I want to change from a instance of a class the height of a child.
The problem is, that the canvas did not “saves” it height when running the function Compute_Change_height_of_ressource.

I have this class

 public partial class RessourceTreeViewItem : TreeViewItem  {
  public int RG_ID { get; set; }

  public double height_of_ressource { get; set; }

  StackPanel taskPanel { get; set; }


  Label taskLabel { get; set; }

  public String RGLabeltxt { get; set; }

  public Canvas backgroundcanvas { get; set; }

  public ScrollViewer scrollViewer { get; set; }

  public DateTime startdatetime { get; set; }

  public DockPanel panel { get; set; }

  public RessourceTreeViewItem(int RG_ID, double dots_per_minute, DateTime startdatetime, DateTime enddatetime, String RGLabeltxt, double height_of_ressource)
    {
        this.RGLabeltxt = RGLabeltxt;
        this.RG_ID = RG_ID;
        this.startdatetime = startdatetime;
        this.height_of_ressource = height_of_ressource;

        this.panel = new DockPanel();
        this.panel.HorizontalAlignment = HorizontalAlignment.Left;
        

        this.taskLabel = new Label() { 
            Content = this.RGLabeltxt 
        };

        this.taskLabel.Width = 40;

        this.Margin = new Thickness(-40, 0, 0, 0);

        this.backgroundcanvas = new Canvas();

        this.backgroundcanvas.Height = this.height_of_ressource;

        this.scrollViewer = new ScrollViewer();
        this.scrollViewer.HorizontalScrollBarVisibility = ScrollBarVisibility.Hidden;
        this.scrollViewer.VerticalScrollBarVisibility = ScrollBarVisibility.Disabled;

        this.scrollViewer.Content = this.backgroundcanvas;

        // Add the task label and the scroll viewer to the task panel
        this.panel.Children.Add(taskLabel);
        this.panel.Children.Add(this.scrollViewer);
        this.Header = this.panel;

      

    }

    public void Compute_Change_height_of_ressource(double height_of_ressource)
    {

        foreach (TimeLineItem item in this.backgroundcanvas.Children)
        {
            item.Compute_Change_height_of_ressource(height_of_ressource);
        }
        this.height_of_ressource = height_of_ressource;
        this.panel.Height = height_of_ressource;
        this.scrollViewer.Height = height_of_ressource;
        this.backgroundcanvas.Height = height_of_ressource;
        

    }

My Problem is, as when I want to update via Compute_Change_height_of_ressource, the backgroundcanvas.Height does not change its height as I see in debug.
All other attributes were changed.
In the visual tree, there is ScrollContentPresenter the parent of the backgroundcanvas, which has the old height – how can i change it?