MSDN Magazine - January 2009 - (Page 23)

COM RCW IDispatch GetTypeInfoCount GetTypeInfo TYPEATTR general info cFuncs cVars climpleTypes counts FUNDESC invkind ELEMDESC info about a parameter paramdesc.wParamFlags ags (ByVal/ByRef &c.) elemDesc.tdesc itstype ITypeInfo information about a class or interface GetDocumentation GetNames to get the name of this type to get the name of a member info about a function member what kind of function its parameters its return type GetTypeAttr ReleaseTypeAttr GetFuncDesc ReleaseFuncDesc GetVarDesc ReleaseVarDesc GetRefTypeOfImpIType GetImpITypeFlags Invoke to invoke a given function member lprgelemdescParam elemdescFunc VARDESC info about a eld member TYPEDESC elemdescVar its type a type, for example String Array Integer ByRef IUnknown Figure 4 ITypeInfo and Type Information anywhere in the .NET Framework, so you have to define it yourself, as you see in Figure 5. I left the function GetIDsOfNames empty because it’s not needed for the current purposes; you’ll need to in clude an entry for it, though, because the interface has to list the right number of methods in the right order. You might wonder why IDispatch has its InterfaceType attri bute set to ComInterfaceType.InterfaceIsUnknown rather than set to ComInterfaceType.InterfaceIsIDisapatch. That’s because the InterfaceType attribute says what the interface inherits from, not what it is. You have an ITypeInfo. Now it’s time to start reading from it. Take a look at Figure 6 because the function I’m going to implement to dump the type information is shown there. For GetDocumentation, Figure 5 Defining the IDispatch Interface ''' ''' IDispatch: this is a managed version of the IDispatch interface ''' ''' We don't use GetIDsOfNames or Invoke, and so haven't ''' bothered with correct signatures for them. _ Interface IDispatch Sub GetTypeInfoCount(ByRef pctinfo As UInteger) Sub GetTypeInfo(ByVal itinfo As UInteger, ByVal lcid _ As UInteger, ByRef pptinfo As IntPtr) Sub stub_GetIDsOfNames() Sub Invoke(ByVal dispIdMember As Integer, ByRef riid As Guid, _ ByVal lcid As UInteger, ByVal dwFlags As UShort, _ ByRef pDispParams As ComTypes.DISPPARAMS, _ ByRef pVarResult As [VARIANT], ByRef pExcepInfo As IntPtr, _ ByRef pArgErr As UInteger) End Interface the first parameter is a MEMBERID, that is, GetDocumentation is meant to return information about each member of the type. But you can also pass in MEMBERID_NIL, which has the value 1, to get information about the type itself. Note how the marshaling works. When you call typeInfo.Get TypeAttr, it allocates an unmanaged block of memory and returns to you the pointer pTypeAttr. Then Marshal.PtrToStructure cop ies from this unmanaged block into a managed block (which will then be garbage collected). So it’s fine to immediately call type Info.ReleaseTypeAttr. As shown previously, you need typeAttr to know how many members and implemented interfaces there are (typeAttr.cFuncs, typeAttr.cVars, and typeAttr.cImplTypes). Figure 6 DumpTypeInfo ''' ''' ''' ''' Sub DumpType: prints information about an ITypeInfo type to the console the type to dump DumpTypeInfo(ByVal typeInfo As ComTypes.ITypeInfo) ' Name: Dim typeName = "" : typeInfo.GetDocumentation(-1, typeName, "", 0, "") Console.WriteLine("TYPE {0}", typeName) ' TypeAttr: contains general information about the type Dim pTypeAttr As IntPtr : typeInfo.GetTypeAttr(pTypeAttr) Dim typeAttr = CType(Marshal.PtrToStructure(pTypeAttr, _ GetType(ComTypes.TYPEATTR)), ComTypes.TYPEATTR) typeInfo.ReleaseTypeAttr(pTypeAttr) End Sub msdnmagazine.com January 2009 23 http://www.msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2009

Toolbox CLR Inside Out Basic Instincts Cutting Edge Test Run First Look� Geneva Framework Silverlight Windows Mobile Service Station Security Briefs Extreme ASP.NET Foundations .NET Matters { End Bracket }

MSDN Magazine - January 2009

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