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Hi everybody,
I'm a complete COM beginner and I'm wrestling with my first project using MSVC.
Using the ATL wizard I can successfully create a simple DLL (add simple ATL object, AddMethod).
My problem is how can I return a value from my method ? I DO NOT want to pass pointers, which I then manipulate within the method but I want to be able to return the value "directly" (retVal = obj.mymethod()). I'm sure this can be done, but it seems the return type of COM methods is always HRESULT !??
Can I do this using properties (AddProperty) ?
A few lines of example code would be great.
Many thanks,
Axel
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It is completely possible to create a COM interface function that returns the value directly like this:
DWORD GetCount();
However, I would only recommend doing this if you are only writing this object for use in your programs, and you will be using the object as an INPROC_SERVER.
If you want to write COM objects that are truely binary compatible, and can be used by other languages than C++, like VB, then you will need to alway return HRESULT. The reason why is for programs that perfrom network or interprocess communication through COM objects. Whenever you expand the boundaries of your program, there are certain situations that can occur that are out of your control, like the user disconnects their computer from the network. The other libraries that COM depends on will use the HRESULT to indicate this to your program or the program that is using your object.
If you do not use pointers to return values to the user, it becomes more difficult to marshal your data across process boundaries and computers.
Here is a simple prototype for a Get procedure:
HRESULT __stdcall GetCount(DWORD *dwCound);
You want to use the stdcall calling convention for all of your functions in COM, because this is the convention that all programs expect when dealing with a COM interface. _cdecl is the default for VC++.
The bool Essential COM,/i> by Don Box is very insightful for learning COM.
Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!
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If you want to get a retval from an ATL/COM function, you have to declare the variable that stores the retval as [out, retval] in the ATL Interface.
Example:
interface IExampleClass : IDispatch
{
[id(1), helpstring("Method ExampleFunc")] HRESULT ExampleFunc([in] int nParam1, [in] int nParam2, [out, retval] int* nRet);
}
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Hi
Iwant to develop service in which I need to create a thread.
How can I implement a thread in a service?.I am using ATL com Wizard to create the service.
Thanks
Pathi
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Dear all:
I made a Internet download component(such as a.cab).Then I execute the following command:
1.Makecert -sk test1 -r -ss test1
2.SignCode -s test1 a.cab
However the command output is:
"This file is signed,but not timestamped."
How can I make a timestamped digital certification.
Could you give me some advice.
thanks a lot.
liuage
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-t http://timestamp.verisign.net/scripts/timstamp.dll
Todd Smith
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Is there a class just as MFC's CTime in ATL/WTL?i am waitin for you answer!
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I exercise the pure c++(No supported by MFC and ATL,even IDisptch interface) to write:
1.proxy/stub DLL;
2.out proc server EXE;
3.client EXE.
Then I run the program.When the client call function of connectable object in the server through interface,
All work well;But if the server call function of the sink in the client even like QueryInterface(.....) ,
A strange thing raises.For example,I test the command below:
//the pUnk is passed from client by Advise(......)
HRESULT hResult=pUnk->QueryInterface(IID_IUnknown,(void**)(&pIUnknown))；
Now I make use of FormatMessage(.....) to check the value of hResult,
the string is "The operation completed successfully";
Whereas QueryInterface(.....) does not implement!(I add MessageBox(....) topside to prompt me),
I want to known the reason,who can help me?thanks a lot!
//A slice of my source code
//MyCom.idl
import "unknwn.idl" ;
import "OCIDL.IDL" ;
//IMyEventSink interface,CMyEventSink object do the realization
[
object,
uuid(5A76E364-92E6-4d90-B575-31C0497FD174),
helpstring("IMyEventSink Interface"),
pointer_default(unique)
]
interface IMyEventSink : IUnknown
{
HRESULT Test([in] DWORD dwShowNum) ;
};
//the rest omits
..............
C/C++ code fans
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The problem had been resolved,I forgot to call QueryInterface(...)in the Advise(...),It is said in MSDN that calling the function is necessary!
Thank all of you! 
C/C++ code fans
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My application is created using MFC / VC6.0. I host a webbrowser control within my dialog. When I display a HTML page within the control & click on the url links I have provided, I'm able to capture them in BeforeNavigate2 event successfully. This I use it to display different functionality when I'm offline. But I have a problem when I host Flash Ads within my WebBrowser.
How can I trap the events like clicking on a hyperlink provided in Flash Ad & communicate it back to my application.I do know there are events like OnMouseup, OnMouseDown etc in Flash. I'm more particularly interested in my application intercepting the clicked event of the Flash, processing & redirecting it back to be opened up in the browser control
anandhi
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i want to use WRL::CString ,but once i add #include <atlmisc.h> to the stdafx.h,the compiler will notify me with the following:
error C2664: '_LoadString' : cannot convert parameter 2 from 'class WTL::CString' to 'char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
Error executing cl.exe.
who can help me?
i am coming quietly just as i am leaving quietly.
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Try explicitly casting the CString variable (Parameter 2 of the LoadString function that is failing) to a LPCTSTR. This should for the compiler to use the cast operator that is declared for the WTL::CString.
Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!
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I created a object and used it in ASP. All the things were fine for the first time. But after that I found when I built the com again, it report that LINK : fatal error LNK1104: cannot open file "Debug/StudentManager.dll".
I thought it because StudentManager.dll is still used by asp. But when I close asp or even logoff the computer, it didn't work yet. I can not use Release method in ASP as in client program to release object.
