Type casting object type to user defined class or interface

[Programmer]

I am making a project in which i have one interface ITest,
and a class which is implementing that interface.

I am making object of that class using

object obj=Activator.C reateInstance(" TypeName");
ITest objITest =(ITest) obj;

It is giving error explicit typecasting not allowed

can any body help on this

[Jon Skeet [C# MVP]]

Re: Type casting object type to user defined class or interface

Programmer <gurjinder@bees ys.com> wrote:[color=blue]
> I am making a project in which i have one interface ITest,
> and a class which is implementing that interface.
>
> I am making object of that class using
>
> object obj=Activator.C reateInstance(" TypeName");
> ITest objITest =(ITest) obj;
>
> It is giving error explicit typecasting not allowed[/color]

What is the *exact* error message, and when are you getting it? Do you
have more than one assembly involved? If so, you might be running into
the problem described at http://www.pobox.com/~skeet/csharp/plugin.html

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Rashad Rivera]

Re: Type casting object type to user defined class or interface

In this case you need to look at the work "explicit" and see that it is
telling you not to cast it with the "(ITest)" because there is no need. Try
this and it should work

object obj=Activator.C reateInstance(" TypeName");
ITest objITest = obj; // Don't use a cast for like types

- Rashad Rivera
Department of State/NCC

"Programmer " <gurjinder@bees ys.com> wrote in message
news:06d301c3db 2c$cbcd01c0$a40 1280a@phx.gbl.. .[color=blue]
> I am making a project in which i have one interface ITest,
> and a class which is implementing that interface.
>
> I am making object of that class using
>
> object obj=Activator.C reateInstance(" TypeName");
> ITest objITest =(ITest) obj;
>
> It is giving error explicit typecasting not allowed
>
> can any body help on this
>[/color]

[gurjinder kharbanda]

Re: Type casting object type to user defined class or interface


thanxs



*** Sent via Developersdex http://www.developersdex.com ***
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[Jon Skeet [C# MVP]]

Re: Type casting object type to user defined class or interface

Rashad Rivera <rashadrivera@N O_____SPAM__.ho tmail.com> wrote:[color=blue]
> In this case you need to look at the work "explicit" and see that it is
> telling you not to cast it with the "(ITest)" because there is no need. Try
> this and it should work
>
> object obj=Activator.C reateInstance(" TypeName");
> ITest objITest = obj; // Don't use a cast for like types[/color]

No it shouldn't. There's no way an implicit cast is going to exist from
object to a particular interface, is there?

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Rashad Rivera]

Re: Type casting object type to user defined class or interface

There is no need. In the case you described above, you got an
instance to the very interface you are attempting to cast too. But to
answer your question, yes! But it depends on what language and what
you are doing. In C++ you use the IUnknown::Querr yInterface(), in C#
you just directly cast with the interface alone:

namespace MyTest {
public interface ITest {
bool Print();
}

public class Test : ITest {
public bool Print() {
// do something
}
}
}
Test t = new Test();
ITest i = t;
i.Print(); // result is printed

....

but in JScript 5.5 and less, you never have access to an interface
directly:


// assuming you registered with string named
var t = new ActiveXObject(' MyTest.Test'); // OK
var t2 = new ActiveXObject(' MyTest.ITest'); // ERROR, ITEST is not in
REGISTRY

Does this answer your question?
- Rashad Rivera
Department of State/NCC

Jon Skeet [C# MVP] <skeet@pobox.co m> wrote in message news:<MPG.1a706 1a3e7069f10989e 31@msnews.micro soft.com>...[color=blue]
> Rashad Rivera <rashadrivera@N O_____SPAM__.ho tmail.com> wrote:[color=green]
> > In this case you need to look at the work "explicit" and see that it is
> > telling you not to cast it with the "(ITest)" because there is no need. Try
> > this and it should work
> >
> > object obj=Activator.C reateInstance(" TypeName");
> > ITest objITest = obj; // Don't use a cast for like types[/color]
>
> No it shouldn't. There's no way an implicit cast is going to exist from
> object to a particular interface, is there?[/color]

[Jon Skeet [C# MVP]]

Re: Type casting object type to user defined class or interface

Rashad Rivera <rashadrivera@h otmail.com> wrote:[color=blue]
> There is no need. In the case you described above, you got an
> instance to the very interface you are attempting to cast too. But to
> answer your question, yes! But it depends on what language and what
> you are doing. In C++ you use the IUnknown::Querr yInterface(), in C#
> you just directly cast with the interface alone:[/color]

Yes, but you *do* need to directly cast.

My point was that the sample code you gave (in C#) was never going to
work, and your explanation was definitely wrong.

If you can give *any* code (which doesn't alias "object" to some other
type) where you can use your code:

object obj=Activator.C reateInstance(" TypeName");
ITest objITest = obj; // Don't use a cast for like types

I'll be very surprised.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too