Problem with conditional statements in asp.net

Question

I'm trying to do the following in a aspx page:

<%@ Page Language="C#" EnableSessionSTate="true" ValidateRequest="False" Inherits="MyProject.CodeBehind.MYWF.SiteWF" MasterPageFile="~/_layouts/application.master" %>
<asp:Content ID="Content5" ContentPlaceHolderID="PlaceHolderPageDescription" runat="server">
    <% if (!isOld) %>
    <% { %>
        <p>display this</p>
    <% } %>

</asp:Content>

isOld is a public bool variable from the cs file mentioned in the namespace.

But unfortunately it gave me an unknown error.

I could do something similar in JSPs, but after googling around for a while, I'm not so sure whether the above is achievable in ASP.NET? (Am I missing a tag declaration, or do I have to write the entire tag lib myself?)

Thanks.

EDIT: I just got an unknown error. I have a feeling that the code above has either the wrong syntax or are totally off the wrong track. I tried the following code, and there was no error, but the bool variable is always false:

<% #if !isOld %>
    <p> display this</p>
<% #endif %>

And what error was it? Something like: "Cannot modify the controls collection"? If so, then you're just out of luck. You need to stop the code that is modiying the controls (by adding or removing one, somewhere in your codebehind) or make the 'display this' appear in a PlaceHolder and set it's Visible property appropriately (this is what I would do). — Noon Silk
– Noon Silk, Commented Mar 2, 2010 at 7:59
Re: your edit, you're missing a bracket: <% if (!isOld) %> should be <% if (!isOld) { %> (note bracket). (Edit: actually, perhaps not, I've never seen anyone write the bracket in a totally different <% %> area though, it seems odd .. — Noon Silk
– Noon Silk, Commented Mar 2, 2010 at 8:10

AndreasKnudsen · Accepted Answer · 2010-03-02 08:06:21Z

3

in your code front:

<%@ Page Language="C#" EnableSessionSTate="true" ValidateRequest="False" Inherits="MyProject.CodeBehind.MYWF.SiteWF" MasterPageFile="~/_layouts/application.master" %>
<asp:Content ID="Content5" ContentPlaceHolderID="PlaceHolderPageDescription" runat="server">
    <asp:PlaceHolder runat="server" id="PlaceHolderIsOld">
        <p>display this</p>
    </asp:PlaceHolder>
</asp:Content>

and then in your code behind:

protected void Page_Load(object sender, EventArgs e){
   PlaceHolderIsOld.Visible = IsOld;
}

answered Mar 2, 2010 at 8:06

AndreasKnudsen

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3 Comments

BeraCim Over a year ago

@AndreasKnudsen: where does PlaceHolderIsOld live in the code behind? My code behind inherits System.Web.UI.Page and I do not have a Page_Load method. I can't seem to access PlaceHolderIsOld in anyway.

AndreasKnudsen Over a year ago

By defining the placeholder in your codefront it will automatically appear as useable in your codebehind. (Visual studio generates the code in the *.designer.cs file) Asp.Net is hard-wired to look for certain methods in pages and user controls using reflection. if you define a method with the signature as presented in the code above then Asp.Net will call it at the "Load" part of the page lifecycle. though mildly cryptic especially for advanced sites using nested controls and masterpages it's well worth learning: coolwebdeveloper.com/downloads/ASPNET20PageLifeCycle.jpg

BeraCim Over a year ago

What I ended up doing was something similar to your code above: setting everything on the server side. I made the item/content area visible when certain conditions were met etc instead of using asp syntax. Worked just as well. Thanks for the idea and also the diagram too.

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