So if anyone has such experience, please tell me.
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Yet another wonder of some Win32 components. It's most probably still locked by some other "component" such as the Transaction Manager or the ... You get the picture. You're basically left to wait until some timeout of some "nice" service that holds this interface for you, in case you'd need it again, is released.
Another way to fix it is to use plain RPC or CORBA.
Microsoft=sh*t? No. Not always, but often.
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what are good books for learning atl ?
i've got "beginning atl com programming" by Gimes Stockton Reily and Templeton
but its pretty much unreadble
any suggestions?
bryce
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By my experiences, if you want to understand ATL,you must had known COM first.
Otherwise, you will get into troubles. 
After you readed COM,I think the book 'ATL Internals' is a good choice for you.
tomPeakz
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yer ive got a pretty good handle on com
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I would agree, for you to completely understand ATL, you really must understand what it is trying to do for you. Some of the terminology can be confusing, but if you become comfortable with COM, you will go a lot farther.
For COM books, I would recommend Don Box's Essential COM for concepts and theory, and I would get one other book if you like to work from examples. I don't really have a book to suggest for this, I just use the examples from MSDN.
Then like TomPeakz said, I would recommend Rector and Sells ATL Internals when you feel that you are ready for ATL. This is the only book on ATL that I own, but it has been more than enough for me for the 3 years that I have been using ATL.
Good Luck
Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!
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I'm programming on outlook com addin,I want to add a new "Folder" to the
"Folders List" like public
folder and Email Folder. Not the subfolder in the Email Folder.
But I could not found any methods to do this .Some one told me that I
must
write a new outlook service adding to the outlook,I think that is. So I
searched all of the documents
like MSDN...,but found nothing relative toptics.Does anybody know that ? (I use VC++)
Good Luck!
Tom Peakz
tomPeakz
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I created a MFC project. It was used to process bitmaps. I used embedded bitmap object and use mspaint.exe as server to edit bitmap. When I created a new object, it can work well. But I want to open an existed bmp file, I don't know how to change the object's content. Would anyone like to help me?
Thank you all very much! 
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Greetings,
I was wondering if there was a way to have an windowless ActiveX control refresh itself within IE?
I am trying to have an image draw in an ATL activeX control, and cycle through the different dib images periodically, and not have to refresh the browser for the new image.
I tried using "IOleInPlaceObjectWindowlessImpl" but every hdc, and rect comes back invalid from the call.
I assume that it has something to do with the container (IE) not allowing such things, but since I am
very new to ActiveX development I can't be sure.
Thanks in advance to anyone who knows a solution! (Hopefully)
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Greetings to all,
I did find a solution to my problem.
For some reason using the internet explorer as my container did not provide a windows handle to itself
that is why I was getting a windowless control.
So I created an activex control, and added an ATL object "full control" based on a static control.
I overwrote the WM_Paint for the static control, and now I can update the window at any time I want using
a timer.
Now life is good!
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Problem: Not able to run ActiveMovie3 OCX in worker thread.
My code is As follows:
1) I have declared pointer variable for ActiveMovie3 as class level
2) I have created Activemovie3 instance in OnInitdialog()
Code:
OnInitDialog()
{
CWnd *desk=GetDesktopWindow();
CRect rect;
desk->GetWindowRect(&rect);
m_Mplayer=new CActiveMovie3;
m_Mplayer->Create("Mediaplayer",WS_CHILD,rect,this,2222);
CwinThread *movieThread=AfxBeginThread(Mediathread,m_MPlayer);
Return TRUE;
}
UINT Mediathread(LPVOID pvoid)
{
CActiveMovie3 *m_MPlayer1=(CActiveMovie3*)pvoid;
int i=0;
while(true)
{
if(i++%2==0)
{
m_MPlayer1->SetAutoStart(TRUE);
m_MPlayer1->SetFileName("E:\\Boys.avi");
}
else
{
m_MPlayer1->SetFileName("E:\\Boys.avi");
}
Sleep(120000);
if(i>5)
break;
}
return 0;
}
Same code is working fine with the timer.
My timer code is as follows:
OnTimer(UINT nIDEvent)
{
static int i=0;
if(i++%2==0)
{
m_MPlayer->SetAutoStart(TRUE);
m_MPlayer->SetFileName("E:\\Aa.mpa");
}
else
{
m_MPlayer->SetFileName("E:\\Boys.avi");
}
CDialog::OnTimer(nIDEvent);
}
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You may consider calling CoInitialize() in the new thread to join a STA apartment. Also, you seem to create an object in main STA (in OnInitDialog) and then pass a raw interface pointer to in (wrapped with CActiveMovie3) to another apartment. It violates COM principles.
Consider using CoMarshalInterThreadInterfaceInStream or create an object in Mediathread.
-= Alexander =-
<<= Long Live COM =>>
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Hello,
I am looking at converting some C++ code to use COM objects instead to avoid recomiling the world when anything changes.
At the moment I am trying to work out whether you can have a static method/property in an interface (equivalent to static function in a C++ class).
None of the documentation/books I have seen even mentions this, I am therefore presuming it is something that isn't possible.
If anyone could confirm this, or maybe point out some 'alternatives' to me I would be grateful.
Also, is it possible to publish a non-implemented interface for use by third parties in cases where I have defined some 'pure-virtual' methods - would this be distributed as a type library???
Thanks
Paul.
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