Is there some event showing that new ContentTemplate is completely applied?

Question

I have a ContentControl that I want to change it's ContentTemplate in some event. I want to add some values (text to TextBox) when control in ContentTemplate loaded. But, I has discovered that new ContentTemplate is applied (in terms of loading all controls of new template) NOT DIRECTLY after changing property ContentTemplate.

myContentControl.ContentTemplate = newContentTemplate;
// at this line controls of new template are not loaded!

I tested by added this code after that line:

var cp = GetVisualChild<ContentPresenter>(myContentControl);
var txt = myContentControl.ContentTemplate.FindName("Path_Cover", cp) as TextBox;
txt.Text = "test";

GetVisualChild

private T GetVisualChild<T>(DependencyObject parent) where T : Visual
    {
        T child = default(T);
        int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
        for (int i = 0; i < numVisuals; i++)
        {
            Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
            child = v as T;
            if (child == null)
            {
                child = GetVisualChild<T>(v);
            }
            if (child != null)
            {
                break;
            }
        }
        return child;
    }

I've got an error:

This operation is valid only on elements that have this template applied.

Is there some event showing that new ContentTemplate is completely applied?

EDIT 1

@eran I tried onApplyTemplate

public override void OnApplyTemplate()
{
   var cp = GetVisualChild<ContentPresenter>(Content_Option);
   var txt = Content_Option.ContentTemplate.FindName("Path_Cover", cp) as TextBox;
   txt.Text = "test";
}

but got error:

Object reference not set to an instance of an object.

EDIT 2

this "dirty" method works just fine:

myContentControl.ContentTemplate = newContentTemplate;

System.Windows.Threading.DispatcherTimer timer = new System.Windows.Threading.DispatcherTimer();
timer.Interval = TimeSpan.FromMilliseconds(0.000001);
timer.Tick += new EventHandler(delegate(object s, EventArgs a)
{
   timer.Stop();
   var cp = GetVisualChild<ContentPresenter>(Content_Option);
   var txt = Content_Option.ContentTemplate.FindName("Path_Cover", cp) as TextBox;
   txt.Text = "teSt";
});
timer.Start();

can somebody help me to achieve the same result with more "clean" (profesional) way :)

EDIT 3

My Scenario is, I have a TreeView (on left side) as menu and a Grid (on right side) as display for ContentControl. TreeView has some nodes. Each node has it's own DataTemplate. Each time a TreeView node clicked, a DataTemplate is set to ContentControl and a value (ex. Path_Cover.Text) is set from database. The layout more or less like windows explorer.

Well, this is all necessary code:

XAML

    <UserControl.Resources>

      <DataTemplate x:Key="General">
        <StackPanel>
           <DockPanel>
               <TextBlock Text="Cover"/>
               <TextBox Name="Path_Cover"/>
           </DockPanel>
           <DockPanel>
               <TextBlock Text="Slide"/>
               <TextBox Name="Path_Slide"/>
           </DockPanel>
        </StackPanel>
      </DataTemplate>

      <DataTemplate x:Key="Appearance">
        <StackPanel>
           <DockPanel>
               <TextBlock Text="Cover"/>
               <TextBox Name="Path_Cover"/>
           </DockPanel>
           <DockPanel>
               <Button Content="Get Theme"/>
               <TextBox Name="Txt_Theme"/>
           </DockPanel>
        </StackPanel>
      </DataTemplate>

    <UserControl.REsources>

<Grid>
    <ContentControl Name="myContentControl"/>
</Grid>

Code Behind

private void TreeMenu_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
   myContentControl.ContentTemplate =(DataTemplate)this.Resources[Tree_Menu.SelectedItem.ToString()];

   System.Windows.Threading.DispatcherTimer timer = new System.Windows.Threading.DispatcherTimer();
   timer.Interval = TimeSpan.FromMilliseconds(0.000001);
   timer.Tick += new EventHandler(delegate(object s, EventArgs a)
   {
      timer.Stop();
      switch (Tree_Menu.SelectedItem.ToString())
      {
         case "General": 
               var cp = GetVisualChild<ContentPresenter>(Content_Option);
               var txt = Content_Option.ContentTemplate.FindName("Path_Cover", cp) as TextBox;
               txt.Text = "test";

               txt = Content_Option.ContentTemplate.FindName("Path_Slide", cp) as TextBox;
               txt.Text = "test";
               break;

        case "Appearance": 
               var cp = GetVisualChild<ContentPresenter>(Content_Option);
               var txt = Content_Option.ContentTemplate.FindName("Txt_Theme", cp) as TextBox;
               txt.Text = "test";
               break;
      }
   });
   timer.Start();
}

I'm just need to "move" the code inside timer.tick event handler to some new event that fire after DataTemplate/ContentTemplate completely applied.

Answer 1

I'm aware this is quite an old question but I've been looking for an answer to this and having invented one, thought this would be a good place to share it.

I have simply created my own ContentPresenter class extending from the standard ContentPresenter:

public class ContentPresenter : System.Windows.Controls.ContentPresenter {

    #region RE: ContentChanged
    public static RoutedEvent ContentChangedEvent = EventManager.RegisterRoutedEvent("ContentChanged", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(ContentPresenter));
    public event RoutedEventHandler ContentChanged {
        add { AddHandler(ContentChangedEvent, value); }
        remove { RemoveHandler(ContentChangedEvent, value); }
    }
    public static void AddContentChangedHandler(UIElement el, RoutedEventHandler handler) {
        el.AddHandler(ContentChangedEvent, handler);
    }
    public static void RemoveContentChangedHandler(UIElement el, RoutedEventHandler handler) {
        el.RemoveHandler(ContentChangedEvent, handler);
    }
    #endregion

    protected override void OnVisualChildrenChanged(System.Windows.DependencyObject visualAdded, System.Windows.DependencyObject visualRemoved) {
        base.OnVisualChildrenChanged(visualAdded, visualRemoved);
        RaiseEvent(new RoutedEventArgs(ContentChangedEvent, this));
    }
}

I hope this may help those of you out there looking for a simple solution to this glaring oversight in the design of ContentPresenter.