Re: C++ call constructor via GtkItemFactoryEntry

[Jeff Franks <jcf tpg com au>]

William L. Thomson Jr. wrote:

> Jumping in with both feet.
>
> I have an app that each inner window is launched by the main app/window.
> Each window has it's own class.
>
> So far things are working the way I want them to for the most part.
> However I need to deviate from how I am currently doing things.
> Currently I call a function/method within the class directly from the
> main GTK menu.
>
> Ex:
> GtkItemFactoryEntry menu_items[] = {
>         {"/Manage/Invoices","<control>I",&ManageInvoices::displayWindow,0,null_gchar},
>         {"/_Help",null_gchar,NULL,0,"<LastBranch>"},
>         {"/Help/About",null_gchar,&About::displayWindow,0,null_gchar},
> };
>
> That works fine however I have a constructor to the class that does not
> get called. I need the constructor/destructor to be called so DSO's can
> be loaded/unloaded and my app work without a seg fault.
>
> I could just put the DSO loading code in the displayWindow function, but
> then I have to come up with a way to close out the DSO. Which currently
> is handled by the destructor. I also am having problems with calling the
> destructor.
>
> So my questions are as follows. 
>
> 1.) How can I call a C++ constructor from within my GTK menu without
> having to wrap it in another C or C++ function?
>
> I thought about doing an init() function like
> void ManageInvoices::init() {
>         ManageInvoices mi = new ManageInvoices();
>         mi.displayWindow;
> }
>
> Although I am not sure that's a good way to go, not to mention the
> additional codding. Is it OK to have an object create a new version of
> itself. Like in the above example?
>  
For menu_items above to work ManageInvoices::displayWindow has to be a 
static function, since C doesn't know about classes.  Static class 
functions don't have a 'this' and don't know about 
construcors/destructors either. For a C function/struct like menu_items, 
I think you will have to write a static creation function, like 'init' 
to create an instance of your window. This is common practice in 
application Frameworks..

> 2.) How can I call my C++ destructor during window closing?
You don't call destructors directly. If the window is a transient window 
just create it on the stack and the destructor will be called when it 
goes out of scope. If it is created by a call to 'new' you will have to 
call 'delete', which will call your destructor. You can then destroy any 
GTK+ C resources from inside the window's destructor. So in response to 
a user action to close the window, call something like 'delete window' 
and this call the window destructor.

> Of course I can place a button on my new window and have it call some
> function that will call the destructor and close the window. Although if
> someone closes the window via the window managers close/X button I need
> to detect that and call the destructor.
>
>  
GTK+  provides the mechanism to add a C function to a widget that will 
get called when a widget is destroyed. You can use this function to call 
'delete'. This works no matter how the window is closed, by calling 
gtk_object_destroy() or by the window manager. (I can post some code if 
you need it.)

> Neither my c'tors and d'tors take any arguments, and for some reason I
> am thinking that a c'tor or d'tor is being called for the object/class
> to exist when I see the window.
>
> However I know that my c'tors and d'tors are not being called.
>
> Further more I know I may not be doing things the best or proper way.
> Currently I am still learning C/C++ and GTK in the process. So please be
> kind in your responses if I am asking the obvious.
>
>  

Regards Jeff Franks.