RenderControl in HtmlTextWriter - InvalidOperationException

Question

I would like to render a Control object which is just created on the fly when the user send a postback request. To do so, I use the code below:

StringBuilder sb = new StringBuilder();
HtmlTextWriter ht = new HtmlTextWriter(new StringWriter(sb));
Rating r = new Rating("r", 5, 3, No, Big);
r.RenderControl(ht);

which unfortunately yields to an InvalidOperationException at the last line and with the following error:

The page can not be null. Make sure that this operation is performed in the context of an ASP.NET request.

I probably misunderstood the way I should use this RenderControl method, and I hope you can help me with my problem.

Thank you, David

Answer 1

It doesn't look like you're attaching your new Rating control to your Page control before attempting to render it.

From the MSDN docs for RenderControl , the internals of the call are going to be looking for the enclosing Page, and performing some activities based on the Page object's settings.

You might add a placeholder in your page and insert the Rating control there before attempting to render it.