I'm developing an autosizingtoolbar control that is a composite of a few other controls, including a FlowLayoutPanel. The contents of the internal FlowLayoutPanel determine the height of the toolbar. I've written a designer forthe control that reparents any controls dropped onto it to the internal FlowLayoutPanel.I then need to resize the FlowLayoutPanel and the control which contains it, so I thentrigger a method in the composite control's class that handles the control's internal layout at runtime (which works fine!).
At design time, unfortunately, in that layout method when I request the FlowLayoutPanel's preferred size for a given width, it ignores the most recently added control and returns the size one control too small. I've tried everything I could think of to force a layout in the FlowLayoutPanel before asking for its preferred size, but it never does any good. I've also verified that the most recently added control is indeed in the FlowLayoutPanel's controls collection. I think I just need to tell the designer host something, but I'm not sure how. Using the ComponentChangeService.OnComponentChanged method with the FlowLayoutPanel as the component argument didn't seem to help. I appreciate any suggestions.

Thank you,
Josh Usovsky

protected override void OnDragDrop(DragEventArgs de)
		{
			DesignerTransaction transaction = null;
			IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));
			IComponentChangeService changeService = (IComponentChangeService)GetService(typeof(IComponentChangeService));

			IToolboxService toolboxService = (IToolboxService)GetService(typeof(IToolboxService));
			ToolboxItem toolboxItem = toolboxService.GetSelectedToolboxItem();
			if (toolboxItem != null)
			{
				//Dropping a toolbox item
				//TODO: Finish this section after proof of concept
				transaction = host.CreateTransaction("MovingDroppedToolboxControl");
				IComponent[] comps = toolboxItem.CreateComponents();
				changeService.OnComponentChanging(this.control.Toolbar, null);
				this.control.Toolbar.Controls.Add(comps[0] as Control);
				changeService.OnComponentChanged(this.control.Toolbar, null, null, null);
				transaction.Commit();
			}
			else if (!(this.Control as FlowToolbar).flowLayoutPanel.Contains(this.controlBeingDragged))
			{
				if (host != null && changeService != null)
				{
					transaction = host.CreateTransaction("MovingControl");
					changeService.OnComponentChanging(control.Toolbar, null);
					control.Toolbar.Controls.Add(this.controlBeingDragged);
					changeService.OnComponentChanged(this.control.Toolbar, null, null, null);
					transaction.Commit();
					(this.Control as FlowToolbar).flowLayoutPanel.PerformLayout();
					(this.Control as FlowToolbar).LayoutChildren();
				}

			}
		}

PropertyDescriptor descriptor = TypeDescriptor.GetProperties(this.controlBeingDragged)["Parent"];
			if (descriptor != null)
			{
				descriptor.SetValue(this.controlBeingDragged, this.Control as FlowToolbar).flowLayoutPanel);

			}