C#

private void RegisterControlEvent()
{
  Control control = this.NamingContainer.FindControl(ControlTrigger);
  if (control == null) { return; }

  string eventName = ControlCoverter.GetEventName(control);
  if (eventName == string.Empty) { return; }

  EventInfo ei = control.GetType().GetEvent(eventName);
  Delegate del = Delegate.CreateDelegate(ei.EventHandlerType, this, "Control_TriggerEvent");
  ei.AddEventHandler(control, del);
}

void Control_TriggerEvent(object sender, EventArgs e)
{
  Show();
}

protected void ImageMap2_Click(object sender, ImageMapEventArgs e)
{

}

public class ControlCoverter : ControlIDConverter
  {
    public override TypeConverter.StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
    {
      if (context == null) { return null; }

      IDesignerHost host1 = (IDesignerHost)context.GetService(typeof(IDesignerHost));
      if (host1 == null) { return null; }

      string[] textArray1 = this.GetControls(host1, context.Instance);
      if (textArray1 == null) { return null; }

      return new TypeConverter.StandardValuesCollection(textArray1);
    }

    // if a Control Supports the following events then it is allowed to trigger the MessageBox
    private static readonly string[] EventTriggers = new string[]
      {
        "Click", "SelectedIndexChanged", "CheckChanged", "ServerClick", "ServerChange",
      };

    private string[] GetControls(IDesignerHost host, object instance)
    {
      IContainer container1 = host.Container;
      IComponent component1 = instance as IComponent;
      if ((component1 != null) && (component1.Site != null)) { container1 = component1.Site.Container; }
      if (container1 == null) { return null; }

      ComponentCollection collection1 = container1.Components;
      ArrayList list1 = new ArrayList();

      foreach (IComponent component2 in collection1)
      {
        Control control1 = component2 as Control;

        // see if the control has an event that is in our 'known events' list
        EventInfo[] eventInfo = control1.GetType().GetEvents();
        bool supportsEvent = false;
        foreach (EventInfo ei in eventInfo)
        {
          string eventName = ei.Name;
          if (Array.IndexOf<string>(EventTriggers, eventName) != -1)
          {
            supportsEvent = true;
            break;
          }
        }

        if ((((control1 != null) && (control1 != instance)) && ((control1 != host.RootComponent) && (control1.ID != null))) &&
            ((control1.ID.Length > 0) && this.FilterControl(control1)) &&
             (supportsEvent))
        {
          list1.Add(control1.ID);
        }
      }
      list1.Sort(Comparer.Default);
      return (string[])list1.ToArray(typeof(string));
    }

    public static string GetEventName(Control control)
    {
      EventInfo[] eventInfo = control.GetType().GetEvents();
      foreach (EventInfo ei in eventInfo)
      {
        string eventName = ei.Name;
        if (Array.IndexOf<string>(EventTriggers, eventName) != -1)
        {
          return eventName;
        }
      }
      return string.Empty;
    }
  }