• General considerations
• Creating COM servers (ActiveX servers) is relative simple in Power++, just use the corresponding target type.
• As default it always creates a interface named <Target>Ctl, if you wish to rename this, then you have to open the corresponding <Target>.wxf file and replace all occurances of the <Target>Ctl string with simply <Target>. Then rename the <Target>Ctl.wxt file into <Target>.wxt.
• In the interface definitions, you can specify multiple Methods with the same name, but different parameterlists. You can build this COM DLL sucessfully, but unfortunally you won't be able to use it. It is simply not supported, so you have to give all methods a unique name.
• When invoking methods of COM servers, either the com subsystem or the com server itself can generate exceptions. If this happens, a popup dialog informs you about this and waits for a click on the OK button. You can disable this behaviour with the following code:
  WOleApplicationObject *appObject = WOleApplicationObject::GetOleApplicationObject( );
if (appObject)
{
#ifndef _DEBUG
appObject->SetShowAutomationErrors(false);
#endif
}
  This must be disabled for every thread who calls com objects, since this setting is per thread. So if you build a ISAPI extension DLL who in turn calls COM servers, don't forget to add the code above in each ProcessRequest method, since the webserver is multithreaded.
  The check if the appObject not beeing NULL is required, since it may sometimes occur that the GetOleApplicationObject does not return anything usefull. Until now I have not found any rules for this behaviour.

• Errormessages when building a COM server	Cause
  Missing end of function	The ; is missing after the functiondefinition
  Unexpected word	The ; is missing after the functiondefinition
  Unrecognised type specifier in parameter/return value	You try to use a unsupported type as methodparameter. (*)
  Invalid type	You try to use a unsupported type as methodparameter. (*)

• According to the onlinehelp only the following types can be specified in the parameterlist.
• WByte // a single byte unsigned char
• WShort // short
• WInt // int
• WUInt // unsigned int
• WLong // long
• WULong // unsigned long
• WDouble // double
• WFloat // float
• WChar // You can also use the WChar data type, which represents a single character. WChar is defined to allow for multibyte character sets: character sets where some characters may be longer than a single byte. (Multibyte characters are required to support written languages which have a large number of characters in their alphabets.) WChar also allows for Unicode characters and double-byte characters. Unicode is used heavily by the OLE facilities.
• WBStr // represents a Visual Basic string type. You must use the WBStr to pass and return arguments, but it is not convenient to manipulate its string data directly. You should use the WString, WBuffer and WBString types to manipulate strings in your methods. When you want to return a string, you simply convert it to a WBStr and return the WBStr. For simpler handling of all the WBString/WBStr and WString conversions, you should use the WAXString class library.
• WHRESULT // is the same as the Windows type HRESULT. It is a 32-bit value that allows you to specify whether a method fails, and if so how it fails. Any result code that begins with S_ indicates that the method succeeded. Result codes starting with E_ indicate failure.
• WPIDispatch // represents a pointer to an IDispatch interface. IDispatch is the parent class of all automation interfaces, including the interfaces that you create with Power++.
• WPIUnknown // represents a pointer to an IUnknown interface. IUnknown is the parent class of all COM interfaces.
• WVARIANT_BOOL // data type represents a Boolean value. You can use the standard TRUE and FALSE constants as you would with the WBool class. Strictly speaking, the value of true for the WVARIANT_BOOL is defined to be -1 (negative one) and the value of false is 0 (zero). However, any non-zero value is taken to be true in practice, and zero is taken to be false.

Special infos about parameters.

You can pass COM servers as parameters to other com objects. To allow this, the called method must have a parameter of type WPIUnknown.

In P++ you can invoke such a method with the following sequence:

WOleProgrammableObject *_myServer;
WOleProgrammableObject *_myObject;
_myServer= new COMServer;
_myServer->Create(); // This is important, otherwise all methode calls will fail for no aparent reason.
_myObject= new COMParameter;
_myObject->Create(); // This is important, otherwise all methode calls will fail for no aparent reason.

WPIDispatch wpiParam= (WPIDispatch )*_myObject;
WVariant wvParam(wpiParam);
retVal= _myServer->CallMethod(&wvParam);
errorInfo = _myServer->GetErrorInfo();
if (errorInfo.error != WInvokeError_None)
{
// Handle errorcondition
}

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