From a391f0c18373cdead49cf1c4c0658076e87c8a91 Mon Sep 17 00:00:00 2001
From: dahall <dahall@byu.net>
Date: Thu, 9 Jun 2022 22:32:26 -0600
Subject: [PATCH] More work on ShellFolderCategorizer

---
 UnitTests/Windows.Shell/ShellFolderTests.cs                 | 10 ++++++++++
 Windows.Shell.Common/ShellObjects/ShellFolder.cs            |  3 ++-
 Windows.Shell.Common/ShellObjects/ShellFolderCategorizer.cs | 13 +++++++++----
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/UnitTests/Windows.Shell/ShellFolderTests.cs b/UnitTests/Windows.Shell/ShellFolderTests.cs
index a7d8c012..0d57bb3e 100644
--- a/UnitTests/Windows.Shell/ShellFolderTests.cs
+++ b/UnitTests/Windows.Shell/ShellFolderTests.cs
@@ -137,5 +137,15 @@ namespace Vanara.Windows.Shell.Tests
 			Assert.That(() => f.GetChildrenUIObjects<IShellLibrary>(default, i), Throws.TypeOf<NotImplementedException>());
 			Assert.That(() => f.GetViewObject<IShellLibrary>(default), Throws.TypeOf<InvalidCastException>());
 		}
+
+		[Test]
+		public void CategoryTest()
+		{
+			using var ie = new ShellFolder(KNOWNFOLDERID.FOLDERID_Documents);
+			Assert.That(ie.Categories, Is.Not.Empty);
+			Assert.That(ie.Categories.DefaultCategory?.Name, Is.Not.Null);
+			foreach (var c in ie.Categories)
+				TestContext.WriteLine($"{c.Name}");
+		}
 	}
 }
\ No newline at end of file
diff --git a/Windows.Shell.Common/ShellObjects/ShellFolder.cs b/Windows.Shell.Common/ShellObjects/ShellFolder.cs
index e6418bd3..2107968b 100644
--- a/Windows.Shell.Common/ShellObjects/ShellFolder.cs
+++ b/Windows.Shell.Common/ShellObjects/ShellFolder.cs
@@ -56,6 +56,7 @@ namespace Vanara.Windows.Shell
 	public class ShellFolder : ShellItem, IEnumerable<ShellItem>
 	{
 		internal IShellFolder iShellFolder;
+		private ShellFolderCategorizer categories;
 		private static ShellFolder desktop;
 
 		/// <summary>Initializes a new instance of the <see cref="ShellItem"/> class.</summary>
@@ -177,7 +178,7 @@ namespace Vanara.Windows.Shell
 
 		/// <summary>Gets the registered categorizers.</summary>
 		/// <value>The categorizers.</value>
-		public ShellFolderCategorizer Categories => new(IShellFolder);
+		public ShellFolderCategorizer Categories => categories ??= new(IShellFolder);
 
 		/// <summary>
 		/// Enumerates all children of this item. If this item is not a folder/container, this method will return an empty enumeration.
diff --git a/Windows.Shell.Common/ShellObjects/ShellFolderCategorizer.cs b/Windows.Shell.Common/ShellObjects/ShellFolderCategorizer.cs
index bcca0cc7..4377c43c 100644
--- a/Windows.Shell.Common/ShellObjects/ShellFolderCategorizer.cs
+++ b/Windows.Shell.Common/ShellObjects/ShellFolderCategorizer.cs
@@ -21,8 +21,12 @@ public class ShellFolderCategorizer : IEnumerable<ShellFolderCategory>
 	{
 		get
 		{
-			ICategoryProvider.GetDefaultCategory(out var guid, out _).ThrowIfFailed();
-			return GetCat(guid);
+			var hr = ICategoryProvider.GetDefaultCategory(out var guid, out _);
+			if (hr == HRESULT.S_OK)
+				return GetCat(guid);
+			if (hr == HRESULT.S_FALSE)
+				return null;
+			throw hr.GetException();
 		}
 	}
 
@@ -43,8 +47,9 @@ public class ShellFolderCategorizer : IEnumerable<ShellFolderCategory>
 	/// <inheritdoc/>
 	public IEnumerator<ShellFolderCategory> GetEnumerator()
 	{
-		ICategoryProvider.EnumCategories(out IEnumGUID penum).ThrowIfFailed();
-		return new IEnumFromCom<Guid>(penum.Next, penum.Reset).Select(g => GetCat(g)).GetEnumerator();
+		if (ICategoryProvider.EnumCategories(out IEnumGUID penum) == HRESULT.S_OK)
+			return new IEnumFromCom<Guid>(penum.Next, penum.Reset).Select(g => GetCat(g)).GetEnumerator();
+		return Enumerable.Empty<ShellFolderCategory>().GetEnumerator();
 	}
 
 	/// <inheritdoc/>