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Thursday 7 June 2012

COM INTEROPERABILITY in .Net


COM Interoperabillity


COM à Reusable

COM à written in one language (c++) and consumed by other language (VB)

COM has Metadata : stores all info stored inside type library like name, Id of interface, methods and argumetns.

COM is Not Extensible à drawback

COM   Issues
    METADATA       à Type Library – TLB 
      FREEING MEMORY  à Com relies on Ref. Count, .Net  on GC
            IUnknown interface required to be implemented by every com obj.
              AddRef(), Release() for destruction of object

INTERFACE à IUnknown, IDispatch,ICollectionEvent

METHOD BINDING- .Net uses Reflection, Com uses IDispatch

DATA TYPES à Variant type   , .Net class has Object

REGISTRATION à CLSID – 128 bit, ProgID (Excel.Application)

THREADING   à STA and MTA

ERROR HANDLING à HResult , .Net uses Exception

MARSHALLING à  COMà SafeArray  à Array  in .net             Variant in COM  à object in .net     BStr  à String  , IUnknown,IDispatch  à Object





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