(int quantity)
{
  return quantity > 0 ? quantity.ToString() : "Unavailable";
}

You should then be able to use this formatter anywhere in your aspx file by doing the following:

<asp:Label ID="OccurrenceLabel" runat="server" 
  Text='<%# FormattedQuantity((int)Eval("Quantity")) %>' />