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

Thomas Harning Jr. harningt at gmail.com
Mon Jun 6 16:56:46 EDT 2005

Thomas Harning Jr. wrote:
> Thomas Harning Jr. wrote:
> ...
>>>I've found that calling .Ref() on the Pixbuf will save it, andso
>>>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).
> ...
> I think I may have found the culprit... I had a thread that was
> setting values in the Treestore that called upon the TreeView to
> update through the ThreadNotify method... thinking that the
> TreeStore wasn't 'quite' GUI-enough to need thread-protection.  But
> it seems that way.
> I removed all reference preservation and the .Ref() from the Pixbuf
> as well as columns and such... and there are no more crashes.
> I'll keep my eye open for this occurring in the future, however.

Well the virtually untraceable error has come back.
I got GDB to trace it... and the highest point on the stack is
g_timeout_funcs  in libglib-2.0.so.0
[there are 4 more stack elements above it, but they won't resolve w/
mono via mono_print_method_from_ip.]

I've tried to run mono --debug   with GDB.... and the application
runs fine.  Strangely.. without GDB, mono --debug almost instantly
crashes out w/ NRE.

The thing I added which seems to have retriggered the NRE problems
is using a single-column TreeStore and using callbacks to get the
value for the other columns by referencing the object inside the
The callbacks are preserved in instance variables so they don't get
collected (which is apparently an issue in passing callbacks to GTK#).

Thomas Harning Jr.
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