I am working on a project that I would like to have some extensibility for
later. So with this I am using interfaces to pass objects to derived classes.
However I am running into a situation where two seperate classes won't cast
each other even though they implement the same interface. The classes are
identical yet won't convert. Here is (briefly) what I am talking about:

public interface IReturnObject
{
Guid ID { get; set; }
string Status { get; set; }
string Message { get; set; }
}

public class Result : IReturnObject
{
//implements code here
}

public class Response : IReturnObject
{
//implements code here
}


NOTE: The above two classes are in different namespaces such that Result is
in System.Application1.Result and Response is in System.Application.Response.

So when I use this in a client app and try to cast these two classes against
each other it compiles but at runtime I get "Specified cast is not valid"
with a System.ArguementException.

Any help would be greatly appreciated.

<"=?Utf-8?B?Q2xpbnQgSGlsbA==?=" <Clint
(E-Mail Removed)>> wrote:
> I am working on a project that I would like to have some extensibility for
> later. So with this I am using interfaces to pass objects to derived classes.
> However I am running into a situation where two seperate classes won't cast
> each other even though they implement the same interface. The classes are
> identical yet won't convert. Here is (briefly) what I am talking about:
>
> public interface IReturnObject
> {
> Guid ID { get; set; }
> string Status { get; set; }
> string Message { get; set; }
> }
>
> public class Result : IReturnObject
> {
> //implements code here
> }
>
> public class Response : IReturnObject
> {
> //implements code here
> }
>
>
> NOTE: The above two classes are in different namespaces such that Result is
> in System.Application1.Result and Response is in System.Application.Response.
>
> So when I use this in a client app and try to cast these two classes against
> each other it compiles but at runtime I get "Specified cast is not valid"
> with a System.ArguementException.

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

Note that you *won't* be able to cast an instance of Result to Response
or vice versa - but you should be able to cast each of them to
IReturnObject.

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

I think you got the interface idea wrong. Many classes do implement, for
example, the IEnumerable interface; arrays do so, ArrayList, but also
HashTable and many other classes. Still you can't cast a HashTable to an
array or vice versa - they are unrelated classes and the only way to
"convert" them is to copy all the data item by item. The only thing you can
do is cast each of them to the IEnumerable interface. The idea is to write
code that only accesses classes through interfaces, so you can easily change
the implementation, as in:

void Output (IEnumerable lst)
{ foreach (object x in lst) Console.Writeline(x); }

This function will work for arrays, arraylists, hashtables...

Hope this helps,

Niki

"Clint Hill" <Clint (E-Mail Removed)> wrote in
news:E2497A2F-5EC3-44A5-9ECC-(E-Mail Removed)...
> I am working on a project that I would like to have some extensibility for
> later. So with this I am using interfaces to pass objects to derived
classes.
> However I am running into a situation where two seperate classes won't
cast
> each other even though they implement the same interface. The classes are
> identical yet won't convert. Here is (briefly) what I am talking about:
>
> public interface IReturnObject
> {
> Guid ID { get; set; }
> string Status { get; set; }
> string Message { get; set; }
> }
>
> public class Result : IReturnObject
> {
> //implements code here
> }
>
> public class Response : IReturnObject
> {
> //implements code here
> }
>
>
> NOTE: The above two classes are in different namespaces such that Result
is
> in System.Application1.Result and Response is in
System.Application.Response.
>
> So when I use this in a client app and try to cast these two classes
against
> each other it compiles but at runtime I get "Specified cast is not valid"
> with a System.ArguementException.
>
> Any help would be greatly appreciated.

Clint Hill <(E-Mail Removed)> wrote:

<snip>

Right. So you really are trying to cast an object to a class which it
isn't. You can't do that. You should use an interface which supports
everything you need.

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Thank you. I believe I understand it now.

"Niki Estner" wrote:

> I think you got the interface idea wrong. Many classes do implement, for
> example, the IEnumerable interface; arrays do so, ArrayList, but also
> HashTable and many other classes. Still you can't cast a HashTable to an
> array or vice versa - they are unrelated classes and the only way to
> "convert" them is to copy all the data item by item. The only thing you can
> do is cast each of them to the IEnumerable interface. The idea is to write
> code that only accesses classes through interfaces, so you can easily change
> the implementation, as in:
>
> void Output (IEnumerable lst)
> { foreach (object x in lst) Console.Writeline(x); }
>
> This function will work for arrays, arraylists, hashtables...
>
> Hope this helps,
>
> Niki
>
> "Clint Hill" <Clint (E-Mail Removed)> wrote in
> news:E2497A2F-5EC3-44A5-9ECC-(E-Mail Removed)...
> > I am working on a project that I would like to have some extensibility for
> > later. So with this I am using interfaces to pass objects to derived
> classes.
> > However I am running into a situation where two seperate classes won't
> cast
> > each other even though they implement the same interface. The classes are
> > identical yet won't convert. Here is (briefly) what I am talking about:
> >
> > public interface IReturnObject
> > {
> > Guid ID { get; set; }
> > string Status { get; set; }
> > string Message { get; set; }
> > }
> >
> > public class Result : IReturnObject
> > {
> > //implements code here
> > }
> >
> > public class Response : IReturnObject
> > {
> > //implements code here
> > }
> >
> >
> > NOTE: The above two classes are in different namespaces such that Result
> is
> > in System.Application1.Result and Response is in
> System.Application.Response.
> >
> > So when I use this in a client app and try to cast these two classes
> against
> > each other it compiles but at runtime I get "Specified cast is not valid"
> > with a System.ArguementException.
> >
> > Any help would be greatly appreciated.
>
>
>