Re: Which COM interface to export an object into a particular format - COM Discussion Boards

Re: Which COM interface to export an object into a particular format

21-Oct-05 22:10

I would like my COM object to expose the functionality to export itself into different binary representations into an output stream. E.g. to render itself into a stream as PDF or as JPEG, etc. The functionality itself is already available, but I don't know how to expose this function in terms of standard COM interfaces.
I looked at the IPersistXXX interfaces but they don't allow to specify the target format but assume that the format is inherent to the object. Also for every output format there are potentially format dependent options that need to be passed in.
IPersistMoniker looked promising but I am not sure if the intent of this interface is the export into different formats.
I would like to reuse existing COM interfaces if possible rather than defining my own interface.

What do you recommend?

Best regards
Carsten

Vi223-Oct-05 18:33

Vi2

23-Oct-05 18:33

There is the IPersistFile which has Load(filename) and Save(filename).

With best wishes,
Vita

Re: Which COM interface to export an object into a particular format

Carsten Leue23-Oct-05 22:08

Re: Which COM interface to export an object into a particular format

23-Oct-05 22:08

Hi Vita.

Right, but how does the interface allow me to export my object? I would guess the correct format by evaluating the file extension, but that won't work if want to stream the content instead of writing it to a file (IPersistStream). Also IPersistFile does not allow me to pass extra information to configure the export process, such as target width/height of an exported bitmap or the compression ratio for JPEG.

Vi224-Oct-05 0:10

Vi2

24-Oct-05 0:10

Right, but how does the interface allow me to export my object?

As usual IPersist* interface. If you try to find some export interface, so you can use the exact IPersistFile. If you aren't able to choice the export interface, you should implement the exact one required by client.

I would guess the correct format by evaluating the file extension, but that won't work if want to stream the content instead of writing it to a file (IPersistStream).

The stream stores the binary data which presents this object (see OleLoadFromStream). There is no matter which format the object used to be stored.

With best wishes,
Vita

Re: Which COM interface to export an object into a particular format

Carsten Leue24-Oct-05 5:14

24-Oct-05 5:14

Hi Vita.

I guess I want to make a different point. The COM object that I have represents a graphic with an internal binary representation that is specifc to my application. I want to export this graphic to JPEG into a stream (or a number of other formats). The JPEG representation is not enough to recreate my graphics, so it is not equivalent to persisting my object, I just want to export it to a stream (not to a file), e.g. to pipe it into another filter stream or to return it as a response to an http request.

Somewhat like this (pseudocode):

<br />
IUnknown* pMyObject = ...<br />
IStream* pOut = ...  // E.g. via SHCreateStreamOnFile(...)<br />
<br />
IExport* pExport;<br />
pMyObject->QueryInterface(IID_IExport, (LPVOID*) &pExport);<br />
<br />
LPCWSTR mimeType = L"image/jpeg";<br />
IBindCtx* pJpegOptions = ...<br />
IPersistStream* pPersStream;<br />
pExport->get_Persister(&pPersStream, mimeType, pJpegOptions);<br />
<br />
pPersStream->Save(pOut, FALSE);<br />
<br />
// export the same instance into a different format<br />
<br />
mimeType = L"application/postscript";<br />
IBindCtx* pPostscriptOptions = ...<br />
pExport->get_Persister(&pPersStream, mimeType, pPostscriptOptions );<br />
<br />
pPersStream->Save(pOut, FALSE);<br />

I wonder if this is the right programming pattern to export an object and if yes, is there a standard interface that corresponds to the IExport in my pseudocode?

I considered using IPersistMoniker like this:

<br />
IUnknown* pMyObject = ...<br />
<br />
IPersistMoniker* pPersMon;<br />
pMyObject->QueryInterface(IID_IPersistMoniker, (LPVOID*) &pPersMon);<br />
<br />
IMoniker* pOutMon;<br />
CreateFileMoniker(L"test.jpg", &pOutMon);<br />
IBindCtx* pJpegOptions = ...<br />
pPersMon->Save(pOutMon, pJpegOptions, FALSE)<br />

Is this the right pattern?

