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Read/write to native memory (also - Byte/ Int16/ Int64) StructureToPtr() PtrToStructure() DestroyStructure()
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Manage COM native memory (as pointed to by IntPtr) We found the following methods as useful for this: AllocCoTaskMem() FreeCoTaskMem() SizeOf()
#KEPSERVEREX 80070005 CODE#
Managed marshaling code makes use of the framework services provided in the namespace, especially the Marshal class. So the wrapper must reconstruct the information we lost. But more important, this wrapper now has to do all the custom marshaling, e.g. To use the interfaces we declared as above, it is recommended to write some wrapper classes. InterfaceType( ComInterfaceType.InterfaceIsIUnknown )] Let's look at a sample method (from an OPC custom interface IDL): We found there's often no way around the use of the special IntPtr type. Note this can be a very time consuming work! every method of all interfaces have to be coded in C#, and the critical (custom) parameters must be declared completely different. We have to rewrite our custom IDL file in a managed language code, here C#. Or the way we used, write a marshaling helper class (in C#).Currently, we must use one of two different workarounds:
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One first solution would be to edit the assembly produced by TLBIMP (using ILDASM), and replace ref int with int, and then compile IL back again with ILASM.īut if we look at some very custom IDL files, we also find methods with parameters like foo( int **arraybyref ) where arrays are passed by reference (caller allocates the memory)! Hand editing IL code won't work here, there's no marshaling signature for this. NET Beta2, there's unfortunately no tool (like 'IDLIMP') to import custom interface IDL files.Įxample: Since the MIDL compiler does not propagate size_is information to the type library, the marshaler doesn't know an array length and translates int to ref int. So if we compile a custom-interface IDL file, the generated TLB misses very important type descriptions, especially the method call parameter size (e.g. The problem is now, type libraries can only contain automation compliant information. the library generated by MIDL-compiler, named *.TLB). NET relies on the information found in a type-library for every imported COM component (e.g. NET framework, we must first analyze, why automation components can be used immediately.
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To understand the issues with COM custom interfaces and the. NET, or with the TLBIMP tool), pure custom COM interfaces will not work. While automation compliant COM objects will be nicely imported (as referenced COM objects inside Visual Studio. NET Framework will provide some interoperability layers and tools to reuse a large part of the existing COM/ActiveX/OCX components, but with some strong limitations.
#KEPSERVEREX 80070005 HOW TO#
We will show you in this article how to access OPC servers with custom interfaces and how to write an OPC client in. For some reasons and applications, it is preferable to use the custom interface directly. First, as a collection of COM custom interfaces, and secondly as COM-automation compliant components/wrappers. The OPC standard is defined at 'two different layers' of COM/DCOM. In industrial automation, OPC (OLE for Process Control, see is the primary COM component interface used to connect devices from different manufactures.