Getting the content of an ASP.NET System.Web.UI.WebControls.PlaceHolder

Question

I have a server control that has a PlaceHolder that is an InnerProperty. In the class when rendering I need to get the text / HTML content that is supposed to be in the PlaceHolder. Here is a sample of what the front end code looks like:

<tagPrefix:TagName runat="server">
    <PlaceHolderName>
      Here is some sample text!
    </PlaceHolderName>
</tagPrefix:TagName>

This all works fine except I do not know how to retrieve the content. I do not see any render methods exposed by the PlaceHolder class. Here is the code for the server control.

public class TagName : CompositeControl
{
    [TemplateContainer(typeof(PlaceHolder))]
    [PersistenceMode(PersistenceMode.InnerProperty)]
    public PlaceHolder PlaceHolderName { get; set; }

    protected override void RenderContents(HtmlTextWriter writer)
    {
       // i want to retrieve the contents of the place holder here to 
       // send the output of the custom control.
    }        
}

Any ideas? Thanks in advance.

I've never seen anyone do this before. I would be extremely surprised if it worked at all. What makes you think "this all works"? — John Saunders, Dec 23 '10 at 16:40
Hi John, I just posted the answer to this. To answer your question though any web control should be able to be rendered to its raw HTML output, as far as I know. — Payson Welch, Dec 23 '10 at 16:57

score 4 · Answer 1 · answered Dec 23 '10 at 16:55

4

I just found the solution. I did not see the render methods because of the context of how I was using the PlaceHolder object. Eg I was trying to use it as a value and assign it to a string like so:

string s = this.PlaceHolderName...

Because it was on the right hand side of the equals Intellisense did not show me the render methods. Here is how you render out a PlaceHolder using and HtmlTextWriter:

   StringWriter sw = new StringWriter();
   HtmlTextWriter htw = new HtmlTextWriter(sw);
   this.PlaceHolderName.RenderControl(htw);
   string s = sw.ToString();

answered Dec 23 '10 at 16:55

Payson Welch

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And this gets the content? I'm very surprised. – John Saunders Dec 23 '10 at 16:57
http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.placeholder.rendercontrol.aspx – s_hewitt Dec 23 '10 at 17:00
Would need to see more code, are you manipulating string "s"? Otherwise, why not just pass the writer from RenderContents method to this.PlaceHodlerName.RenderControl, so the contents go straight to the output stream – s_hewitt Dec 23 '10 at 17:11
s_hewitt this is from demonstration only - in my actual control I am outputting the content of PlaceHolder as XML so that I can apply XSL transformations. – Payson Welch Dec 23 '10 at 18:01

score 1 · Accepted Answer · answered Dec 23 '10 at 18:06

Posting this as a second answer so I can use code formatting. Here is an updated method that uses Generics and also uses the 'using' feature to automatically dispose the text / html writers.

    private static string RenderControl<T>(T c) where T : Control, new()
    {
        // get the text for the control
        using (StringWriter sw = new StringWriter())
        using (HtmlTextWriter htw = new HtmlTextWriter(sw))
        {
            c.RenderControl(htw);
            return sw.ToString();
        }
    }

Getting the content of an ASP.NET System.Web.UI.WebControls.PlaceHolder

2 Answers2