Re: Exception Handling within Gtkada

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

On 2021-09-22 10:42, ldries46 wrote:
> Op 21-9-2021 om 9:01 schreef Dmitry A. Kazakov:
>> On 2021-09-21 08:49, Vadim Godunko wrote:
>>> On Monday, September 20, 2021 at 3:06:02 PM UTC+3, ldries46 wrote:
>>>> I want an exception to be seen within an existing window of Gtkada 
>>>> to be able to see details of the error. So I used:
>>>>
>>>> exception
>>>> when no_const =>
>>>> Main_Window.Buffer.Insert_At_Cursor
>>>> ("-------------------------------------------------------------------------" 
>>>>
>>>> & To_String(CRLF));
>>>> Main_Window.Buffer.Insert_At_Cursor("Error : io_const" & 
>>>> to_String(CRLF));
>>>> end Test_Exception;
>>>>
>>>> In this case the the program ends and the reason of the exception is 
>>>> lost. I want this only for a selected nr of exceptions. In this case 
>>>> the exception no_const.
>>>
>>> Generally, Ada exceptions must not left scope of callback function. 
>>> Thus, such code should be added to each callback/event handler/etc. 
>>> subprogram of your application.
>>
>> Right. Each handler should end like this:
>>
>>    exception
>>       when Error : others =>
>>          Glib.Message.Log
>>          (  "My fancy program",
>>             Log_Level_Critical,
>>             (  "Fault in On_Button_Click: "
>>             &  Exception_Information (Error)
>>          )  );
>>    end On_Button_Click;
>>
> I tried different approaches but they cannot solve my problem. Part of 
> the problem is probably that I am developing a package which should be 
> usable in all different kind of programs maybe even under programs using 
> all different kind of GUI's.

You still may not propagate exceptions through C.

> That means that exception handling cannot 
> always be done in the package but should be done in at least a package 
> calling that problem. With this approach I tried to solve an earlier 
> problem I asked about "Is there a way to see if a value is declared as a 
> constant". I tried to solve that problem in a way that needed Exception 
> handling during running to solve a design problem that could be made. I 
> will need another way to go around that problem.

Posing a problem correctly is a half of solution.

Anyway, if you want to propagate exceptions through GTK, that is 
possible to do by marshaling and then re-raising occurrence. GtkAda 
contributions does this in the package Gtk.Main.Router. It also gives 
stack trace of the exception in a popup dialog. And it can show the 
location in GPS if that is running in the server mode.

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