Re: [Vala] Houston we have a problem(gtk.builder signals not functioning)

[Frederik <scumm_fredo gmx net>]

Am 08.04.2010 20:30, Karl Zollner wrote:
> I have been a lurker here for a while and noticed a number of other posts
> drawing attention to difficulties getting signals from glade-3(.ui xml
> files) to work with handlers defined in ones source code.
>
> This problem is now official. Signals are not getting properly connected. I
> use the word official because I have tried this on multiple different
> machines, real and vms, with different versions of vala and glade-3
> (including git current vala and glade-3). And in no combination does
> build.connect_signals actually result in a working program- in most cases
> error message just reports 'cannot find blah-blah-on-button-clicked signal',
> but in other case there is just an abrupt segmentaion fault.

There are 3 common error sources when using Gtk.Builder with Vala, your problem
is probably related to one of them:

1) Forgetting to use [CCode (instance_pos = -1)] when using instance
   methods instead of static methods as handlers

2) Forgetting to mangle the handler method names in Glade, e.g. from
   'FooBar.my_handler' to 'foo_bar_my_handler'

3) Not using the right signature for the handler. One missing parameter
   or one parameter to much will result in a segmentation fault. If the
   signal signature is

     public class Area : Object {
         public signal void clicked (int x, int y);
     }

   then the handler method must have *exactly* these parameters in order
   to work with Gtk.Builder's auto-connect:

     [CCode (instance_pos = -1)]
     public void on_clicked (Area source, int x, int y) { }

   Vala can't recognize this mistake, because auto-connection happens at
   runtime an it doesn't know at compile-time which method will be connected
   to which signal.

One solution to make auto-connection more type safe and more convenient to
use could be to introduce a new attribute in Vala, something like:

  [AutoConnectHandler (signal = "Area.clicked")]
  public void on_clicked (Area source, int x, int y) { }

so that Vala could do a method signature check at compile-time.


Best regards,

Frederik