Self closing Html Generic Control?

I am writing a bit of code to add a link tag to the head tag in the code behind... i.e.

HtmlGenericControl css = new HtmlGenericControl("link");

css.Attributes["rel"] = "Stylesheet&开发者_如何学JAVAquot;;
css.Attributes["type"] = "text/css";
css.Attributes["href"] = String.Format("/Assets/CSS/{0}", cssFile);

to try and achieve something like...

<link rel="Stylesheet" type="text/css" href="/CSS/Blah.css" />

I am using the HtmlGenericControl to achieve this... the issue I am having is that the control ultimatly gets rendered as...

<link rel="Stylesheet" type="text/css" href="/CSS/Blah.css"></link>

I cant seem to find what I am missing to not render the additional </link>, I assumed it should be a property on the object.

Am I missing something or is this just not possible with this control?

I think you'd have to derive from HtmlGenericControl, and override the Render method.

You'll then be able to write out the "/>" yourself (or you can use HtmlTextWriter's SelfClosingTagEnd constant).

Edit: Here's an example (in VB)

While trying to write a workaround for umbraco.library:RegisterStyleSheetFile(string key, string url) I ended up with the same question as the OP and found the following.

According to the specs, the link tag is a void element. It cannot have any content, but can be self closing. The W3C validator did not validate <link></link> as correct html5.

Apparently

HtmlGenericControl css = new HtmlGenericControl("link");

is rendered by default as <link></link>. Using the specific control for the link tag solved my problem:

HtmlLink css = new HtmlLink();

It produces the mark-up <link/> which was validated as correct xhtml and html5.

In addition to link, System.Web.UI.HtmlControls contains classes for other void element controls, such as img, input and meta.

Alternatively you can use Page.ParseControl(string), which gives you a control with the same contents as the string you pass.

I'm actually doing this exact same thing in my current project. Of course it requires a reference to the current page, (the handler), but that shouldn't pose any problems.

The only caveat in this method, as I see it, is that you don't get any "OO"-approach for creating your control (eg. control.Attributes.Add("href", theValue") etc.)

I just created a solution for this, based on Ragaraths comments in another forum:

http://forums.asp.net/p/1537143/3737667.aspx

Override the HtmlGenericControl with this

protected override void Render(HtmlTextWriter writer)
{
    if (this.Controls.Count > 0)
        base.Render(writer); // render in normal way
    else
    {
        writer.Write(HtmlTextWriter.TagLeftChar + this.TagName); // render opening tag
        Attributes.Render(writer); // Add the attributes.  
        writer.Write(HtmlTextWriter.SelfClosingTagEnd); // render closing tag   
    }

    writer.Write(Environment.NewLine); // make it one per line
}

The slightly hacky way.

• Put the control inside a PlaceHolder element.
• In the code behind hijack the render method of the PlaceHolder.
• Render the PlaceHolders content exactly as you wish.

This is page / control specific and does not require any overrides. So it has minimal impact on the rest of your system.

<asp:PlaceHolder ID="myPlaceHolder" runat="server">
    <hr id="someElement" runat="server" />
</asp:PlaceHolder>

protected void Page_Init(object sender, EventArgs e)
{
    myPlaceHolder.SetRenderMethodDelegate(ClosingRenderMethod);
}

protected void ClosingRenderMethod(HtmlTextWriter output, Control container)
{
    var voidTags = new HashSet<string>(StringComparer.InvariantCultureIgnoreCase) { "br", "hr", "link", "img" };
    foreach (Control child in container.Controls)
    {
        var generic = child as HtmlGenericControl;
        if (generic != null && voidTags.Contains(generic.TagName))
        {                
            output.WriteBeginTag(generic.TagName);
            output.WriteAttribute("id", generic.ClientID);
            generic.Attributes.Render(output);
            output.Write(HtmlTextWriter.SelfClosingTagEnd);                
        }
        else
        {
            child.RenderControl(output);
        }
    }
}