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Why am I getting errors viewing my ASP.Net user controls in the Visual Studio Designer?

Posted on 2014-10-16
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Last Modified: 2014-10-29
Hi:

I'm working with ASP.Net in Visual Studio 2010.
I've created several user controls which I include in .aspx pages.
They work fine at runtime, however I run into issues when I am in
"Design" view in Visual Studio.

I've added the following to my web.config:

    <pages>
      <controls>
        <add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />
        <add src="~/UserControls/UserControl1.ascx" namespace="" tagName="QuantityManagerUserControl" tagPrefix="ucUserControl1" />
        <add src="~/UserControls/UserControl2.ascx"  namespace="" tagName="PopupUserControl" tagPrefix="ucUserControl2" />
      </controls>
    </pages>

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The user controls are included directly as part of the current solution.
I do not have name spaces defined for the controls.

Things are fine when I am in "Source View" of the designer.
But, when I go into design view. The controls do not render.
I get the following error message:
Error Rendering Control - UserControl1
An unhandled exception has occurred.
The 'namespace' attribute cannot be an empty string.

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I've tried adding namespaces to the controls, removing the namespace tag from the web.config file.
I still get the same errors.

What am I missing here?
What do I need to do additionally in order to view the controls in the Visual Studio designer?

Thanks,
JohnB
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Question by:jxbma
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Expert Comment

by:CodeCruiser
Comment Utility
Try adding namespace in lines
<add src="~/UserControls/UserControl1.ascx" namespace="" tagName="QuantityManagerUserControl" tagPrefix="ucUserControl1" />

and use the project name as the namespace.
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Author Comment

by:jxbma
Comment Utility
::>CodeCruiser:

I try adding the project as my namespace in the web config.
Doing so caused additional errors when I looked at page in design view.

It should be noted that I don't have an explicit namespace in my user controls.
I tried adding a namespace there and then referencing that namespace in the web.config and I got the
same errors in design view mentioned above.

Is it possible to provide/point me to a sample that actually works.

Thanks,
JB
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Accepted Solution

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jxbma earned 0 total points
Comment Utility
OK. I finally figured this out.

If you have any user control definitions in the <pages><controls> section in your web config which contain a
namespace="" attribute, then it seems that Visual Studio (2010) will choke on displaying any of the
user controls defined in that section in the designer.

All you need is to have 1 entry in order for this to occur. It doesn't matter that the definition of the embedded control
that you are trying to view does not contain the 'namespace=""' attribute.

JB
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Author Closing Comment

by:jxbma
Comment Utility
Nobody responded to answering this. I was able to figure it out on my own.
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