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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: gtkada evenhandler on_procedure method , how to access children
 of topwindow in the eventhandler
Date: Sat, 2 Nov 2019 12:03:20 +0100
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Xref: reader01.eternal-september.org comp.lang.ada:57442
Date: 2019-11-02T12:03:20+01:00
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On 2019-11-02 11:22, Alain De Vos wrote:
> 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;

It is possible to enumerate children of a container, but that is not the 
recommended way as it is weakly typed and fragile. A better way is a 
derived widget. It is very easy to drive customized widgets in GtkAda. E.g.

    type My_Box_Record is new Gtk_VBox with -- Derive from VBox
        Button : Gtk_Button;
        Label  : Gtk_Label;
    end record;
    type My_Box is access all My_Box_Record;
    procedure Gtk_New (Box : out My_Box);

Creation:

    procedure Gtk_New (Box : out My_Box) is
    begin
       Box := new My_Box_Record;
       Initialize_Vbox (Box); -- Parent's initialization from Gtk_Box
       Gtk_New (Box.Button);
       Box.Add (Box.Button);
       Gtk_New (Box.Label);
       Box.Add (Box.Label);

       -- Connect signal handlers here, pass My_Box to them

    end Get_New;

Put declaration of the custom widget in a separate package. All handlers 
go into the package body. [This will reduce the inevitable mess GTK 
imposes on any otherwise cleanly designed Ada application]

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de