GetClassName from an Interface

  • Thread starter Thread starter Simon Woods
  • Start date Start date
S

Simon Woods

Hi

Still trying to get to grips with VB.Net so sorry if these seem silly
questions ...

I have an object which is implementing a secondary interface. I want to
get the name of the underlying object.

My Interface is:

Public Interface ICommand
Sub Execute
End Interface

ATM, I'm doing

name = DirectCast(myInterfacedObject, Object).GetType.Name

Are there better ways of doing this? Examples I've seen in C# seem to
suggest that you can call the GetType off the Interface itself.

Obviously I could put the Name property onto the interface, but I'm
wondering if there are some other ways I could do this?

Also, what is going on when DirectCast is called? Is the object being
copied to somewhere else in memory or is a different address in memory
being used to retrieve the Type info?

Thanks

Simon
 
Simon Woods said:
Hi

Still trying to get to grips with VB.Net so sorry if these seem
silly questions ...

I have an object which is implementing a secondary interface. I want
to get the name of the underlying object.
Click to expand...
My Interface is:

Public Interface ICommand
Sub Execute
End Interface

ATM, I'm doing

name = DirectCast(myInterfacedObject, Object).GetType.Name

Are there better ways of doing this? Examples I've seen in C# seem
to suggest that you can call the GetType off the Interface itself.

Obviously I could put the Name property onto the interface, but I'm
wondering if there are some other ways I could do this?
Click to expand...

Why? Purpose for getting type information?

Also, what is going on when DirectCast is called?
Click to expand...

The type of the reference is changed to the destination type.
Is the object
being copied to somewhere else in memory
No

or is a different address
in memory being used to retrieve the Type info?
Click to expand...

The Object's Gettype method is used to get the type info. The interface does
not have a GetType method.


Armin
 
Armin said:
Why? Purpose for getting type information?
Click to expand...

I'm learning some design patterns and am translating some java code ...
It has been translated into c# okay, but vb doen't give you the GetType
off the interface.
 
Simon Woods said:
I'm learning some design patterns and am translating some java code
... It has been translated into c# okay, but vb doen't give you the
GetType off the interface.
Click to expand...


Shared Function GetTheType(ByVal o As Object) As System.Type
Return o.GetType
End Function


Armin
 
Simon said:
I have an object which is implementing a secondary interface. I want to
get the name of the underlying object.
Click to expand...

"Name" or "Type"?
name = DirectCast(myInterfacedObject, Object).GetType.Name

Are there better ways of doing this? Examples I've seen in C# seem to
suggest that you can call the GetType off the Interface itself.
Click to expand...

You /should/ be able to.
The only thing to watch out for is some "bright-spark" may have
Shadow'ed the GetType method and made it do something completely
different - stupid, I know, but it's the kind of thing Developers /love/
to do - "up-casting" to Object gets around this by using Object's most
basic implementation.
Obviously I could put the Name property onto the interface, but I'm
wondering if there are some other ways I could do this?
Click to expand...

If you're after a Name property on a class that you know about, just
cast the reference to the required Type (after checking that you /can/,
of course):

If TypeOf myInterfacedObject Is NamedThing Then
sName = DirectCast( myInterfacedObject, NamedThing ).Name
End If
Also, what is going on when DirectCast is called? Is the object being
copied to somewhere else in memory or is a different address in memory
being used to retrieve the Type info?
Click to expand...

Nope. If you've ever worked with 'C++' or 'C#', you'll have come across
the likes of:

int * pointerToInteger = 0 ;
char * pointerToChar = (char *)pointerToInteger ;

The second line takes a pointer to an integer value and blithely stuffs
it into a variable that's supposed to point to a character value. Both
pointers refer to the same chunk of memory, but treat it as different
"types".

DirectCast does much the same thing. It tells the compiler to treat the
given "object reference" (a.k.a. strongly-typed Pointer) as a reference
to a /different/ Type. However, it does go a little bit further and
checks the object's inheritance hierarchy and, if it can't make the cast
you've asked it to, it'll throw an Exception on you:

Class Class1
Public Property Name
Class Class2 Inherits Class1
Class Class3 Inherits Class2
Class Class4

Dim c2 as New Class2
?DirectCast( c2, Class1 ).Name ' OK
?DirectCast( c2, Class4 ).Name ' Boom!
?DirectCast( c2, Class3 ).Name ' Boom! Think about this one

HTH,
Phill W.
 
Phill said:
"Name" or "Type"?


You /should/ be able to.
The only thing to watch out for is some "bright-spark" may have
Shadow'ed the GetType method and made it do something completely
different - stupid, I know, but it's the kind of thing Developers /love/
to do - "up-casting" to Object gets around this by using Object's most
basic implementation.


If you're after a Name property on a class that you know about, just
cast the reference to the required Type (after checking that you /can/,
of course):

If TypeOf myInterfacedObject Is NamedThing Then
sName = DirectCast( myInterfacedObject, NamedThing ).Name
End If


Nope. If you've ever worked with 'C++' or 'C#', you'll have come across
the likes of:

int * pointerToInteger = 0 ;
char * pointerToChar = (char *)pointerToInteger ;

The second line takes a pointer to an integer value and blithely stuffs
it into a variable that's supposed to point to a character value. Both
pointers refer to the same chunk of memory, but treat it as different
"types".

DirectCast does much the same thing. It tells the compiler to treat the
given "object reference" (a.k.a. strongly-typed Pointer) as a reference
to a /different/ Type. However, it does go a little bit further and
checks the object's inheritance hierarchy and, if it can't make the cast
you've asked it to, it'll throw an Exception on you:

Class Class1
Public Property Name
Class Class2 Inherits Class1
Class Class3 Inherits Class2
Class Class4

Dim c2 as New Class2
?DirectCast( c2, Class1 ).Name ' OK
?DirectCast( c2, Class4 ).Name ' Boom!
?DirectCast( c2, Class3 ).Name ' Boom! Think about this one

HTH,
Phill W.
Click to expand...

That's very helpful ... thanks very much (to Armin as well)

Simon
 
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