Re: .NET and COM Interop
From: Nick Hall (nickh_at_aslan.nospam.co.uk)
Date: 07/23/04
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Date: Fri, 23 Jul 2004 13:23:35 +0100
Comments inline: -
"Stephan Scheidl" <stephan.scheidl@gmx.at> wrote in message
news:40ffd6d2$1@e-post.inode.at...
> I have written a class library in c# and want to use it in VB6. Everything
> works fine so far but when I try to assign a value (an array of type
defined
> in c#) to a property definded on the c# side the vb compiler does not want
> to compile. Reading access to the property is working.
> I added a function that sets the array and it worked, so what is going
wrong
> in the property call?
> I extracted the IDL code from the type library and there is the problem:
>
>
> [
> uuid(D9284674-EBA7-4C9B-A823-65193E0D5FC3),
> version(1.0),
> custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, xxxxxx.IColorRangeSelectEx)
> ]
> dispinterface IColorRangeSelectEx {
> properties:
> methods:
> [id(0x60020000)]
> void SetColorSteps([in, out] SAFEARRAY(ColorStep)* Steps);
> [id(0x60020001)]
> SAFEARRAY(ColorStep) GetColorSteps();
> [id(0x60020002), propget]
> SAFEARRAY(ColorStep) ColorSteps();
> [id(0x60020002), propput]
> void ColorSteps([in] SAFEARRAY(ColorStep) rhs);
> };
>
> Take a look at the SetColorSteps and propput definitions. How can I solve
> this???
>
I had the same problem a while back. It seems to be a limitation of the
current marshalling engine. I posted a question on here a while back but
no-one seemed to have any explanation. The only way I could get this to
work as I wanted to was to do the following: -
1. Define the interface in a type library (with the extra level of
indirection that VB needs on the propput);
2. Reference the created type library from my project;
3. To implement the interface properly you have to be a bit sneaky. If you
try to implement the property properly, the compiler will complain. If,
however, you define the get/set methods explicitly, the compiler is
satisfied.
For example, I defined the following interface in a type library -
interface ISignature : IDispatch {
.....
[id(0x60020002), propget]
HRESULT SignatureBytes([out, retval] SAFEARRAY(unsigned char)* retVal);
[id(0x60020002), propput]
HRESULT SignatureBytes([in] SAFEARRAY(unsigned char)* retVal);
....
}
This comes though in DotNet as : -
public System.Array SignatureBytes[get, set]
Which I implemented like this in my class: -
Array ISignature.get_SignatureBytes()
{
return this.SignatureBytes;
}
void ISignature.set_SignatureBytes(ref Array value)
{
this.SignatureBytes = (Byte[]) value;
}
This works in the current version but a future version could stop this
working. Hopefully, they'll make the proper fix (which is to allow arrays
to be exposed to COM in a VB-friendly manner).
>
>
> Another question:
>
> Everytime I change some code an recompile the dll I have to fix the
> reference in VB. I have assigned guids to all public types and I checked
> that the entries in the registry do not change. What am I doing wrong?
>
>
>
> Many thanks in advance
>
>
>
> Stephan Scheidl
>
>
Have you assigned a GUID to the assembly (i.e. the type library)? I had
this problem initially because there is a difference in behaviour between VB
and C# - VB automatically creates an [assembly: Guid(...)] attribute in the
AssemblyInfo file whereas C# does not. Otherwise, I think the type library
GUID is generated automatically each time the assembly is compiled, causing
COM clients to lose track.
Hope this helps,
Nick Hall
- Next message: Gerhard Menzl: "Very strange RCW behaviour with VARIANTs/SAFEARRAYs in Managed C++"
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