Casting

[shapper]

Hello,

I have created a class that inherits MembershipUser:
public class UserHelper : MembershipUser {
....

Then I am creating a user as follows:
UserHelper user = (UserHelper)Mem bership.CreateU ser("me", "pass",
"me@domain.com" , null, null, true, null, out status);

Membership.Crea teUser returns a MembershipUser

But I get an error:
Unable to cast object of type 'System.Web.Sec urity.Membershi pUser' to
type 'MyApp.Security .Membership.Use rHelper'.

If I don't cast it, which means, using:
UserHelper user = Membership.Crea teUser("me", "pass", "me@domain.com" ,
null, null, true, null, out status);

It does not compile and I get the error:
Cannot implicitly convert type 'System.Web.Sec urity.Membershi pUser' to
'MyApp.Security .Membership.Use rHelper'. An explicit conversion exists
(are you missing a cast?)

What am I doing wrong?

Thanks,
Miguel

[Peter Duniho]

Re: Casting

On Sat, 01 Nov 2008 10:28:10 -0700, shapper <mdmoura@gmail. comwrote:

Hello,
>
I have created a class that inherits MembershipUser:
public class UserHelper : MembershipUser {
...
>
Then I am creating a user as follows:
UserHelper user = (UserHelper)Mem bership.CreateU ser("me", "pass",
"me@domain.com" , null, null, true, null, out status);
>
Membership.Crea teUser returns a MembershipUser

If the object is not a UserHelper instance, you simply cannot cast it to
UserHelper. It's just not possible.

Note that in the second case, where you don't cast it and the compiler
says "an explicit conversion exists", it only means that in the
syntactical sense. It has no way to verify whether the conversion will
actually _succeed_...jus t that you can attempt it explicitly with a cast.

Pete

[Tim Roberts]

Re: Casting

shapper <mdmoura@gmail. comwrote:

>
>I have created a class that inherits MembershipUser:
>public class UserHelper : MembershipUser {
>...
>
>Then I am creating a user as follows:
>UserHelper user = (UserHelper)Mem bership.CreateU ser("me", "pass",
>"me@domain.com ", null, null, true, null, out status);
>
>Membership.Cre ateUser returns a MembershipUser
>
>But I get an error:
>Unable to cast object of type 'System.Web.Sec urity.Membershi pUser' to
>type 'MyApp.Security .Membership.Use rHelper'.
>
>If I don't cast it, which means, using:
>UserHelper user = Membership.Crea teUser("me", "pass", "me@domain.com" ,
>null, null, true, null, out status);
>
>It does not compile and I get the error:
>Cannot implicitly convert type 'System.Web.Sec urity.Membershi pUser' to
>'MyApp.Securit y.Membership.Us erHelper'. An explicit conversion exists
>(are you missing a cast?)
>
>What am I doing wrong?

You're casting in the wrong direction. If you have a UserHelper, you can
cast it to a MembershipUser, but you cannot safely start with a base object
and cast it to a derived class. What would happen to any additional
members you might have added? They wouldn't be present in the
MembershipUser instance.

In this case, you will have to use composition instead of inheritance. Add
a MembershipUser instance to UserHelper ad a member, call CreateUser, and
pass the MembershipUser object you get to the constructor for UserHelper.
--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.