Add ContextSwitcher class.

PInvoke/Ole/Ole32/CtxtCall.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace Vanara.PInvoke
@@ -49,7 +50,12 @@ public interface IContextCallback
 			/// </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);
+			HRESULT ContextCallback(
+				[MarshalAs(UnmanagedType.FunctionPtr)] PFNCONTEXTCALL pfnCallback,
+				in ComCallData pParam,
+				in Guid riid,
+				int iMethod,
+				[In, Optional] IntPtr pUnk);
 		}
 
 		/// <summary/>
@@ -66,5 +72,30 @@ public struct ComCallData
 			/// <summary/>
 			public IntPtr pUserDefined;
 		}
+
+		/// <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
+		[ComImport, Guid("0000034e-0000-0000-C000-000000000046"), ClassInterface(ClassInterfaceType.None)]
+		public class ContextSwitcher : IContextCallback
+		{
+			/// <inheritdoc/>
+			[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
+			public virtual extern HRESULT ContextCallback(
+				[MarshalAs(UnmanagedType.FunctionPtr)] PFNCONTEXTCALL pfnCallback,
+				in ComCallData pParam,
+				in Guid riid,
+				int iMethod,
+				IntPtr pUnk = new IntPtr());
+		}
+
+		/// <summary>CLSID_ContextSwitcher</summary>
+		public static readonly Guid CLSID_ContextSwitcher = new Guid(0x0000034e, 0x0000, 0x0000, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46);
+
+		/// <summary>IID_IEnterActivityWithNoLock</summary>
+		public static readonly Guid IID_IEnterActivityWithNoLock = new Guid(0xd7174f82, 0x36b8, 0x4aa8, 0x80, 0x0a, 0xe9, 0x63, 0xab, 0x2d, 0xfa, 0xb9);
+
+		/// <summary>IID_ICallbackWithNoReentrancyToApplicationSTA</summary>
+		public static readonly Guid IID_ICallbackWithNoReentrancyToApplicationSTA = new Guid(0x0a299774, 0x3e4e, 0xfc42, 0x1d, 0x9d, 0x72, 0xce, 0xe1, 0x05, 0xca, 0x57);
 	}
 }

UnitTests/PInvoke/Ole/Ole32/Ole32Tests.cs

@@ -95,5 +95,12 @@ public void IPropSetStorageTest()
 				Assert.That(prvRead[0].Value, Is.EqualTo("VALUE"));
 			}
 		}
+
+		[Test]
+		public void ContextSwitcher()
+		{
+			Assert.AreEqual(CLSID_ContextSwitcher, typeof(ContextSwitcher).GUID);
+			IContextCallback contextCallback = new ContextSwitcher();
+		}
 	}
 }