How do I get the HTML output of a UserControl in .NET (C#)?

Question

If I create a UserControl and add some objects to it, how can I grab the HTML it would render?

ex.

UserControl myControl = new UserControl();
myContr         


        

Answer 1

You could utilize the HttpServerUtility.Execute Method, available through HttpContext.Current.Server.Execute:

var page = new Page();
var myControl = (MyControl)page.LoadControl("mycontrol.ascx");
myControl.SetSomeProperty = true;
page.Controls.Add(myControl);
var sw = new StringWriter();
HttpContext.Current.Server.Execute(page, sw, preserveForm: false);

The benefit would be that you also trigger the Page_Load event of your user control.

MSDN documentation can be found here: https://msdn.microsoft.com/en-us/library/fb04e8f7(v=vs.110).aspx.

Answer 2

UserControl uc = new UserControl();
MyCustomUserControl mu = (MyCustomUserControl)uc.LoadControl("~/Controls/MyCustomUserControl.ascx");

TextWriter tw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(tw);

mu.RenderControl(hw);

return tw.ToString();

Answer 3

Call its .RenderControl() method.

Answer 4

You can render the control using Control.RenderControl(HtmlTextWriter).

Feed StringWriter to the HtmlTextWriter.

Feed StringBuilder to the StringWriter.

Your generated string will be inside the StringBuilder object.

Here's a code example for this solution:

string html = String.Empty;
using (TextWriter myTextWriter = new StringWriter(new StringBuilder()))
{
    using (HtmlTextWriter myWriter = new HtmlTextWriter(myTextWriter))
    {
        myControl.RenderControl(myWriter);
        html = myTextWriter.ToString();
    }
}

Answer 5

Seven years late, but this deserves to be shared.

The generally accepted solution - StringBuilder into StringWriter into HtmlWriter into RenderControl - is good. But there are some gotchas, which I unfortunately ran across while trying to do the same thing. Some controls will throw errors if they're not inside of a Page, and some will throw errors if they're not inside of a <form> with runat="server". The ScriptManager control exhibits both of these behaviours.

I eventually found a workaround here. The gist of it is basically just instantiating a new Page and Form before doing the writer work:

Page page = new Page();
page.EnableEventValidation = false;

HtmlForm form = new HtmlForm();
form.Name = "form1";
page.Controls.Add(form1);

MyControl mc = new MyControl();
form.Controls.Add(mc);

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
HtmlTextWriter writer = new HtmlTextWriter(sw);

page.RenderControl(writer);

return sb.ToString();

Unfortunately, this gives you more markup than you actually need (since it includes the dummy form). And the ScriptManager will still fail for some arcane reason I haven't puzzled out yet. Honestly, it's a whole lot of trouble and not worth doing; the whole point of generating controls in the code-behind is so that you don't have to fiddle around with the markup, after all.

Answer 6

//render control to string
StringBuilder b = new StringBuilder();
HtmlTextWriter h = new HtmlTextWriter(new StringWriter(b));
this.LoadControl("~/path_to_control.ascx").RenderControl(h);
string controlAsString = b.ToString();