'Inheriting' from an Internal WinForms Designer

using System;
using System.Collections;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Diagnostics;
using System.Reflection;
using System.Windows.Forms;

namespace EncapsulatedDesigner
{
    /// <summary>
    /// Designer for controls, deriving from <see cref="ToolStripDropDown"/>.
    /// Overriden members are delegated to an encapsulated default System.Windows.Forms.Design.ToolStripDropDownDesigner.
    /// </summary>
    /// <remarks>System.Windows.Forms.Design.ToolStripDropDownDesigner is marked internal.</remarks>
    internal abstract class ToolStripDropDownDesigner : ComponentDesigner
    {
        #region Fields

        protected ComponentDesigner defaultDesigner;
        protected IDesignerFilter designerFilter;

        #endregion

        #region Initialize & Dispose

        public override void Initialize(IComponent component)
        {
            // internal class ToolStripDropDownDesigner : ComponentDesigner
            // Name: System.Windows.Forms.Design.ToolStripDropDownDesigner , Assembly: System.Design, Version=4.0.0.0 
            Type tDesigner = Type.GetType("System.Windows.Forms.Design.ToolStripDropDownDesigner, System.Design");
            defaultDesigner = (ComponentDesigner)Activator.CreateInstance(tDesigner, BindingFlags.Instance | BindingFlags.Public, null, null, null);
            designerFilter = defaultDesigner;

            // use Designer properties of nested designer ( do before base.Initialize ! )
            TypeDescriptor.CreateAssociation(component, defaultDesigner);

            IServiceContainer site = (IServiceContainer)component.Site;
            if (site != null && GetService(typeof(DesignerCommandSet)) == null)
            {
                site.AddService(typeof(DesignerCommandSet), new CDDesignerCommandSet(this));
            }
            else { Debug.Fail("site != null && GetService(typeof (DesignerCommandSet)) == null"); }

            defaultDesigner.Initialize(component);
            base.Initialize(component);
        }

        public override void InitializeNewComponent(IDictionary defaultValues)
        {
            base.InitializeNewComponent(defaultValues);
            defaultDesigner.InitializeNewComponent(defaultValues);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (defaultDesigner != null)
                {
                    defaultDesigner.Dispose();
                }
            }

            base.Dispose(disposing);
        }

        #endregion

        #region IDesignerFilter overrides

        // ToolStripDropDownDesigner only overrides ComponentDesigner.PreFilterProperties()
        // base(ComponentDesigner).PreFilterAttributes() is empty
        // base(ComponentDesigner).PreFilterEvents() is empty
        // base(ComponentDesigner).PostFilterProperties() only if (this.Component is IPersistComponentSettings)

        protected override void PreFilterProperties(IDictionary properties)
        {
            designerFilter.PreFilterProperties(properties);
        }

        protected override void PostFilterAttributes(IDictionary attributes)
        {
            designerFilter.PostFilterAttributes(attributes);

            // will set this.InheritanceAttribute property from nested designer attributes, if control is inherited
            base.PostFilterAttributes(attributes);
#if DEBUG
            if (attributes.Contains(typeof(InheritanceAttribute)))
            {
                Debug.Assert(base.InheritanceAttribute == attributes[typeof(InheritanceAttribute)]);
            }
            else
            {
                Debug.Assert(base.InheritanceAttribute == InheritanceAttribute.NotInherited);
            }
#endif
        }

        protected override void PostFilterEvents(IDictionary events)
        {
            // filters events based on InheritanceAttribute
            designerFilter.PostFilterEvents(events);
        }

        #endregion

        #region Overrides

        public override ICollection AssociatedComponents
        {
            get { return defaultDesigner.AssociatedComponents; }
        }

        // only defaultDesigner.ActionLists is invoked, unless CDDesignerCommandSet is used
        // DesignerActionService queries via DesignerCommandSet for ActionLists and Verbs
        public override DesignerActionListCollection ActionLists
        {
            get { return defaultDesigner.ActionLists; }
        }

        #endregion

        #region DesignerCommandSet

        private class CDDesignerCommandSet : DesignerCommandSet
        {
            private readonly ComponentDesigner componentDesigner;

            public CDDesignerCommandSet(ComponentDesigner componentDesigner)
            {
                this.componentDesigner = componentDesigner;
            }

            public override ICollection GetCommands(string name)
            {
                if (name.Equals("Verbs"))
                {
                    // componentDesigner.Verbs & defaultDesigner.Verbs are empty
                    return null;
                }
                if (name.Equals("ActionLists"))
                {
                    return componentDesigner.ActionLists;
                }
                return base.GetCommands(name);
            }
        }

        #endregion
    }
}