[Message Deleted]

Carsten Leue24-Oct-05 5:14

suggest a good book for COM

24-Oct-05 5:14

[Message Deleted]

einishant21-Oct-05 3:01

einishant

21-Oct-05 3:01

Can any one suggest a good book on COM I do not want that it should cover C++ or object oriented concepts but directly into the com concepts with examples.

Please any one could suggest me a good book which they have probably read.

Nishant J jaiswal

Re: suggest a good book for COM

Carsten Leue21-Oct-05 22:40

Re: suggest a good book for COM

21-Oct-05 22:40

Don Box' books are definitely the best in my opinion.

Essential COM
http://www.amazon.com/gp/product/0201634465/104-1873800-1887156?v=glance&n=283155&n=507846&s=books&v=glance

Effective COM
http://www.amazon.com/gp/product/0201379686/104-1873800-1887156?v=glance&n=283155&n=507846&s=books&v=glance

Carsten

einishant22-Oct-05 2:05

einishant

22-Oct-05 2:05

Thank you Carsten for your help do you also know some ebook or material on the net which is on the same line

NJJ

Re: suggest a good book for COM

Gizzo25-Oct-05 6:59

Gizzo

25-Oct-05 6:59

I recommend you to have a look in the MSDN Library[^]
. There is a lot of information there.

And there are a lot of articles very helpful here in The Code Project. For example...

From Joao C. Morais -- All of them. The articles are a very good introduction to COM Architecture[^]
From Lim Bio Liong -- All of them are indispensables. Have a look in the Beginners section [^].

numnericupdown problem

Mridang Agarwalla20-Oct-05 9:57

Mridang Agarwalla

20-Oct-05 9:57

i want to use the numericupdown control in my application but it doesnt adopt the XP style look. it still has that old classic look even though the rest of the controls have the XP look. How do i so this. I'm sure it's possible becuase the numericupdown control is used in the date tim applet in the control panel having XP looks.

windows update

Mridang Agarwalla20-Oct-05 9:54

Mridang Agarwalla

20-Oct-05 9:54

has anyone seen a project which allows a user to check for windows updates and then update windows.

Identity impersonation per page - possible?

minette20-Oct-05 0:08

minette

20-Oct-05 0:08

I'm working on a web application, in ASP.NET C#, that uses both the Excel object on the server, as well as Crystal Reporting. In order to ensure that the account the web application is running under has access to the Excel object on the server, I set the <identity impersonate="true"> property in the Web.config file.

The problem is that this causes problems when running Crystal Reports. I was not involved with the reports, but as far as I understand the Crystal error is then 'Access is Denied' as it is when the <identity> tag is not in the Web.config file. For now, I have had to disabled the Excel functionality and removed the <identity> tag. I would like to know if there is anyway I could enable the impersonation for one specific page only, without compromising security too much, as clients aren't always happy with that. Or perhaps someone knows of another way around this?

I know that it is possible to set permissions through DCOM etc, but this will complicate implementation and is not desirable.

Thanks

Minette

Going insane over this

odiesback19-Oct-05 5:44

19-Oct-05 5:44

HI All,

Here is the problem:
I have a simple COM server and it compiles and runs with
no errors:
X Code is OK
X Registry Checked OK
X Creates a DLL and TLB OK

Now on client's side:
#import <files> OK

I then created the smart pointers to my interfaces and no errors.
But it crashes when I try to access a funcion using the -> operator.

Then I tried it using raw COM and I get an HRESULT_CODE (505)
When debugging I can track the line below as

hr = CoCreateInstance(CLSID_CoCar, NULL, CLSCTX_INPROC_SERVER,
IID_ICreateCar, (void**)&pCCar);

I get this message: 0x800401f9 Error in the DLL Dead | X|

I have checked everything I could.. what am I missing.

