[Gtk-sharp-list] NullReferenceException issues - suggestion for solutions

Thomas Harning Jr. harningt at gmail.com
Mon Jun 6 15:01:41 EDT 2005

I've run into NRE's semi-randomly when using GTK#,
which I think is due to Garbage collection of things that have been
added to an object.
 I create a pixbuf, run some transforms, disposing all temporaries
leaving behind a non-disposed Pixbuf.
 I use that generated Pixbuf in a TreeStore for a TreeView.
 If I force the app to redraw many times/cause a GC by dragging
windows on top of it or moving the window itself, a NRE gets thrown
from within the gtk_main loop.
 I've found that calling .Ref() on the Pixbuf will save it, and so
will adding that pixbuf to an arraylist to preserve a reference to it.
* This is a HORRIBLE kludge and I'm not even sure if it fixes it
permanently (it stops the NRE in the short-run).

It would be good if this were fixed and/or proper documentation on
how to properly work around the issue.

I would think that the TreeStore would be smart enough to increment
the reference count when the Pixbuf is added to the list.  I'm
thinkin' that's a potential underlying issue that's causing many

Also... when I create a window via Window w = new Window() {well.. a
sub-class that handles preloading data, no other instance data}.
Would the destruction of the Window instance via the GC cause any
issues?  It would greatly make UI developing a pain when there is
instance data, like using Glade# and AutoConnect-ing instances.

So... basically... I want some sort of Guide for dealing with the GC
environment and GTK#... or a super-fix that will keep objects around
if they are referenced somehow in unmanaged code. (Now that I think
of it, replacing IntPtr with Handle fixes that.... I think.. not
sure, I'll see how that works).  [I think it works by holding a
reference to the parent object... but... isn't the GC suppose to
handle circular references and clean up stuff like this?]

Thomas Harning Jr.
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