VB Late Binding Vs ASP - Using Interop Services

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Christopher Pragash - 27 Aug 2003 04:04 GMT

Hello All,

I have a problem with ASP & VB 6 using an Interop Assembly . I marshal an
array in VB.NET, mark it as <MarshalAsAttribute(UnmanagedType.LPArray)>, and
I am able to retrieve the correct values in VB6 using Late Binding, not
predefining specific datatypes for the array. But ASP seems to have a
problem...and it crashes.

Following is the code sample in both VB and ASP

'All objects are declared as Variants...
'Lookup.LookupItems returns an Array marshled by VB.NET and marked as
<MarshalAsAttribute(UnmanagedType.LPArray)>

For Each objlookupItem In lookup.LookupItems
txtoutput.Text = txtoutput.Text & objlookupItem.Description & Chr(13) &
Chr(10)
Next

In vb the above code returns the right values. In ASP returns:
Error Type:
Microsoft VBScript runtime (0x800A000D)
Type mismatch: 'LookupItems'

Any ideas on why the problem in ASP and how I could resolve this?

Thanks in advance,

Chris

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Mattias Sj?gren - 27 Aug 2003 12:37 GMT

Christopher,

Why do you use <MarshalAsAttribute(UnmanagedType.LPArray)>? SAFEARRAYs
are more OLE automation friendly.

Mattias

Signature

Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/
Please reply only to the newsgroup.

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Christopher Pragash - 27 Aug 2003 13:32 GMT

Mattias,

If I use the SafeArray attribute, VB does not understand the array, I get
errors irrespective of whether I use early binding or late binding. Any
ideas how I could marshal an array of objects from VB.NET To ASP??
Appreciate your response.

Thanks,
Chris

> Christopher,
>
> Why do you use <MarshalAsAttribute(UnmanagedType.LPArray)>? SAFEARRAYs
> are more OLE automation friendly.
>
> Mattias

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Tim Golisch - 29 Aug 2003 20:57 GMT

One thing to keep in mind is that ASP can't handle typed arrays. You
can only pass an array of variants. Any other typed array will cause a
type mismatch error (even though ASP should have no problem converting
the elements of the array).

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Laurent De Greef - 01 Sep 2003 16:36 GMT

You say that ASP can handle SAFEARRAY's of variants but the following C#
method :

public int SetStringArray([MarshalAs(UnmanagedType.SafeArray,
SafeArraySubType=(VarEnum.VT_VARIANT))] object[] stringArray)
{
return stringArray.Length;
}

fails when called from this VBScript code :

Dim dotNetArray
set dotNetArray = CreateObject("COMMarshalling.DotNetArray")
Dim strArray(3)
strArray(0) = "FirstString"
strArray(1) = "SecondString"
strArray(2) = "ThirdString"
Dim arCount
arCount = dotNetArray.SetStringArray(strArray)

I get the following error message :
Invalid procedure call or argument: 'SetStringArray'

According to me, the problem is that VBScript can only handle
SAFEARRAY's encapsuled into a VARIANT parameter as it works in C++ :
STDMETHOD (SetStringArray)(/*[in]*/VARIANT vArray)

I don't see how .NET can support this kind of parameter...

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