The run order about Loaded event and OnApplyTemplate in custom control of Silverlight 2 beta 2

I' ve created a customer control MenuLink.cs in silverlight 2beta2, and the code like this:

1. public class MenuLink : Control
2.  { 
3.         public MenuLink( )
4.         {          
5.             DefaultStyleKey = typeof(MenuLink);
6.             this.Loaded += new RoutedEventHandler(MenuLink_Loaded);
7.         }
9.         void MenuLink_Loaded(object sender, RoutedEventArgs e)
10.         {
11.             
12.         }
13.        
14.         public override void OnApplyTemplate()
15.         {
16.             base.OnApplyTemplate();           
17.         }
18. }

There is a canvas named 'canMenu' in page 'Page.xaml', and i add the menulink into the canvas dynamicly:

1.  public Page()
2.         {
3.             InitializeComponent();
4.             this.Loaded += new RoutedEventHandler(Page_Loaded);            
5.         } 
7.         void Page_Loaded(object sender, RoutedEventArgs e)
8.         {
9.             MenuLink ml = new MenuLink(true);            
10.             canMenu.Children.Clear();
11.             canMenu.Children.Add(ml);
12.         }

In this situation, the event in MenuLink.cs are called by this orders:

1. 1. public MenuLink( bool a )
2. 2. void MenuLink_Loaded(object sender, RoutedEventArgs e)
3. 3. public override void OnApplyTemplate()

But if i add the menulink after downloading a xml file in page.cs like this:

1.   public Page()
2.         {
3.             InitializeComponent();
4.             this.Loaded += new RoutedEventHandler(Page_Loaded);            
5.         } 
7.         void Page_Loaded(object sender, RoutedEventArgs e)
8.         {
9.             WebClient webclient = new WebClient();
10.             webclient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webclient_DownloadStringCompleted);
11.             webclient.DownloadStringAsync(new Uri("a.xml",UriKind.Relative));          
12.         }
14.         void webclient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
15.         {
16.             MenuLink ml = new MenuLink(true);            
17.             canMenu.Children.Clear();
18.             canMenu.Children.Add(ml);
19.         }

Then the order of events/methods called in MenuLink.cs like this:

1. 1. public MenuLink( bool a )
2. 2. public override void OnApplyTemplate()
3. 3. void MenuLink_Loaded(object sender, RoutedEventArgs e)

 

I really don't know why?????