You can obtain this service from the design-time environment object hosting your designer, which will implement System.IServiceProvider (that's the Site for a Component). It can be used to obtain various functions that you may require to present your designer's UI.

CanShowComponentEditor() determines whether the environment supports the display of a ComponentEditorForm for the specified component. You can then use ShowComponentEditor() to show the editor. ShowDialog() will display the specified Form modally, returning a System.Windows.Forms.DialogResult. ShowMessage( ) and ShowError() display a message in a message box, with the appropriate warning icon, and ShowToolWindow() displays the tool window with the specified Guid. (Some standard GUIDs can be found in the System.ComponentModel.Design.StandardToolWindows class).

You can also mark the UI as dirty (and therefore needing an update), with SetUIDirty(), and retrieve a System.Windows.Forms.IWin32Window to use as the owner for your dialogs with the GetDialogOwnerWindow() method.

public interface IUIService {
// Public Instance Properties
   public IDictionary Styles{get; }
// Public Instance Methods
   public bool CanShowComponentEditor(object component);
   public IWin32Window GetDialogOwnerWindow();
   public void SetUIDirty();
   public bool ShowComponentEditor(object component, System.Windows.Forms.IWin32Window parent);
   public DialogResult ShowDialog(System.Windows.Forms.Form form);
   public void ShowError(Exception ex);
   public void ShowError(Exception ex, string message);
   public void ShowError(string message);
   public DialogResult ShowMessage(string message, string caption, System.Windows.Forms.MessageBoxButtons buttons);
   public void ShowMessage(string message);
   public void ShowMessage(string message, string caption);
   public bool ShowToolWindow(Guid toolWindow);
}