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From: Gavin McCord <gavind.mccord@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: On_Button_Press_Event in Text_View
Date: Wed, 14 Aug 2024 14:34:13 -0000 (UTC)
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On Wed, 14 Aug 2024 14:03:24 +0200, Dmitry A. Kazakov wrote:

> On 2024-08-14 13:42, Gavin McCord wrote:
>> On Tue, 13 Aug 2024 22:29:59 +0200, Dmitry A. Kazakov wrote:
>> 
>>> On 2024-08-13 13:37, Gavin McCord wrote:
>>>
>>>> I have a custom handler used when I update the Text_Buffer:
>>>>
>>>>    Button_Callback.Connect
>>>>      (Update_Button, "clicked", Update_Clicked'Access,
>>>>       Buffer_To_Pass);
>>>>
>>>> That works fine so I was imagining something similar might be
>>>> possible,
>>>> but I've run through various permuations of records and access types
>>>> but not yet got a working callback.
>>>>
>>>> Any help gratefully received (I can post the full code if that's
>>>> useful).
>>>
>>> Something like this:
>>>
>>>      package Event_Handlers is
>>>         new Gtk.Handlers.User_Return_Callback
>>>             (  GObject_Record,
>>>                Boolean, User_Data_Type
>>>             );
>>>
>>>
>>>      function On_Button_Press
>>>               (  Object : access GObject_Record'Class;
>>>                  Event  : Gdk_Event; Data   : User_Data_Type
>>>               )  return Boolean;
>>>
>>>
>>>      View.Set_Events (View.Get_Events or Button_Press_Mask);
>>>      Event_Handlers.Connect (  View,
>>>         "button-press-event",
>>>         Event_Handlers.To_Marshaller (On_Button_Press'Access),
>>>         Data
>>>      );
>> 
>> Thank you. That allows me to pass a record of the buffer.
> 
> As a general advice. Usually you have a custom widget derived from
> Gtk_Grid_Record servicing as the main window.
> 
>     type Main_Window_Record is new Gtk_Grid_Record with record
>        Button    : Gtk_Button;
>        Text_View : Gtk_Text_View;
>        Buffer    : Gtk_Text_Buffer;
>        ...
>     type Main_Window is access all Main_Window_Record'Class;
> 
> Main_Window you pass to all handlers, so that you always have a full
> context in any of them.
> 
>> There's only one other thing.
>> 
>> If I try to check the Event I get another error, such as
>> 
>>   function On_Button_Press [skipped lines]
>> 
>>      if Event.The_Type = Gdk_2button_Press then
>>         Put_Line ("double-click");
>>      end if;
>> 
>> Attempting to compile that gives me
>> 
>>     error: cannot reference discriminant of unchecked union
> 
>     case Get_Event_Type (Event) is
>        when Button_Press =>
>           ...
>        when Gdk_2Button_Press | Gdk_3Button_Press =>
>           ...
>        when Key_Press =>
>           case Get_Key_Val (Event) is
>              when GDK_Up | GDK_KP_Up =>
>                 ...
>              when GDK_Down | GDK_KP_Down =>
>                 ...
>           end case;
>           ...
>        when others =>
>           ...
>     end case;

I've got it working now. Get_Event_Type (Event) is what I needed.

Thank you again for all your help.

Gavin