Re: GtkAda callback and event

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2021-09-04 23:39, DrPi wrote:

> I use an event callback with user data.
> 
> I first declare a package :
>     package Handler_Motion_Notify is new 
> Gtk.Handlers.User_Return_Callback (Widget_Type => 
> Gtk.Text_View.Gtk_Text_View_Record,
> 
>     Return_Type => Boolean,
> 
>     User_Type   => t_Debug_Panel);
> 
> The function callback is declared like this :
>     function On_Motion_Notify (TextView : access 
> Gtk.Text_View.Gtk_Text_View_Record'Class;
>                                DebugPanel : t_Debug_Panel) return Boolean;

This is wrong. The motion-notify-event callback has the parameters:

1. Target
2. Gdk.Event.Gdk_Event_Motion
3. User data

> The connection is done like this :
>        Handler_Motion_Notify.Connect (Widget => Panel.TextView,
>                                       Name   => 
> Gtk.Widget.Signal_Motion_Notify_Event,
>                                       Cb     => On_Motion_Notify'Access,
>                                       User_Data => t_Debug_Panel(Panel));
> 
> This works correctly. But... I need to have access to the event in the 
> callback function.

Maybe it does not crash but it is incorrect.

> How can I achieve this ?

There is no shortcut Connect and Callback defined in 
User_Return_Callback. Therefore you have to use a general-case callback 
with the parameter list:

    function On_Motion_Notify
             (  Object : access Gtk_Text_View_Record'Class;
                Params : Glib.Values.GValues;
                Data   : t_Debug_Panel
             )  return Boolean;

connected as:

    Handler_Motion_Notify.Connect
    (  Panel.TextView,
       "motion-notify-event", -- = Signal_Motion_Notify_Event
       On_Motion_Notify'Access,
       t_Debug_Panel (Panel)
    );

The parameter is accessed using the function Nth or 
Gtk.Argument.Unchecked_To_Gdk_Event_Motion, e.g.

    Gtk.Argument.Unchecked_To_Gdk_Event_Motion (Params, 1)

P.S. Since the target is practically never used in callbacks, you can 
instantiate Gtk.Handlers.User_Return_Callback with GObject_Record. This 
way you could use it with all types of widgets. That reduces the number 
of instantiations.

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