Question

I have an UpdatePanel with a DropDownList. Within the UpdatePanel I am adding some custom controls to a PlaceHolder which have a button in with OnClick="AddItemToCart". If I refresh my page and press the button the AddItemToCart event is called, if I change the DropDownList to something other than the default value loaded with the page then the AddItemToCart event doesn’t fire. I am able to change the DropDownList back to the default value and it will allow the event to trigger again.

I assume this is something to do with event registration but I am not sure where to look. I have tried programatically assigning the OnClick value to the button on each postback but that doesn’t seem to work. I don’t understand what is going wrong because the postback is working, my event however is not triggered.

To summarise, my OnClick doesn’t fire after the ajax postback IF the dropdown value differs from the value it loaded on the page load.

This is my code (although I am not sure it will help):

<asp:UpdatePanel ID="updSIListCnt" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <asp:DropDownList id="ddlSort" runat="server" OnSelectedIndexChanged="ApplyFilters" AutoPostBack="True" Width="23%">
            <asp:ListItem Value="0">Sort By Relevancy</asp:listitem>
            <asp:ListItem Value="1">Sort By Product Code</asp:listitem>
            <asp:ListItem Value="2">Sort By Product Description</asp:listitem>
            <asp:ListItem Value="3">Sort By Price - Lowest</asp:listitem>
            <asp:ListItem Value="4">Sort By Price - Highest</asp:listitem>
        </asp:DropDownList>

        <asp:PlaceHolder id="phContentListCnt" runat="server" />
    </ContentTemplate>
</asp:UpdatePanel>
<asp:UpdateProgress ID="upSIList" runat="server" AssociatedUpdatePanelID="updSIListCnt">
    <ProgressTemplate>
        <asp:Image id="imgLoading" runat="server" ImageUrl="~/Images/loading.gif" CssClass="loader" />
    </ProgressTemplate>
</asp:UpdateProgress>

phContentListCnt contains several instances of:

 <asp:ImageButton ID="btnAddToBasket" runat="server" ImageUrl="~/Images/Buttons/add_to_basket.jpg" OnClick="AddItemToCart" CausesValidation="false" />

ApplyFilters runs some SQL and calls UpdatePanel.Refresh()

Answer 1

I managed to find the cause of this problem.

In ApplyFilters I was reloading the controls and adding them to phContentListCnt but I was clearing the place holder first. This meant that the events registered in Page_Load were cleared as well and it was to late in the page life cycle at this point to register the new events. On this note, I am checking my filters in page load using Request.Form[] so I can load my dynamic controls in the page load.