Beginner's problem

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3 total messages Started by Jim Melsom Wed, 10 Nov 1999 00:00

#1392

Author: Jim Melsom
Date: Wed, 10 Nov 1999 00:00

21 lines
1259 bytes

I'm using MIDAS for the first time and have hit a snag.

I'm following the simple MIDAS example in CPPB4 Unleashed (using CPPB4
Enterprise with Patch 1 installed). My MIDAS server has an exported
TProvider which is connected to a valid TTable, and it has been
registered.

The client uses a TDCOMConnection, and it starts the server properly
(the server is running on my local machine). It has a TClientDataset
that references the server's provider.

This is the problem: as soon as the TClientDataset's Active property is
set to true, the following error occurs:

"src->QueryInterface(GetIID(),(LPVOID*)(&intf)). No such interface
exists ..."

I know what it means, but not what's causing it. Does anyone?


Thanks...

Re: Beginner's problem

#1393

Author: Jim Melsom
Date: Wed, 10 Nov 1999 00:00

11 lines
1095 bytes

Jim Melsom wrote:
> This is the problem: as soon as the TClientDataset's Active property is
> set to true, the following error occurs:
> "src->QueryInterface(GetIID(),(LPVOID*)(&intf)). No such interface
> exists ..."

I see this same thing was asked and answered earlier and is caused by
the code generated (or not generated) when exporting a TProvider.
Casting the return value of  get_<aprovider> to IProvider* works around
it. Kind of a tricky gotcha for newbies but once again it shows how
helpful these newsgroups are.

Re: Beginner's problem

#1402

Author: John Graham
Date: Sun, 14 Nov 1999 00:00

30 lines
1603 bytes

What that means is after the remote data module source code has been
generated, edit all the functions in the ...Impl.cpp source file that
contain:

    *Value = IProv;

so that they read:

    *Value = (IProvider*)IProv;

Some day Borland may see fit to fix this problem.  I was hoping it would be
fixed in update 2; no such luck.  Perhaps they're not aware of the problem?
Or perhaps they don't know how to fix it?

Regards,
John

Jim Melsom wrote:

> Jim Melsom wrote:
> > This is the problem: as soon as the TClientDataset's Active property is
> > set to true, the following error occurs:
> > "src->QueryInterface(GetIID(),(LPVOID*)(&intf)). No such interface
> > exists ..."
>
> I see this same thing was asked and answered earlier and is caused by
> the code generated (or not generated) when exporting a TProvider.
> Casting the return value of  get_<aprovider> to IProvider* works around
> it. Kind of a tricky gotcha for newbies but once again it shows how
> helpful these newsgroups are.

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