4. MasterPage

The MasterPage does the following:

1. Includes the component

   <%@ Register Src="~/Controls/MessageBox.ascx" TagName="ucMessageBox" TagPrefix="ctrls" %>
   <asp:UpdatePanel ID="upMessages" runat="server" UpdateMode="Conditional">
       <contenttemplate>
           <ctrls:ucMessageBox ID="ctlMessageBox" runat="server" Visible="false" OnResponse="ctlMessageBox_OnResponse" />
       </contenttemplate>
   </asp:UpdatePanel>

2. Declares the same events to forward them

   /// <summary>
   /// The message box OnResponse CommandEventHandler
   /// </summary>
   public delegate MessageBoxEventHandler OnResponseMessageBox(object sender, MessageBoxEventArgs e);

   /// <summary>
   /// The message box response event
   /// </summary>
   public event MessageBoxEventHandler ResponseMessageBox;

3. Handles the component events and forward them to pages (System.Web.UI.Page), see 5 in this wiki

   /// <summary>
   /// Handles the OnResponse event of the ctlMessageBox control.
   /// </summary>
   /// <param name="sender">The source of the event.</param>
   /// <param name="e">The <see cref="MessageBoxEventArgs"/> instance containing the event data.</param>
   protected void ctlMessageBox_OnResponse(object sender, MessageBoxEventArgs e)
   {
       if (null != this.ResponseMessageBox)
       {
           this.ResponseMessageBox(
               sender,
               e);
       }
       else
       {
           // Loosing the user response
       }
   }