Collection Editor for Custom List type

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C#

Visual-Studio

Using VS Community 2015.

I have create a thread-safe list (TList<T>) that implements all of the standard list functionality in a thread-safe manner. I now have a user control that has a TList<ImageEntry> as a property. ImageEntry is an object derived from Component, with 3 properties. However, the CollectionEditor does not allow maintenance of this list in the designer.

The TList:

public class TList<T> : IList<T>, ICollection<T>, IEnumerable<T>, IDisposable {

private ReaderWriterLockSlim _lck = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
private List<T> _list = new List<T>();
private bool _lockableEnumerator = false;

public TList() { }
public TList(bool lockableEnumerator) : base() {
	_lockableEnumerator = lockableEnumerator;
}
public TList(IEnumerable<T> elements, bool lockableEnumerator = false) {
	_list.AddRange(elements);
	_lockableEnumerator = lockableEnumerator;
}
.... // All the list functionality here
}

The contents:

[DesignTimeVisible(false)]
public class ImageEntry : Component { 
	protected Bitmap _image = null;
	protected string _path = null;
	ImageDrawMode _sizemode = ImageDrawMode.Zoom;

	public ImageEntry() { }

	[DefaultValue(typeof(Bitmap), null)]
	public virtual Bitmap Image {
		get {
			if (_image == null) {
				if (!string.IsNullOrEmpty(_path))
					_image = new Bitmap(_path);
			}
			return _image;
		}
		set {
			_image = value;
			if (value != null)
				_path = null;
		}
	}
	[DefaultValue(typeof(string), "")]
	public virtual string Path {
		get { return _path ?? string.Empty; }
		set {
			if (string.IsNullOrEmpty(value))
				_path = null;
			else {
				_image = null;
				_path = value;
			}
		}
	}
	[DefaultValue(ImageDrawMode.Zoom)]
	public virtual ImageDrawMode SizeMode {
		get {
			return _sizemode;
		}
		set {
			_sizemode = value;
		}
	}
	public override string ToString() {
		return string.IsNullOrEmpty(_path) ? ((_image == null) ? null : _image.ToString()) : _path;
	}
}

The property:

TList<ImageEntry> _images = new TList<ImageEntry>();
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
[Description("The collection of images to cycle through")]
[Category("Effects")]
[Editor(typeof(CollectionEditor), typeof(UITypeEditor))]
public TList<ImageEntry> Images {
	get { return _images; }
}

When I bring up the CollectionEditor in the IDE, it does not show the ImageEntry properties on the right, and the Add and Remove buttons are disabled on the left. However, if I modify the Images property such that it returns the internal List<ImageEntry>, it all works fine (but then, of course, my Images property is not thread-safe).

I have tried putting together a custom Collection editor, but that didn't work either.

public class ImageEntryCollectionEditor : CollectionEditor {
	public ImageEntryCollectionEditor(Type type) : base(type) { }
	protected override Type[] CreateNewItemTypes() {
		return new Type[] { typeof(ImageEntry) };
	}
	protected override Type CreateCollectionItemType() {
		return typeof(ImageEntry);
	}
}

What am I missing here?