I need some Sleepy | :zzz:

Roger Stoltz20-Oct-05 0:07

Roger Stoltz

20-Oct-05 0:07

Not much for the rest of us to go on here since the only information you provided is that everything is OK but you still get an error... Wink | ;)

Try this:
1. Unreg your component(s)
2. Perform a 'clean' in each project involved
3. Remove all files that are created during the #import (.tli, .tlh)
4. Rebuild all

Post again if the above doesn't remove the error.
And provide some more info while you're at it...

Hope this helps
--
Roger

It's supposed to be hard, otherwise anybody could do it!

odiesback20-Oct-05 7:04

20-Oct-05 7:04

Here is what I know so far...

The client fails to create my COM object and return an
unsuccessful HRESULT.

Back to my server: I cleaned iup, removed all registries, etc,
even created a new project alltogether.

I started my project with an "Empty Win32 DLL" base.

The only difference that I noticed from a copy running under VC6.0 is
that my _i.c and .h files carry the following header:

-----------------------------------------------------------------------------
#pragma warning( disable: 4049 ) /* more than 64k source lines */

/* this ALWAYS GENERATED file contains the IIDs and CLSIDs */

/* link this file in with the server and any clients */

/* File created by MIDL compiler version 6.00.0347 */
/* at Thu Oct 20 10:00:32 2005
*/
/* Compiler settings for CarServerType.idl:
Os, W1, Zp8, env=Win32 (32b run)
protocol : dce , ms_ext, c_ext
error checks: allocation ref bounds_check enum stub_data
VC __declspec() decoration level:
__declspec(uuid()), __declspec(selectany), __declspec(novtable)
DECLSPEC_UUID(), MIDL_INTERFACE()
*/
//@@MIDL_FILE_HEADING( )

#if !defined(_M_IA64) && !defined(_M_AMD64)
----------------------------------------------------------------
I can post the code if you wish

Thanks for your help

Roger Stoltz24-Oct-05 22:22

Roger Stoltz

24-Oct-05 22:22

Cannot help you there since I'm not running VC7.
It might be interesting to try the server built with VC6 and run it with the client built with VC7 since as I understand it you don't know whether the error is caused by the server or the client.

BTW, is this problem linked with the problem you've described a few threads down[^]?

--
Roger

It's supposed to be hard, otherwise anybody could do it!

odiesback25-Oct-05 5:04

25-Oct-05 5:04

Somewhat linked.

I managed to get ahead with this:

I created a completely new server with different interface names
and new GUIDs under VC6.

I got it to work on my client's app as long as I make a call to
CoCreateInstance(). Also worked on my VC7 client.

The only thing (though I dont need to use) is that if I make a call
to the CF directly and the try to CreateInstance() it fails.

and it still doesnt work with wih _com_ptr_t<>.

Another curiosity:
Even though my server tlb and dll are registered and they work, when
I try to access the object using the OLE/COM View->All Objects it crashes
the utility program.

Other objects listed allow me to click on them and see the interfaces.
Not mine. but I am getting there little by little Smile | :)

Thanks again for your help

Odie

Roger Stoltz25-Oct-05 12:03

Roger Stoltz

25-Oct-05 12:03

odiesback wrote:
when
I try to access the object using the OLE/COM View->All Objects it crashes
the utility program.

This sounds like you have contaminated the registry with incorrect and/or obsolete information.
Does the viewer crash when you're expanding the leaf in the tree view, or does is crash when you select your server? Describe it some more.
Is it a new behaviour or has the viewer crashed whenever you've tried to browsing your COM servers?
However, it should be fairly certain that the error is connected to the server and not the client.

Try and search the registry for CLSID values, ProgIDs, TLIDs etc generated for your server(s).
First you may want to try to unregister your server and fire up the OLE/COM viewer again to verify that the "contaminating information" is still making the viewer crash. If not, then you know its in the information that gets registered with your current server.
Your first aim to shoot for would be not to crash the OLE/COM viewer while browsing/viewing your server and its type library.

--
Roger

It's supposed to be hard, otherwise anybody could do it!

odiesback25-Oct-05 13:46