Can't convert extension node instance to appropriate interface

[Andy Selvig]

Hi-

I have an application using Mono.Addins but I'm having trouble
creating instances of the extension points. The addin itself is being
detected and loading fine, but when I try to create an instance from
an extension node, I get an exception stating that I can't perform the
conversion. I've pasted the relevant code below.

From host addin file:

  <ExtensionPoint path = "/Stems/Petals">
    <ExtensionNode name="Petal" type="Mono.Addins.TypeExtensionNode"/>
  </ExtensionPoint>

from extension addin file:

  <Extension path = "/Stems/Petals">
    <Petal id="RichContent"
type="Swivel.Stems.Controllers.RichContentController" />
  </Extension>

from the host dll:

namespace Swivel.Stems.Controllers
{

        /// <summary>
        /// Interface for petals.
        /// </summary>
        public interface IPetal
        {
            ...
        }
}

from the addin dll:

namespace Swivel.Stems.Controllers
{
    public class RichContentController : Controller, IPetal
    {
    }
}

and from the code that loads the extensions in the host dll:

foreach (TypeExtensionNode node in AddinManager.GetExtensionNodes("/
Stems/Petals"))
{
        IPetal petal = (IPetal)node.CreateInstance();
}

It throws an exception on the CreateInstance call:

Unable to cast object of type
'Swivel.Stems.Controllers.RichContentController' to type
'Swivel.Stems.Controllers.IPetal'.

It seems like this cast is perfectly reasonable. I don't understand
what's going wrong. In the examples on the site, the extensions only
implement the interface, and don't subclass anything else. Is this not
something that's supported?

Thanks.

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[Lluis Sanchez-2]

The most probable cause of the error is that you have several copies of
the host assembly in different locations. .NET considers that types
coming from different assembly locations are different.

El dg 11 de 10 de 2009 a les 11:19 -0700, en/na Andy Selvig va escriure:

> Hi-
>
> I have an application using Mono.Addins but I'm having trouble
> creating instances of the extension points. The addin itself is being
> detected and loading fine, but when I try to create an instance from
> an extension node, I get an exception stating that I can't perform the
> conversion. I've pasted the relevant code below.
>
> >From host addin file:
>
>   <ExtensionPoint path = "/Stems/Petals">
>     <ExtensionNode name="Petal" type="Mono.Addins.TypeExtensionNode"/>
>   </ExtensionPoint>
>
> from extension addin file:
>
>   <Extension path = "/Stems/Petals">
>     <Petal id="RichContent"
> type="Swivel.Stems.Controllers.RichContentController" />
>   </Extension>
>
> from the host dll:
>
> namespace Swivel.Stems.Controllers
> {
>
> /// <summary>
> /// Interface for petals.
> /// </summary>
> public interface IPetal
> {
>             ...
>         }
> }
>
> from the addin dll:
>
> namespace Swivel.Stems.Controllers
> {
>     public class RichContentController : Controller, IPetal
>     {
>     }
> }
>
> and from the code that loads the extensions in the host dll:
>
> foreach (TypeExtensionNode node in AddinManager.GetExtensionNodes("/
> Stems/Petals"))
> {
> IPetal petal = (IPetal)node.CreateInstance();
> }
>
> It throws an exception on the CreateInstance call:
>
> Unable to cast object of type
> 'Swivel.Stems.Controllers.RichContentController' to type
> 'Swivel.Stems.Controllers.IPetal'.
>
> It seems like this cast is perfectly reasonable. I don't understand
> what's going wrong. In the examples on the site, the extensions only
> implement the interface, and don't subclass anything else. Is this not
> something that's supported?
>
> Thanks.
>
> >

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[Andy Selvig]

Great, thanks! I was accidentally copying the host assembly into the addin directory along with the addin assembly. Works well now. This exception is understandable but it could be a little more specific.

On Tue, Oct 13, 2009 at 2:50 AM, Lluis Sanchez <slluis@...> wrote:

The most probable cause of the error is that you have several copies of
the host assembly in different locations. .NET considers that types
coming from different assembly locations are different.

El dg 11 de 10 de 2009 a les 11:19 -0700, en/na Andy Selvig va escriure:

> Hi-
>
> I have an application using Mono.Addins but I'm having trouble
> creating instances of the extension points. The addin itself is being
> detected and loading fine, but when I try to create an instance from
> an extension node, I get an exception stating that I can't perform the
> conversion. I've pasted the relevant code below.
>
> >From host addin file:
>
>   <ExtensionPoint path = "/Stems/Petals">
>     <ExtensionNode name="Petal" type="Mono.Addins.TypeExtensionNode"/>
>   </ExtensionPoint>
>
> from extension addin file:
>
>   <Extension path = "/Stems/Petals">
>     <Petal id="RichContent"
> type="Swivel.Stems.Controllers.RichContentController" />
>   </Extension>
>
> from the host dll:
>
> namespace Swivel.Stems.Controllers
> {
>
>       /// <summary>
>       /// Interface for petals.
>       /// </summary>
>       public interface IPetal
>       {
>             ...
>         }
> }
>
> from the addin dll:
>
> namespace Swivel.Stems.Controllers
> {
>     public class RichContentController : Controller, IPetal
>     {
>     }
> }
>
> and from the code that loads the extensions in the host dll:
>
> foreach (TypeExtensionNode node in AddinManager.GetExtensionNodes("/
> Stems/Petals"))
> {
>       IPetal petal = (IPetal)node.CreateInstance();
> }
>
> It throws an exception on the CreateInstance call:
>
> Unable to cast object of type
> 'Swivel.Stems.Controllers.RichContentController' to type
> 'Swivel.Stems.Controllers.IPetal'.
>
> It seems like this cast is perfectly reasonable. I don't understand
> what's going wrong. In the examples on the site, the extensions only
> implement the interface, and don't subclass anything else. Is this not
> something that's supported?
>
> Thanks.
>
> >

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