Added IContextCallback (#209)

PInvoke/Ole/Ole32/CtxtCall.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Vanara.PInvoke
+{
+	public static partial class Ole32
+	{
+		/// <summary>
+		/// The function to be called inside the object context if <see cref="IContextCallback.ContextCallback(PFNCONTEXTCALL, in
+		/// ComCallData, in Guid, int, IntPtr)"/>.
+		/// </summary>
+		/// <param name="data">The data passed to the function when it is called in the context.</param>
+		/// <returns>The result. Typically the result of <see cref="CoDisconnectContext(uint)"/>.</returns>
+		[UnmanagedFunctionPointer(CallingConvention.Winapi)]
+		[PInvokeData("ctxtcall.h", MSDNShortId = "NN:ctxtcall.IContextCallback")]
+		public delegate HRESULT PFNCONTEXTCALL(in ComCallData data);
+
+		/// <summary>Provides a mechanism to execute a function inside a specific COM+ object context.</summary>
+		/// <remarks>An instance of this interface for the current context can be obtained using CoGetObjectContext.</remarks>
+		// https://docs.microsoft.com/en-us/windows/win32/api/ctxtcall/nn-ctxtcall-icontextcallback
+		[PInvokeData("ctxtcall.h", MSDNShortId = "NN:ctxtcall.IContextCallback")]
+		[ComImport, Guid("000001da-0000-0000-C000-000000000046"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+		public interface IContextCallback
+		{
+			/// <summary>Enters the object context, executes the specified function, and returns.</summary>
+			/// <param name="pfnCallback">The function to be called inside the object context.</param>
+			/// <param name="pParam">The data to be passed to the function when it is called in the context.</param>
+			/// <param name="riid">The IID of the call that is being simulated. See Remarks for more information.</param>
+			/// <param name="iMethod">The method number of the call that is being simulated. See Remarks for more information.</param>
+			/// <param name="pUnk">This parameter is reserved and must be <c>NULL</c>.</param>
+			/// <returns>
+			/// This method can return the standard return values E_INVALIDARG, E_OUTOFMEMORY, E_UNEXPECTED, and E_FAIL. If none of these
+			/// failures occur, the return value of this function is the <c>HRESULT</c> value returned by the pfnCallback function.
+			/// </returns>
+			/// <remarks>
+			/// <para>
+			/// This method simulates a method call on an object inside the context. It is intended for low-level operations, such as
+			/// cleanup/lazy marshaling, that respect the application's reentrancy expectations.
+			/// </para>
+			/// <para>
+			/// To give the infrastructure information, an interface and method number must be specified. The parameter riid must not be
+			/// IID_IUnknown, and the method number must not be less than 3.
+			/// </para>
+			/// <para>If riid is set to IID_IEnterActivityWithNoLock, the function is executed without an activity lock.</para>
+			/// <para>
+			/// If riid is set to IID_ICallbackWithNoReentrancyToApplicationSTA, the function does not reenter an ASTA arbitrarily. Most
+			/// apps should set riid to this values for general purpose use.
+			/// </para>
+			/// </remarks>
+			// https://docs.microsoft.com/en-us/windows/win32/api/ctxtcall/nf-ctxtcall-icontextcallback-contextcallback
+			[PreserveSig]
+			HRESULT ContextCallback(PFNCONTEXTCALL pfnCallback, in ComCallData pParam, in Guid riid, int iMethod, [In, Optional] IntPtr pUnk);
+		}
+
+		/// <summary/>
+		[PInvokeData("ctxtcall.h", MSDNShortId = "NN:ctxtcall.IContextCallback")]
+		[StructLayout(LayoutKind.Sequential)]
+		public struct ComCallData
+		{
+			/// <summary/>
+			public int dwDispid;
+
+			/// <summary/>
+			public int dwReserved;
+
+			/// <summary/>
+			public IntPtr pUserDefined;
+		}
+	}
+}