Code without effect (wx demo TreeCtrl.py ImageList)

[Martin Drautzburg]

In the wx demoy TreeCtrl.py I find the following code, that should
have no effect but seems to be needed nevertheless.

class TestTreeCtrlPan el(wx.Panel):
def __init__(self, parent, log):
[...}
self.tree = MyTreeCtrl(self , tID, wx.DefaultPosit ion, ...
isz = (16,16)
il = wx.ImageList(is z[0], isz[1])
fldridx = il.Add(wx.ArtPr ovider_GetBitma p(wx.ART_FOLDER , wx.ART...
[...]

self.tree.SetIm ageList(il)
--> self.il = il

What is the effect of the last statement? self.il is not used
anywhere. I used similar code in my application and it crashes unless
I assign the image list to the parent panel. The name of the attribute
does not seem to matter. I can write self.foo=il just as well, but
without it it crashes.

[Steve Holden]

Re: Code without effect (wx demo TreeCtrl.py ImageList)

Martin Drautzburg wrote:
[color=blue]
> In the wx demoy TreeCtrl.py I find the following code, that should
> have no effect but seems to be needed nevertheless.
>
> class TestTreeCtrlPan el(wx.Panel):
> def __init__(self, parent, log):
> [...}
> self.tree = MyTreeCtrl(self , tID, wx.DefaultPosit ion, ...
> isz = (16,16)
> il = wx.ImageList(is z[0], isz[1])
> fldridx = il.Add(wx.ArtPr ovider_GetBitma p(wx.ART_FOLDER , wx.ART...
> [...]
>
> self.tree.SetIm ageList(il)
> --> self.il = il
>
> What is the effect of the last statement? self.il is not used
> anywhere. I used similar code in my application and it crashes unless
> I assign the image list to the parent panel. The name of the attribute
> does not seem to matter. I can write self.foo=il just as well, but
> without it it crashes.[/color]

You will probably find that without that reference to the image list it
will be garbage-collected while the images are still beign displayed,
leading to results that are at best unpredictable and at worst fatal to
your program.

regards
Steve
--
Steve Holden http://www.holdenweb.com/
Python Web Programming http://pydish.holdenweb.com/
Holden Web LLC +1 703 861 4237 +1 800 494 3119

[Paul McGuire]

Re: Code without effect (wx demo TreeCtrl.py ImageList)

"Martin Drautzburg" <martin.drautzb urg@web.de> wrote in message
news:87llbtjujx .fsf@web.de...[color=blue]
> In the wx demoy TreeCtrl.py I find the following code, that should
> have no effect but seems to be needed nevertheless.
>
> class TestTreeCtrlPan el(wx.Panel):
> def __init__(self, parent, log):
> [...}
> self.tree = MyTreeCtrl(self , tID, wx.DefaultPosit ion, ...
> isz = (16,16)
> il = wx.ImageList(is z[0], isz[1])
> fldridx = il.Add(wx.ArtPr ovider_GetBitma p(wx.ART_FOLDER , wx.ART...
> [...]
>
> self.tree.SetIm ageList(il)
> --> self.il = il
>
> What is the effect of the last statement? self.il is not used
> anywhere. I used similar code in my application and it crashes unless
> I assign the image list to the parent panel. The name of the attribute
> does not seem to matter. I can write self.foo=il just as well, but
> without it it crashes.[/color]

Two possibilities come to mind:
- used by a base class wx.Panel for which you do not have the source
(although if this were the case, I would think the attribute name would be
significant)
- needed to retain a reference handle to the image list, to prevent it from
being garbage collected (kind of far-fetched, but consistent with the "name
it anything you want" behavior)

-- Paul