gtkada evenhandler on_procedure method , how to access children of topwindow in the eventhandler

[Alain De Vos <devosalain71@gmail.com>]

I have a window with obe button and one label and want to change the text on the label when the button is pressed in the eventhandler, I pass the top window.

procedure hello is
   Top     : Gtk.Window.Gtk_Window;
   Button  : Gtk_Button;
   Label   : Gtk_Label;
   VBox    : Gtk_Box;
   procedure Create_Window is
   begin
      Gtk.Window.Gtk_New
        (Window   => Top,
         The_Type => Gtk.Enums.Window_Toplevel);
      Gtk.Window.Set_Title (Window => Top, Title  => "Hello from ADA");
      Gtk_New(Button);
      Button.On_Clicked (Call => On_Button_Click'Access, 
                         Slot => Top);
      Gtk_New(Label);
      Gtk_New_Vbox(VBox);
      Add (VBox,Button);
      Add (VBox,Label);
      Add (Top,VBox);
      Gtk.Window.Show_All (Top);
   end Create_Window;
begin
   Gtk.Main.Init;
   Create_Window;
   Gtk.Main.Main;
end hello;

I pass the topwindow to the eventhandler(slot).
In the eventhandler I need go from the Top to the Vbox to the Label and set the text on the label ... button pressed. I probably need to set a property in the main and query it in the handler and cast the correct type ...
{The label is not directly visible in the handler ...}

package body buttonhandler is
   procedure On_Button_Click (Top : access Glib.Object.GObject_Record'Class) is
   begin
      Put_line ("Hallo");
      -- I need to go from Top to Vbox to Label and set text ... ????
   end On_Button_Click;
end buttonhandler;