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Emailing Rendered Output Fails in ASP.NET 2.0

Posted on 2008-11-12
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Last Modified: 2013-11-07
I am trying to email an entire page of controls in HTML format.  This worked flawlessly in 1.1, but after upgrading to 2.0 the rendercontrol command crashes with a "RegisterforEventValidation can only be called during Render().  The HTML side consists of a form that contains the panel "wholeform", and all objects on the page are enclosed in that.

I have already tried setting enableeventvalidation = false in the page directive, and experimenting
with the visibility property of different objects with no success.

Any help would be greatly appreciated.  Please be explicit, since I'm no expert.  Thanks.

Dim p As New Page       		'Create a new Page instance and a server-side form
        Dim hf As New HtmlForm
 
        p.Controls.Add(hf)  		'Build up the control hierarchy
        hf.Controls.Add(wholeform)
 
        Dim SB As New StringBuilder
        Dim SW As New StringWriter(SB)
        Dim htmlTW As New HtmlTextWriter(SW)
 
        p.DesignerInitialize()
        p.RenderControl(htmlTW)     'Call the page's RenderControl() method
 
        p = Nothing
 
       strEmailBody = SB.ToString()
 
	... code to email

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Question by:KarenH1
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by:NazoUK
NazoUK earned 1000 total points
ID: 22948681
There's an article over at 4 guys from Rolla that describes this problem:

http://aspnet.4guysfromrolla.com/articles/122006-1.aspx

I think the fact that you are trying to use a page variable will cause additional problems though because that will have its own render event, event validation etc. This is why disabling event validition isn't working in your case. I recommend using rendercontrol of wholeform directly instead of using the page variable. If you need additional html adding to the rendered output it should be trivial to do this as strings.
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Accepted Solution

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KarenH1 earned 0 total points
ID: 22978973
NazoUK - Thank you for your reply.  I got the original code from 4 guys from Rolla, and tried all their workarounds.  They admit this code breaks in 2.0.  I do believe I tried to do a renderconrol of the wholeform with the same results.

I think I have a solution:

Dim sbNewOne As New StringBuilder()
            Dim mywriter As New HtmlTextWriter(New System.IO.StringWriter(sbNewOne))
            ' Without this, get "a page can only have one server side form tag"
            MyBase.Visible = False
            MyBase.Render(mywriter)

            Response.Write(sbNewOne.ToString())
            strEmailBody = sbNewOne.ToString()

This seems to work no problem.
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