self is null in notify signal

[dexterdy]

Strange bug that I encountered when connecting to the notify signal. Self is null and thus gives a runtime error when trying to access properties.

  proc makeEditableOnSelect(self: gtk4.ListItem, param: gobject.ParamSpec, label: gtk4.EditableLabel) =
    if self.selected:
      label.setEditable(true)
    else:
      label.setEditable(false)
  item.connect("notify::selected", makeEditableOnSelect, label)

Throws runtime error:

Traceback (most recent call last)
/home/dexterdy/Documents/repos/relmnotes/src/realmnotes.nim(53) realmnotes
/home/dexterdy/Documents/repos/relmnotes/src/realmnotes.nim(51) main
/home/dexterdy/.nimble/pkgs/gintro-#head/gintro/gio.nim(31998) run
/home/dexterdy/.choosenim/toolchains/nim-1.6.10/lib/core/macros.nim(542) connect_for_signal_cdecl_response6
/home/dexterdy/Documents/repos/relmnotes/src/types/observer.nim(25) on_reponse
/home/dexterdy/Documents/repos/relmnotes/src/types/observer.nim(26) =destroy
/home/dexterdy/Documents/repos/relmnotes/src/components/treeView.nim(22) update
/home/dexterdy/.nimble/pkgs/gintro-#head/gintro/gio.nim(24365) append
/home/dexterdy/.choosenim/toolchains/nim-1.6.10/lib/core/macros.nim(548) connect_for_signal_cdecl_notify1
/home/dexterdy/Documents/repos/relmnotes/src/components/treeView.nim(46) makeEditableOnSelect
/home/dexterdy/.nimble/pkgs/gintro-#head/gintro/gtk4.nim(50256) selected
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

I checked with a debugger and a null check. It is null in all cases, without exception

[StefanSalewski]

Thanks for reporting. Notify signal support was indeed added very late, maybe two years ago, and I think it was working still one year ago. But maybe our latest fixes broke it, I will check soon.

[StefanSalewski]

We have an example for the use of notify signal with GtkDropDown in the Nim GTK4 book, and that works fine for me, see https://ssalewski.de/gtkprogramming.html#_listview_columnview_gridview_and_dropdown, DropDown1.nim. GtkDropDown is closely related to GtkListView.

So I assume that you are doing something wrong. For other ListView variants, use of notify::selected may be not that simple, due to the involved bind and setup procs. For further investigations, you may send a minimal working C example, or a minimal Nim example from which you thinks that it may work.

[StefanSalewski]

Actually my guess is, that

item.connect("notify::selected", makeEditableOnSelect, label)

is wrong. I guess connecting to notify::selected should not be done to items, but for the container like a ListView.