Added `BeginEndEventContext` to call delegates on context entry and exit

Core/BeginEndEventContext.cs

@@ -0,0 +1,71 @@
+using System;
+
+namespace Vanara.PInvoke
+{
+	/// <summary>A disposable context for which a delegate is called at entry and exit.</summary>
+	/// <example>
+	/// This class can be used as follows:
+	/// <code>using (var ctx = new BeginEndEventContext(h =&gt; RegisterForEvents(out h), h =&gt; UnregisterForEvents(h)))
+	/// {
+	///     // Check to see if begin function succeeded
+	///     if (!ctx.BeginSucceeded)
+	///         return;
+	///
+	///     // Do some work
+	/// }
+	/// // End function has been called</code></example>
+	/// <seealso cref="System.IDisposable" />
+	public class BeginEndEventContext : IDisposable
+	{
+		private readonly Func<object, bool> end;
+		private bool disposedValue;
+		private object obj = null;
+
+		/// <summary>Initializes a new instance of the <see cref="BeginEndEventContext"/> class.</summary>
+		/// <param name="onBegin">The optional delegate to call when creating the context.</param>
+		/// <param name="onEnd">The optional delegate to call when the context is disposed or goes out of scope.</param>
+		public BeginEndEventContext(Func<bool> onBegin, Func<bool> onEnd = null) : this(onBegin is null ? null : o => onBegin(), onEnd is null ? null : o => onEnd())
+		{
+		}
+
+		/// <summary>Initializes a new instance of the <see cref="BeginEndEventContext"/> class.</summary>
+		/// <param name="onBegin">The optional delegate to call when creating the context.</param>
+		/// <param name="onEnd">The optional delegate to call when the context is disposed or goes out of scope.</param>
+		public BeginEndEventContext(Func<object, bool> onBegin = null, Func<object, bool> onEnd = null)
+		{
+			end = onEnd;
+			BeginSucceeded = onBegin?.Invoke(obj) ?? true;
+		}
+
+		/// <summary>Gets the return value of the <c>onBegin</c> delegate.</summary>
+		public bool BeginSucceeded { get; }
+
+		/// <summary>Gets the return value of the <c>onEnd</c> delegate.</summary>
+		public bool EndSucceeded { get; private set; }
+
+		/// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
+		public void Dispose()
+		{
+			Dispose(disposing: true);
+			GC.SuppressFinalize(this);
+		}
+
+		/// <summary>Releases unmanaged and managed resources.</summary>
+		/// <param name="disposing">
+		/// <see langword="true"/> to release both managed and unmanaged resources; <see langword="false"/> to release only unmanaged resources.
+		/// </param>
+		protected virtual void Dispose(bool disposing)
+		{
+			if (!disposedValue)
+			{
+				if (disposing)
+				{
+					EndSucceeded = end?.Invoke(obj) ?? true;
+				}
+
+				obj = null;
+				disposedValue = true;
+			}
+		}
+	}
+}