[gtkada] Canvas signal "item_select" - can't complile

[Stephen Leake]

Enno Bartels <enno.bartels at m.eads.net> writes:

> Here is my code:
> 
>    ----------------------------------------------------------------
>    --  Redefine our own item type, since we want to provide our own
>    --  graphics.
>    ----------------------------------------------------------------
>    type Display_Item_Record is new Canvas_Item_Record with record
>       Color : Gdk.Color.Gdk_Color;
>       W, H  : Gint;
>       Num   : Positive;
>       X, Y  : Gint;
>       Mode  : Integer;
>    end record;
>    type Display_Item is access all Display_Item_Record'Class;
> 
> ...................
> 
> package Canvas_Cb  is new Gtk.Handlers.Callback (Interactive_Canvas_Record);

Hmm. You declare "Display_Item_Record" above, but you are using
"Interactive_Canvas_Record" here. So I'm confused.

>  ----------------------------------------------------------------------------
>    -- procedure "Item_Select"
>  ----------------------------------------------------------------------------
>    procedure Item_Select
>      (Canvas : access Interactive_Canvas_Record'Class;
>       Item   : Canvas_Item)
>    is
>          It : Display_Item := Display_Item (Item);
>    begin
>      Text_Io.Put_Line ("item selected " & It.Num'Img);
>    end Item_Select;
> 
> ......................
> 
> Canvas        : Interactive_Canvas;
> ...
> Canvas_Cb.Object_Connect (Canvas, "item_selected",
>                    Canvas_Cb.To_Marshaller(Item_Select'Access), Canvas);

There is no version of "To_Marshaller" in Canvas_Cb that can take a
handler procedure with a Canvas_Item parameter; only the general
parameter types gint, guint, event are declared for you (see
gtk-handlers.ads). So you need to instantiate your own. Something
like:

      package Canvas_Item_Marshaller is new Marshallers.Generic_Marshaller
        (Canvas_Item, To_Canvas_Item);

You have to write "To_Canvas_Item" as well; see gtk-arguments.ads, .adb.

Then you can do:

Canvas_Cb.Object_Connect 
    (Canvas,
     "item_selected",
     Canvas_Item_Marshaller.To_Marshaller (Item_Select'Access), 
     Canvas);

Yes, this is confusing!

-- 
-- Stephe