How to access a object on a page from a function (in the page class)..?

Hi all

I have - hope so - a trivial problem for the crack's...
I want to access an object on a page (e.g. label, stacklayout, etc.) from a function (in page-class) e.g. to make it visible / invisible or to update text to a label.

If I access an object from an event-handler in the page-class (e.g. item.tapped) it works.
If I want to access the object from an own function, the object is “not known in this context”.
I have tried this. page. pagename. - nothing works...

What do I have to do, to access an object on the page from a function…?

Thanks for any suggestion...

Concrete example (note: do't care about the messagingcenter and the stacklayout - I also have the problem with a simple label):

Definition of object:

var DatenLadenIndicator = new ActivityIndicator
  {
    HorizontalOptions = LayoutOptions.CenterAndExpand,
    Color = Color.Black,
    IsRunning = true,
    IsVisible = true,
  };
var DatenLadenLabel = new Label { Text = "Daten werden geladen...", Font = Font.SystemFontOfSize(20, FontAttributes.Bold) };
var DatenLadenElement = new StackLayout { Children = { DatenLadenLabel, DatenLadenIndicator } };
DatenLadenElement.IsVisible = false;

The DatenLadenElement then is added to the page-content:

Content = new StackLayout // Inhalt Page aufbereiten
{
  Padding = 10,
  Children = 
   { 
    DatenLadenElement, 
    LSortierung, 
    LVSortierung,
    lStatusAbfrage, 
    lvErgebnisAnzeige,
   }

Function to show/hide the DatenLadenElement:

public void DatenLadenAnzeigen()
{
  DatenLadenElement.IsVisible = true;
  MessagingCenter.Subscribe<GV.UpdateStatusMessageData>(this, GV.UpdateStatusMessageData.MessageIDAbfrageBeendet, async (msg) =>
  {
    DatenLadenElement.IsVisible = false;
    MessagingCenter.Unsubscribe<GV.UpdateStatusMessageData>(this, GV.UpdateStatusMessageData.MessageIDAbfrageBeendet);
  });
return;
}