Inline Code on Webform Property

Question

Why doesn't this display the date/time when rendered?

<asp:Label runat="server" ID="test" Text="<%= DateTime.Now.ToString() %>" ></asp:Label>

Is there anyway to make this work?

Answer 1

Well the asp tags are rendered. You will have to set the property at runtime. or just do the <%= DateTime.Now.ToString() %>.

Answer 2

Asp.net server controls don't play well with the <%=, instead you can do:

<span><%= DateTime.Now.ToString() %></span>

Ps. you could alternatively set the label's text on the code-behind. It might work for your scenario to set it on the PreRenderComplete.

Answer 3

The real problem here though is I need to set the property of a WebControl with code on the markup page. The only way I've found to do this is put the whole control in a code block. Its not elegant or suggested but when all else fails this will work.

 <%
  var stringBuilder = new StringBuilder();
  var stringWriter = new StringWriter(stringBuilder);
  var htmlWriter = new HtmlTextWriter(stringWriter);
  var label = new Label { Text = DateTime.Now.ToString() };
  label.RenderControl(htmlWriter);
  Response.Write(stringBuilder.ToString());
  %>

But this won't work if you need the control to maintain state.

UPDATE:

After researching Kev's answer I did find an even better solution. I don't have a code behind (its an MVC page) but you can still reference a control on the page through a code block so my new solution is the following. Note - You have to place the code block first for this to work.

 <%
    lblTest.Text = DateTime.Now.ToString();
 %>
<asp:label runat="server" ID="lblTest" />

Thanks for the inspiration Kev!

Answer 4

I'm not sure if you've got a code behind file, but if you really need to set the label's Text property in the .aspx markup you could add the following code to the page:

<script runat="server">
    protected override void OnPreLoad(EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            this.test.Text = DateTime.Now.ToString();
            base.OnPreLoad(e);
        }
    }
</script>

This way you can maintain the label control's state on postback.

HTH
Kev

Answer 5

The simplest way to make that work would be to use a data-binding expression in place of the code render block...

<asp:Label runat="server" ID="test" Text="<%# DateTime.Now.ToString() %>" ></asp:Label>

Now the Text property will be set whenever Page.DataBind() is called, so in your code-behind you'll want something like

protected override void OnPreRender(EventArgs e)
{
    if (!Page.IsPostBack)
    {
        DataBind();
    }

   base.OnPreRender(e);
}