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Lim Bio Liong - Professional Profile



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Lim Bio Liong is a Specialist at a leading Software House in Singapore.

Bio has been in software development for over 10 years. He specialises in C/C++ programming and Windows software development.

Bio has also done device-driver development and enjoys low-level programming. Bio has recently picked up C# programming and has been researching in this area.

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GeneralRe: Question about IRpcChannelBuffer From MSDN COM Newsgroup Pin
Lim Bio Liong10-Nov-05 17:35
Lim Bio Liong10-Nov-05 17:35 
GeneralAbout Reference Counting Pin
Lim Bio Liong10-Nov-05 17:21
Lim Bio Liong10-Nov-05 17:21 
GeneralRe: About Reference Counting Pin
Lim Bio Liong10-Nov-05 17:22
Lim Bio Liong10-Nov-05 17:22 
GeneralHow to: Determine If a File Is an Assembly (C# Programming Guide) Pin
Lim Bio Liong27-Oct-05 4:44
Lim Bio Liong27-Oct-05 4:44 
GeneralATL Attributes (a.k.a. Embedded IDL). Pin
Lim Bio Liong21-Oct-05 22:19
Lim Bio Liong21-Oct-05 22:19 
GeneralBasic COM/.NET Interop Techniques Pin
Lim Bio Liong12-Oct-05 1:54
Lim Bio Liong12-Oct-05 1:54 
GeneralRe: Basic COM/.NET Interop Techniques Pin
Lim Bio Liong12-Oct-05 14:03
Lim Bio Liong12-Oct-05 14:03 
GeneralRe: Basic COM/.NET Interop Techniques Pin
Lim Bio Liong18-Oct-05 5:50
Lim Bio Liong18-Oct-05 5:50 
A Simple COM Object Interface

We begin our code development by defining a simple COM interface named ISimpleCOMObject. Using Visual Studio .NET, we create an ATL project named SimpleCOMObject.sln (complete source codes for this project is included in the downloadable sample codes).

This SimpleCOMObject.sln project will not contain any useful implementation codes. Its purpose is simply to allow us to automate the creation and maintenance of the ISimpleCOMObject interface. This is accomplished via the use of the ATL Wizards.

The project file folder also serves as the central point for the storage and generation of various .NET related resources (e.g. Primary Interop Assembly, Strong Name Key Files, etc). More on these later.

Listed below is a fragment of code taken from SimpleCOMObject.idl showing the ISimpleCOMObject interface :

[
object,
uuid(9EB07DC7-6807-4104-95FE-AD7672A87BD7),
dual,
nonextensible,
helpstring("ISimpleCOMObject Interface"),
pointer_default(unique)
]
interface ISimpleCOMObject : IDispatch{
[propget, id(1), helpstring("property LongProperty")] HRESULT LongProperty([out, retval] LONG* pVal);
[propput, id(1), helpstring("property LongProperty")] HRESULT LongProperty([in] LONG newVal);
[id(2), helpstring("method Method01")] HRESULT Method01([in] BSTR strMessage);
};

ISimpleCOMObject contains one property (LongProperty) and one method (Method01()). We stipulate that ISimpleCOMObject is meant to be implemented by an object that takes a long value (LongProperty) and then displays its value when we call Method01(). The BSTR parameter "strMessage" is meant to be a short message which is to be displayed with the LongProperty value when Method01() is called.

We defined ISimpleCOMObject as a dual interface. Hence a client application can call its methods by using a vtable interface pointer or by using an IDispatch interface pointer. Although it is possible to define ISimpleCOMObject as deriving from IUnknown, I have chosen to derive it from IDispatch in order to ensure that parameters and return values for its methods be strictly automation-compatible (i.e. the types that can be stored in a VARIANT structure). This is done to keep things simple.

I will assume that the reader is already well-versed in the implementation of a COM interface using an unmanaged language like C++. It is the implementation in a .NET language like C# that I intend to explain in detail in this article. The use of automation-compatible types will help to keep this process as simple as possible.

