Added class to invoke methods on dynamic COM IDispatch.

Core/InteropServices/SafeIDispatch.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Vanara.InteropServices
+{
+	/// <summary>Provide a IDispatch-based (e.g. late-bound) access to a COM object. Use <see cref="Invoke"/> to work with the object.</summary>
+	public class SafeIDispatch : ComReleaser<dynamic>
+	{
+		/// <summary>Initializes a new instance of the <see cref="SafeIDispatch"/> class.</summary>
+		/// <param name="target">The target object which must be a raw COM object.</param>
+		public SafeIDispatch(object target) : base(target)
+		{
+			if (!Marshal.IsComObject(target))
+				throw new ArgumentException("The target object must be a COM object");
+			RawPointer = GetRawPointer(target);
+		}
+
+		/// <summary>Gets the pointer to the IDispatch instance.</summary>
+		/// <value>A pointer to the IDispatch instance.</value>
+		public IntPtr RawPointer { get; }
+
+		/// <summary>Determines whether the specified <see cref="System.Object"/>, is equal to this instance.</summary>
+		/// <param name="other">The <see cref="System.Object"/> to compare with this instance.</param>
+		/// <returns><see langword="true"/> if the specified <see cref="System.Object"/> is equal to this instance; otherwise, <see langword="false"/>.</returns>
+		public bool Equals(ComReleaser<dynamic> other) => other?.Item is null || Item is null ? false : (bool)(RawPointer == GetRawPointer(other.Item));
+
+		/// <summary>Determines whether the specified <see cref="System.Object"/>, is equal to this instance.</summary>
+		/// <param name="obj">The <see cref="System.Object"/> to compare with this instance.</param>
+		/// <returns><see langword="true"/> if the specified <see cref="System.Object"/> is equal to this instance; otherwise, <see langword="false"/>.</returns>
+		public override bool Equals(object obj) => obj is ComReleaser<dynamic> o ? Equals(o) : base.Equals(obj);
+
+		/// <summary>Returns a hash code for this instance.</summary>
+		/// <returns>A hash code for this instance, suitable for use in hashing algorithms and data structures like a hash table.</returns>
+		public override int GetHashCode() => RawPointer.ToInt32();
+
+		/// <summary>
+		/// Method to encapsulate operations against the late-bound COM object. The caller must handle any exceptions that may result as part
+		/// of the operation.
+		/// </summary>
+		/// <param name="action">A method that performs work against the late-bound COM object.</param>
+		public void Invoke(Action<dynamic> action) => action.Invoke(Item);
+
+		private static IntPtr GetRawPointer(object target)
+		{
+			var result = IntPtr.Zero;
+			try
+			{
+				result = Marshal.GetIDispatchForObject(target);
+			}
+			finally
+			{
+				// Decrement reference count added by call to GetIDispatchForObject
+				if (result != IntPtr.Zero)
+					Marshal.Release(result);
+			}
+			return result;
+		}
+	}
+}