add OfType<T> extension method to IList

MBS.Framework/Collections/Generic/ExtensionMethods.cs

@@ -0,0 +1,58 @@
+//
+//  ExtensionMethods.cs - implements generic-typed extension methods for System.Collections classes
+//
+//  Author:
+//       Michael Becker <alcexhim@gmail.com>
+//
+//  Copyright (c) 2020 Mike Becker's Software
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+using System;
+using System.Collections.Generic;
+
+namespace MBS.Framework.Collections.Generic
+{
+	public static class ExtensionMethods
+	{
+		private static Dictionary<System.Collections.IList, Dictionary<Type, System.Collections.IList>> cacheOfT = new Dictionary<System.Collections.IList, Dictionary<Type, System.Collections.IList>>();
+		/// <summary>
+		/// Returns an array of type <typeparamref name="T" /> which consists of all elements in the specified <see cref="System.Collections.IList" /> that are of type
+		/// <typeparamref name="T" />.
+		/// </summary>
+		/// <returns>An array of type <typeparamref name="T" /> which consists of all elements in the specified <see cref="System.Collections.IList" /> that are of type
+		/// <typeparamref name="T" />.</returns>
+		/// <param name="obj">A <see cref="System.Collections.IList" /> containing the elements to search.</param>
+		/// <typeparam name="T">A type parameter indicating the type of elements to retrieve.</typeparam>
+		public static T[] OfType<T>(this System.Collections.IList obj)
+		{
+			if (!cacheOfT.ContainsKey(obj))
+			{
+				cacheOfT[obj] = new Dictionary<Type, System.Collections.IList>();
+			}
+			if (!cacheOfT[obj].ContainsKey(typeof(T)))
+			{
+				List<T> list = new List<T>();
+				for (int i = 0; i < obj.Count; i++)
+				{
+					if (obj[i] is T)
+					{
+						list.Add((T)obj[i]);
+					}
+				}
+				cacheOfT[obj][typeof(T)] = list;
+			}
+			return ((List<T>)(cacheOfT[obj][typeof(T)])).ToArray();
+		}
+	}
+}

MBS.Framework/MBS.Framework.csproj

@@ -86,6 +86,7 @@
     <Compile Include="CommandItem.cs" />
     <Compile Include="StockType.cs" />
     <Compile Include="ContextChangedEvent.cs" />
+    <Compile Include="Collections\Generic\ExtensionMethods.cs" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Logic\" />