Although SimpleCOMObject.sln contains no useful implementation for ISimpleCOMObject, we will nevertheless need to compile it. Once this project is compiled successfully, two important files will be produced :

1. A Type Library (SimpleCOMObject.tlb).

2. A DLL (SimpleCOMObject.dll).

These will be created in the Debug directory of the project's containing folder. If you have downloaded my sample codes, and have not modified anything so far, these files will be stored in the following path :

<main folder>\SimpleCOMObject\interfaces\SimpleCOMObject\Debug

where is wherever you have copied the source codes zip file to.

The SimpleCOMObject.tlb will be used to produce something known as a Primary Interop Assembly. More on this in the next section.

The SimpleCOMObject.dll itself will contain the SimpleCOMObject.tlb (embedded as a binary resource). It is important as it will be registered (by the Visual Studio .NET IDE) as the Type Library for the coclasses and interfaces defined in SimpleCOMObject.idl.

This Type Library registration is done so that COM will know where to look for type information when it needs to perform marshalling for the interfaces defined in SimpleCOMObject.idl. This process is also known as Type Library Marshaling.


-- modified at 19:55 Tuesday 18th October, 2005
GeneralRe: Basic COM/.NET Interop Techniques Pin
Lim Bio Liong18-Oct-05 7:01
Lim Bio Liong18-Oct-05 7:01 
GeneralSome Interesting Information About Struct Alignment Pin
Lim Bio Liong28-Sep-05 2:50
Lim Bio Liong28-Sep-05 2:50 
GeneralIDispatch Property Setting Pin
Lim Bio Liong9-Aug-05 2:56
Lim Bio Liong9-Aug-05 2:56 
GeneralRe: IDispatch Property Setting Pin
Lim Bio Liong9-Aug-05 3:01
Lim Bio Liong9-Aug-05 3:01 
Generalhow to make MIDL not mangle enum names Pin
Lim Bio Liong8-Aug-05 3:48
Lim Bio Liong8-Aug-05 3:48 
GeneralInterface Shims Pin
Lim Bio Liong17-Jul-05 20:50
Lim Bio Liong17-Jul-05 20:50 
GeneralRe: Interface Shims Pin
Lim Bio Liong17-Jul-05 20:54
Lim Bio Liong17-Jul-05 20:54 
GeneralRe: Interface Shims Pin
Lim Bio Liong17-Jul-05 20:55
Lim Bio Liong17-Jul-05 20:55 
GeneralRe: Interface Shims Pin
Lim Bio Liong17-Jul-05 20:56
Lim Bio Liong17-Jul-05 20:56 
GeneralTake Note when adding a new ATL ActiveX Property Into the Property Map Pin
Lim Bio Liong15-Jul-05 20:28
Lim Bio Liong15-Jul-05 20:28 
GeneralUsing CComVariant and VarCmp Pin
Lim Bio Liong16-Apr-05 0:16
Lim Bio Liong16-Apr-05 0:16 
GeneralProperly Transferring Memory Objects In Method Calls. Pin
Lim Bio Liong7-Mar-05 2:00
Lim Bio Liong7-Mar-05 2:00 
GeneralInstantiating Member Data Which Are References Pin
Lim Bio Liong22-Feb-05 16:52
Lim Bio Liong22-Feb-05 16:52 
GeneralRegistry Location of Services and Device Drivers Pin
Lim Bio Liong31-Jan-05 20:07
Lim Bio Liong31-Jan-05 20:07 
GeneralNew Year @ CodeProject Pin
Lim Bio Liong31-Dec-04 17:05
Lim Bio Liong31-Dec-04 17:05 
GeneralRe: New Year @ CodeProject Pin
ThatsAlok1-Jan-06 23:42
ThatsAlok1-Jan-06 23:42 
GeneralAn Interesting Question From Microsoft's COM Newsgroup Pin
Lim Bio Liong30-Dec-04 22:17
Lim Bio Liong30-Dec-04 22:17 

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