1	Using COM Objects From .NET Framework Applications
2	Overview How to use COM objects from .NET The CLR’s support for COM and COM+ The cost of using COM objects from .NET
3	Using COM Types From .NET Obtain a managed definition of the COM types Primary Interop Assembly Standard managed definition First choice when available Create your own (if necessary) By adding references to the type library within Visual Studio By using type library importer (TlbImp) By defining types manually
4	Using COM Types From .NET Reference the Interop Assembly when building projects Done for you when adding reference in VS Use /r: from command line compilers CSC /t:library /r:MyLib.dll MyCode.cs Use the types as managed types Create instances with new Catch exceptions Even extend them
5	Data Type Conversion Performed at Import DATE System.DateTime BSTR System.String SafeArray(int) int[] interface IFoo interface IFoo coclass Bar class BarClass + interface Bar CURRENCY System.Decimal VARIANT System.Object IEnumVariant IEnumerator
6	Imported Signature Translation COM Method Signature HRESULT FormatDate(BSTR s, DATE d, [out, retval] int *retval); int FormatDate(String s, DateTime d); .NET Method Signature
7	Model Transparency Don’t think of types as COM types No reference counting, No IDispatch No HRESULTs. No GUIDs Sink events using managed eventing model Cast to specific interfaces as necessary InvalidCastException if QI fails Failure HRESULTs are automatically mapped to exceptions
8	.Net to COM Object Support Calling COM Components
9	Sample Code public static void Main() { try { Excel.Application app = new Excel.Application(); app.Workbooks.Add( Excel.XlWBATemplate.xlWBATWorksheet); app.Visible = true; app.UserControl = true; } catch (Exception) { Console.WriteLine("Error creating excel application!"); } }
10	Installing Interop Assemblies PIA should be provided by TLB publisher whenever possible Interop Assemblies must be resolvable at runtime Installed in Global Assembly Cache Signed using TlbImp TLBIMP MyLib.tlb keyfile:MyKey.snk Installed in the GAC using GACUTIL /i:MyLib.dll Installed in Application directory Copied to app directory
11	Late binding To COM Objects No Import Required public static void Main() { String progId = “Word.Application”; Type t = Type.GetTypeFromProgID(progId); Object o = Activator.CreateInstance(t); t.InvokeMember("Visible", BindingFlags.SetProperty \| BindingFlags.Public \| BindingFlags.Instance, null, o, new Object[] {true}); }
12	Late binding To COM Objects From Visual Basic .NET Public Shared Sub Main Dim word As Object word = CreateObject("Word.Application") word.Visible = true End Sub
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14	Beyond The Basics Output of TlbImp works without modifications for most type libraries TlbImp has limitations Success HRESULTs C-Style arrays Passing null to byref or out parameters HRESULT Meth([out] int *pInt); Multi dimensional SAFEARRAYs Non-zero based SAFEARRAYs
15	Customizing Tlbimp Output Command line options /sysarray /namespace /asmversion Using ILDasm/ILAsm 1. tlbimp foo.tlb 2. ildasm foo.dll /out:foo.il 3. Edit the MSIL as required. 4. ilasm foo.il
16	Sample Preserve Signature
17	Defining COM Types Manually Sometimes you need more control Methods with complicated structures as arguments Large TLB – only using a few classes No type library Parameter and return value marshalling HRESULT behavior
18	Defining COM Types Manually
19	Primary Interop Assemblies Standard managed definition of a COM type library Should be provided by the vendor of the COM component Must be strongly named /primary tlbimp command line option Are registered using regasm
20	GC Considerations GC sees COM objects as smaller than they really are GC isn’t aware of the unmanaged memory of the COM object Use Marshal.ReleaseComObject to force the release of a COM object Forcing the release can be required for some COM object models
21	Performance Considerations Use STA threads to talk to STA components Transitions have overhead PInvoke: Roughly 10 instruction per call COM Interop: Roughly 50 instruction per call Data marshaling adds overhead Depending on type and size of data Blittable types are cheap Use caching to avoid chatty calls Consider rewriting existing code
22	Performance
23	Summary It is really easy to use COM components from .NET Any and all COM components can be used from .NET For real world applications, Interop performance is quite good
24	Questions