Gewusst wie: Implementieren eines Designers für ein Steuerelement

		//
		// <doc>
		// <desc>
		//      This is a designer for the HelpLabel.  This designer provides
		//      design time feedback for the label.  The help label responds
		//      to changes in the active control, but these events do not
		//      occur at design time.  In order to provide some usable feedback
		//      that the control is working the right way, this designer listens
		//      to selection change events and uses those events to trigger active
		//      control changes.
		// </desc>
		// </doc>
		//
        [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")] 
		public class HelpLabelDesigner : System.Windows.Forms.Design.ControlDesigner 
		{

			private bool trackSelection = true;

			/// <summary>
			/// This property is added to the control's set of properties in the method
			/// PreFilterProperties below.  Note that on designers, properties that are
			/// explictly declared by TypeDescriptor.CreateProperty can be declared as
			/// private on the designer.  This helps to keep the designer's publi
			/// object model clean.
			/// </summary>
            [DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )]
			private bool TrackSelection
			{
				get
				{
					return trackSelection;
				}
				set
				{
					trackSelection = value;
					if (trackSelection)
					{
						ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
						if (ss != null)
						{
							UpdateHelpLabelSelection(ss);
						}
					}
					else
					{
						HelpLabel helpLabel = (HelpLabel)Control;
						if (helpLabel.activeControl != null)
						{
							helpLabel.activeControl = null;
							helpLabel.Invalidate();
						}
					}
				}
			}

			public override DesignerVerbCollection Verbs
			{
				get
				{
					DesignerVerb[] verbs = new DesignerVerb[] {
																  new DesignerVerb("Sample Verb", new EventHandler(OnSampleVerb))
															  };
					return new DesignerVerbCollection(verbs);
				}
			}

			//
			// <doc>
			// <desc>
			//      Overrides Dispose.  Here we remove our handler for the selection changed
			//      event.  With designers, it is critical that they clean up any events they
			//      have attached.  Otherwise, during the course of an editing session many
			//      designers may get created and never destroyed.
			// </desc>
			// </doc>
			//
			protected override void Dispose(bool disposing) 
			{
				if (disposing) 
				{
					ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
					if (ss != null) 
					{
						ss.SelectionChanged -= new EventHandler(OnSelectionChanged);
					}
				}

				base.Dispose(disposing);
			}

			//
			// <doc>
			// <desc>
			//       Overrides initialize.  Here we add an event handler to the selection service.
			//      Notice that we are very careful not to assume that the selection service is
			//      available.  It is entirely optional that a service is available and you should
			//      always degrade gracefully if a service could not be found.
			// </desc>
			// </doc>
			//
			public override void Initialize(IComponent component) 
			{
				base.Initialize(component);

				ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
				if (ss != null) 
				{
					ss.SelectionChanged += new EventHandler(OnSelectionChanged);
				}
			}

			private void OnSampleVerb(object sender, EventArgs e)
			{
				MessageBox.Show("You have just invoked a sample verb.  Normally, this would do something interesting.");
			}

			//
			// <doc>
			// <desc>
			//      Our handler for the selection change event.  Here we update the active control within
			//      the help label.
			// </desc>
			// </doc>
			//
			private void OnSelectionChanged(object sender, EventArgs e) 
			{
				if (trackSelection)
				{
					ISelectionService ss = (ISelectionService)sender;
					UpdateHelpLabelSelection(ss);
				}
			}

			protected override void PreFilterProperties(IDictionary properties)
			{
				// Always call base first in PreFilter* methods, and last in PostFilter*
				// methods.
				base.PreFilterProperties(properties);

				// We add a design-time property called "TrackSelection" that is used to track
				// the active selection.  If the user sets this to true (the default), then
				// we will listen to selection change events and update the control's active
				// control to point to the current primary selection.
				properties["TrackSelection"] = TypeDescriptor.CreateProperty(
					this.GetType(),        // the type this property is defined on
					"TrackSelection",    // the name of the property
					typeof(bool),        // the type of the property
					new Attribute[] {CategoryAttribute.Design});    // attributes
			}

			/// <summary>
			/// This is a helper method that, given a selection service, will update the active control
			/// of our help label with the currently active selection.
			/// </summary>
			/// <param name="ss"></param>
			private void UpdateHelpLabelSelection(ISelectionService ss)
			{
				Control c = ss.PrimarySelection as Control;
				HelpLabel helpLabel = (HelpLabel)Control;
				if (c != null)
				{
					helpLabel.activeControl = c;
					helpLabel.Invalidate();
				}
				else
				{
					if (helpLabel.activeControl != null)
					{
						helpLabel.activeControl = null;
						helpLabel.Invalidate();
					}
				}
			}
		}