Help required with interop

[Jon Skeet]

I'm trying to speed up a data migration tool I'm writing that uses COM
interop. Currently I'm accessing each field within a record
individually, which works, but means going across the managed/unmanaged
boundary a heck of a lot.

The COM object I'm working with has a method which I'm sure *should*
help, but I can't get it to work. It's described in the documentation
as:

GetDataEx method:

Description: Returns an array of strings containing the data for each
field specified in an array of fields.

Syntax: GetDataEx iFieldArray, szValueArray

Parameters: iFieldArray Returns an array of short integers (or
pointers to short integers in Visual C++)
that represent the field IDs of fields
for which to get the data contained in the
fields.

szValueArray Returns an array of strings (or BSTRs in
Visual C++) for the data that is returned for
the specified fields. The same number of
elements must be specified for the
iFieldArray and the szValueArray parameters.

Note: In Visual C++, use VARIANT.pparray instead of Variant.parray for
pointers to elements in the array.

Return type: void

Example: [irrelevant stuff snipped]

Dim IdArray(10) as Integer
Dim OutputArray(10) as String

' Snip getting the appropriate db object

IdArray(0) = 5
IdArray(1) = 6
IdArray(2) = 10
IdArray(3) = 15

db.GetDataEx IdArray OutputArray



Now, I've tried a number of ways of doing this, but none of them have
worked. The most obvious one is something like:

short[] fields = new short[]{1};
string[] values = new string[1];

db.GetDataEx (fields, values);

but that sets an error code of "invalid parameter" - as does everything
else I try.

Any light anyone could shed on this would be much appreciated...

 

[Lee Alexander]

Does that help at all?
Not really. If you have the tlb file then you can load it up using the
Ole/Com object viewer found under the tools menu of dev studio. This might
give you a bit more info on the method.

Regards
Lee

From the documentation it looks like it expects and array of pointers to
integers. Whereas you are passing a pointer to an array of integers.

Yup - I wondered about that. I tried declaring it as object[] so that
boxing would take place, hoping that the reference would effectively be
a pointer to a short. It didn't help...

Could
this be the problem? Do you have the IDL for the offending function??

I don't, but I have the relevant sections of the tli/tlh files (with
names changed to protect the innocent. From the tli file:

inline HRESULT [Removed]::I[Removed]::GetDataEx
(const _variant_t & vFieldArray, const _variant_t & vValueArray )
{
return _com_dispatch_method(this, 0xe0, DISPATCH_METHOD, VT_EMPTY,
NULL, L"\x000c\x000c", &vFieldArray,
&vValueArray);
}

Does that help at all?

 

[Jon Skeet]

Not really. If you have the tlb file then you can load it up using the
Ole/Com object viewer found under the tools menu of dev studio. This might
give you a bit more info on the method.

Aha. Cheers - sorry, it's a while since I've done any "real" COM work,
and I didn't do much then

Hmm. It doesn't seem to give much more info:

[id(0x000000e0)]
void GetDataEx(
VARIANT vFieldArray,
VARIANT vValueArray);

Distinctly unhelpful

Never mind - I've found another way of speeding things up considerably:
loading the whole database into memory to start with! I think a lot of
the time was being spent jumping around different records in the
database...

 

[Lee Alexander]

Never mind - I've found another way of speeding things up considerably:
okies.

Regards
Lee

Not really. If you have the tlb file then you can load it up using the
Ole/Com object viewer found under the tools menu of dev studio. This might
give you a bit more info on the method.

Aha. Cheers - sorry, it's a while since I've done any "real" COM work,
and I didn't do much then

Hmm. It doesn't seem to give much more info:

[id(0x000000e0)]
void GetDataEx(
VARIANT vFieldArray,
VARIANT vValueArray);

Distinctly unhelpful

Never mind - I've found another way of speeding things up considerably:
loading the whole database into memory to start with! I think a lot of
the time was being spent jumping around different records in the
database...