ASP.NET: Wrong event is fired when I click a LinkButton

Question

I have a "cart" Repeater, where every item has a couple of controls in it. The ones we're focusing on are two DropDownLists, a LinkButton and a TextBox. The lists are on one validation group and the button & textbox are on another.

Both lists have an OnSelectedIndexChanged event handler which does some calculations based on the selections in both DropDownLists. Both lists also have AutoPostBack="True".

The button has an OnClick handler which also does some calculations according to the number in the textbox.

I need the calculations to be updated immediately - so I added another data binding for the Repeater - on each event handler

The problem is - I can't get the value from the TextBox after I click on one of the DropDownLists. It always comes off as 1. In the background, the OnSelectedIndexChanged event handler fires first, and the buttons' OnClick will fires after it. That only happens after I change one of the lists - and it happens every time I click that button from that moment on. Before that - everything is normal on all controls.

What do you think? Below is some code (I hope it's not too much, I included everything that's taking part) - Thank you very much!

Here's the repeater template:

                <ItemTemplate>
                    <tr>
                        <td class="size"><div><asp:DropDownList runat="server" ID="_selectSize" AutoPostBack="true" OnSelectedIndexChanged="selectChange" EnableViewState="true" TabIndex="<%#Container.ItemIndex%>" ValidationGroup="doNotValidate"></asp:DropDownList></div></td>
                        <td class="material"><div><asp:DropDownList runat="server" ID="_selectMaterial" AutoPostBack="true" OnSelectedIndexChanged="selectChange" EnableViewState="true" TabIndex="<%#Container.ItemIndex%>" ValidationGroup="doNotValidate"></asp:DropDownList></div></td>
                        <td class="quantity">
                            <div>
                                <div class="quantity_container"><asp:TextBox runat="server" ID="_txtAmount" name="quantity_<%#Container.ItemIndex%>" ValidationGroup="vCart"></asp:TextBox></div>
                                <div><asp:LinkButton runat="server" CssClass="refresh" id="_refreshCart" ValidationGroup="vCart"></asp:LinkButton></div>
                            </div>
                        </td>
                    </tr>
                </ItemTemplate>

The Repeater.DataBound():

Protected Sub rptCart_ItemDataBound(sender As Object, e As System.Web.UI.WebControls.RepeaterItemEventArgs) Handles rptCart.ItemDataBound
    If e.Item.ItemType = ListItemType.AlternatingItem OrElse e.Item.ItemType = ListItemType.Item Then
        Dim OrderItem As ProxyMarket.Item = CType(e.Item.DataItem, ProxyMarket.Item)
        Dim btnRemoveProduct As LinkButton = CType(e.Item.FindControl("_removeProduct"), LinkButton)
        Dim btnRefreshCart As LinkButton = CType(e.Item.FindControl("_refreshCart"), LinkButton)
        Dim txtAmount As TextBox = CType(e.Item.FindControl("_txtAmount"), TextBox)
        Dim sizeSelect As DropDownList = CType(e.Item.FindControl("_selectSize"), DropDownList)
        Dim materialSelect As DropDownList = CType(e.Item.FindControl("_selectMaterial"), DropDownList)

        btnRemoveProduct.CommandName = OrderItem.ID
        btnRefreshCart.CommandName = OrderItem.ID
        txtAmount.Text = OrderItem.Units

        AddHandler btnRemoveProduct.Click, AddressOf removeProduct
        AddHandler btnRefreshCart.Click, AddressOf refreshCart

        sizeSelect.DataSource = sizeList
        sizeSelect.DataBind()
        sizeSelect.SelectedIndex = s
        materialSelect.DataSource = materialList
        materialSelect.DataBind()
        materialSelect.SelectedIndex = m
    End If
End Sub

Here is the DropDownLists event handler:

Protected Sub selectChange(ByVal sender As DropDownList, ByVal e As System.EventArgs)
    Dim listing As New PriceListing
    Dim ddl As DropDownList
    Dim selectedIndex As Integer

    If sender.ID = "_selectSize" Then
        For Each rptrItem As RepeaterItem In rptCart.Items
            ddl = CType(rptrItem.FindControl("_selectMaterial"), DropDownList)
            If ddl.TabIndex = sender.TabIndex Then Exit For
        Next

        For Each listing In artDecoPricing
            If listing.Size = sender.SelectedValue Then Exit For
        Next

        selectedIndex = ddl.SelectedIndex
        s = sender.SelectedIndex
    ElseIf sender.ID = "_selectMaterial" Then
        For Each rptrItem As RepeaterItem In rptCart.Items
            ddl = CType(rptrItem.FindControl("_selectSize"), DropDownList)
            If ddl.TabIndex = sender.TabIndex Then Exit For
        Next

        For Each listing In artDecoPricing
            If listing.Size = ddl.SelectedValue Then Exit For
        Next

        selectedIndex = sender.SelectedIndex
        s = ddl.SelectedIndex
    End If

    Select Case selectedIndex
        Case 0
            Cart.Order.Items(sender.TabIndex).PriceUnit = listing.Canvas
        Case 1
            Cart.Order.Items(sender.TabIndex).PriceUnit = listing.Acrylic
        Case 2
            Cart.Order.Items(sender.TabIndex).PriceUnit = listing.Framed
        Case 3
            Cart.Order.Items(sender.TabIndex).PriceUnit = listing.Alucobond
    End Select

    Cart.SaveOrder()

    s = sender.SelectedIndex
    m = selectedIndex

    rptCart.DataSource = Cart.Order.Items
    rptCart.DataBind()
End Sub

And finally, the LinkButton OnClick handler:

Protected Sub refreshCart(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim btnRefreshCart As LinkButton = CType(sender, LinkButton)
    Dim amountStr As String
    Dim amount As Integer

    amountStr = CType(btnRefreshCart.Parent.FindControl("_txtAmount"), TextBox).Text
    If IsNumeric(amountStr) Then
        amount = CDbl(amountStr)
    Else
        amount = -1
    End If
    amount = IIf(amount > 0, amount, -30)

    For Each Item As ProxyMarket.Item In Cart.Order.Items
        If Item.ID = btnRefreshCart.CommandName Then
            Item.Units = amount
            Cart.Edit_Product(btnRefreshCart.CommandName, amount)
            Exit For
        End If
    Next

    rptCart.DataSource = Cart.Order.Items
    rptCart.DataBind()
End Sub

Thank you :)

Answer 1

I found a solution!

Apparently this is happening because of a viewstate limitation in ASP.NET which causes the OnSelectedIndexChanged to fire on Page_Load regardless if the user actually selected a different value.

So when the event handler fires, I am checking whether it is the DropDownLists which called me or a different control - that prevents the event from firing when it doesn't need to - and keeps all event handling on the page intact:

Protected Sub selectChange(ByVal sender As DropDownList, ByVal e As System.EventArgs)
    Dim senderClientID = Page.Request.Params.Get("__EVENTTARGET")
    ' Run ONLY if the relevant select control was clicked,
    ' otherwise this is only fired because of ASP.NET limitations,
    ' and will screw up the original event:
    If senderClientID.IndexOf("_selectSize") <> -1 Or senderClientID.IndexOf("_selectMaterial") <> -1 Then
        'do stuff