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Asked: 2026-05-16T10:54:24+00:00

I have a designer working at the ASPX level. He doesn’t do C#, doesn’t

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I have a designer working at the ASPX level. He doesn’t do C#, doesn’t do code-behinds, doesn’t compile, etc. He’s a pure designer, working with HTML and server controls.

I need a conditional control — an If…Then-ish type thing. Normally, I would do this:

<asp:Placeholder Visible='<%# DateTime.Now.Day == 1 %>' runat="server">
  It's the first day of the month!
</asp:PlaceHolder>

Is there any way to do something like this without the databinding syntax? Something like:

<asp:If test="DateTime.Now.Day == 1" runat="server">
  It's the first day of the month!
</asp:If>

Is there some kind of way to extend a placeholder to allow this? I’ve fiddled around a bit, but in the end, I have a conditional that I essentially have to compile.

Now, there’s nothing wrong with the databinding syntax, but’s just one more bit of…weirdness, the a designer is going to have to understand. Additionally, it doesn’t give me “else” statements. Something like this would be great…

<asp:If test="DateTime.Now.Day == 1" runat="server">
  It's the first day of the month!
  <asp:Else>
    It's not the first day of the month!
  </asp:Else>
</asp:If>
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1 Answer

  1. Editorial Team

    The data-binding syntax has two problems: first it’s a little weirder for your designer vs. using plain text, and second it requires the designer to remember to invert the “if” test in your “else” block.

    The first problem may annoy your designer a little, but the second problem is much more severe, because it forces your designer to think like a programmer (inverting boolean logic!) and makes every if/else block into a possible bug you need to test for after your designer hands over a template.

    My suggestion: use data-binding syntax, but fix the more severe problem by creating custom controls that only require data-binding test code on the If control, but not on the Else control. Sure your designers will have to type a few more characters, but the other more severe problems won’t apply and your performance won’t suffer as it would if you had to dynamically compile code each time your page ran.

    Here’s an example I coded up to illustrate:

    <%@ Page Language="C#"%>
<%@ Register Assembly="ElseTest" TagPrefix="ElseTest" Namespace="ElseTest"%>

<script runat="server">
    protected void Page_Load(object sender, EventArgs e)
    {
        DataBind();
    }
</script>

<html>
<body>

    <ElseTest:IfControl runat="server" visible="<%#1 == 1 %>">
        This should be visible (in "if" area) 
    </ElseTest:IfControl>
    <ElseTest:ElseControl runat="server">
        This should not be visible (in "else" area) 
    </ElseTest:ElseControl>

    <br /><br />

    <ElseTest:IfControl runat="server" visible="<%#0 == 1 %>">
        This should not be visible (in "if" area) 
    </ElseTest:IfControl>
    <ElseTest:ElseControl runat="server">
        This should be visible (in "else" area) 
    </ElseTest:ElseControl>

</body>
</html>

    Here’s the underlying controls, which are simply wrappers around asp:Literal:

    using System;
using System.Web.UI;
using System.Web.UI.WebControls;

[assembly: TagPrefix("ElseTest", "ElseTest")]
namespace ElseTest
{
    // simply renames a literal to allow blocks of data-bound-visibility
    [ToolboxData("<{0}:IfControl runat=\"server\"></{0}:IfControl>")]
    public class IfControl : Literal
    {
    }

    [ToolboxData("<{0}:ElseControl runat=\"server\"></{0}:ElseControl>")]
    public class ElseControl : Literal
    {
        public override bool Visible
        {
            get
            {
                // find previous control (which must be an IfControl). 
                // If it's visible, we're not (and vice versa)
                for (int i = Parent.Controls.IndexOf(this)-1; i >= 0; i--)
                {
                    Control c = Parent.Controls[i];
                    if (c is IfControl)
                        return !c.Visible;  // found it! render children if the if control is not visible
                    else if (c is Literal)
                    {
                        // literals with only whitespace are OK. everything else is an error between if and then
                        Literal l = c as Literal;
                        string s = l.Text.Trim();
                        if (s.Length > 0)
                            throw new ArgumentException("ElseControl must be immediately after an IfControl");
                    }
                }
                throw new ArgumentException("ElseControl must be immediately after an IfControl");
            }
            set
            {
                throw new ArgumentException("Visible property of an ElseControl is read-only");
            }
        }
    }
}

    If you want it more concise, you can easily shorten the tag name (by changing the class names and/or tag prefix). You can also create a new property (e.g. “test”) to use instead of “Visible”.

    If you really want to get rid of the <%# %>, there are likley many different tricks you can use to leverage CodeDOM or other ways to dynamically compile code, although performance will be a challenge since you’ll probably end up dynamically compiling code each time the page runs, it may introduce pesky security issues, and more. I’d stay away from that.

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