Behaviour problems with wx.ListCtrl.SetItemState

David Hughes wrote:
> I think this is MSW only. It's with wx version 2.6.3.2
(possibly there 
> since 2.5) and can be demonstrated by adding the
following code to 
> ListCtrl demo - after line 233  (modified demo files
are also attached)
>  

> 
> which results in:

> OnItemDeselected: 4   <==  Selected item is
immediately deselected

> OnItemSelected: 6, Blue Man Group, Klein Mandelbrot,
New Age  <== 
> Deselected item is re-selected
> OnItem 6 Selected: Veto'd selection   <== which
brings up the dialog again
> OnItemDeselected: 6
> 
> Adding the same code to ListCtrl_virtual (change all
occurrences of  
> "self.list" to "self"), the
unconditional change works OK but there is 
> the same problem after the conditional dialog.

I was about to write that I couldn't reproduce the problem,
but they I 
tried selecting the items with the mouse instead of the
keyboard and 
discovered that it is only an issue when selecting the items
with the 
mouse.  A little more play and I discovered that it only
happens when 
you release the left mouse button.  In fact if you hold the
button down 
and take the cursor outside of the listctrl and then release
it then you 
don't get the problem, so my guess is that the native
control is doing 
something on the left-up event that is
"completing" the selection 
started with the left-down (or something like that.)

I tried catching the EVT_LEFT_UP to try to work around this,
but it 
appears to be being eaten by the native control.  I also
don't see 
anything in the wx code dealing with left up events.

I found that using a wx.FutureCall(100, ...) instead of the
CallAfter 
works, but if the user holds the mouse button down for
longer than a 
tenth of a second they the problem still happens.  Using a
timer much 
longer than that would start to look silly for the normal
clicks.  So 
instead I tried polling with wx.GetMouseState if it is safe
to make the 
selection change, and if not then delay the change again. 
This works well.

         # unconditional change selection from 2 to 4
         if self.currentItem == 2:
             self.log.WriteText("OnItem 2 Selected:
Veto'd selection\n")
             wx.FutureCall(50, self.SelectAndFocus, 2, 4)

         # conditionally change selection from  6 to 8
         if self.currentItem == 6:
             msgbox = wx.MessageDialog(self, 'Select Item 8

instead?','Message', wx.YES_NO)
             if msgbox.ShowModal() == wx.ID_YES:
                 self.log.WriteText("OnItem 6
Selected: Veto'd selection\n")
                 wx.FutureCall(50, self.SelectAndFocus, 6,
8)

         event.Skip()


     def SelectAndFocus(self, oldidx, newidx):
         if wx.GetMouseState().LeftDown():
             wx.FutureCall(50, self.SelectAndFocus, oldidx,
newidx)
         else:
             self.list.Select(oldidx, False)
             self.list.Select(newidx, True)
             self.list.Focus(newidx)


> 
> Should these be reported back to wxWidgets (if they are
reproducible)?
> 

It would probably be a good idea if only to document that
changing the 
selection from within a EVT_LIST_ITEM_SELECTED handler or
immediately 
after the handler executes doesn't work on wxMSW.  I'm not
sure if 
anything can be done to make it work.


-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java
give you jitters?  Relax with wxPython!


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Robin Dunn wrote:

> David Hughes wrote:
>
>> I think this is MSW only. It's with wx version
2.6.3.2 (possibly 
>> there since 2.5) and can be demonstrated by adding
the following code 
>> to ListCtrl demo - after line 233  (modified demo
files are also 
>> attached)
>
>   I was about to write that I couldn't reproduce the
problem, but they 
> I tried selecting the items with the mouse instead of
the keyboard and 
> discovered that it is only an issue when selecting the
items with the 
> mouse.

I should have explored the boundaries of the problem more
thoroughly.

> A little more play and I discovered that it only
happens when you 
> release the left mouse button.  In fact if you hold the
button down 
> and take the cursor outside of the listctrl and then
release it then 
> you don't get the problem, so my guess is that the
native control is 
> doing something on the left-up event that is
"completing" the 
> selection started with the left-down (or something like
that.)
>
> I tried catching the EVT_LEFT_UP to try to work around
this, but it 
> appears to be being eaten by the native control.  I
also don't see 
> anything in the wx code dealing with left up events.
>
> I found that using a wx.FutureCall(100, ...) instead of
the CallAfter 
> works, but if the user holds the mouse button down for
longer than a 
> tenth of a second they the problem still happens. 
Using a timer much 
> longer than that would start to look silly for the
normal clicks.  So 
> instead I tried polling with wx.GetMouseState if it is
safe to make 
> the selection change, and if not then delay the change
again.  This 
> works well.
>
>         # unconditional change selection from 2 to 4
>         if self.currentItem == 2:
>             self.log.WriteText("OnItem 2
Selected: Veto'd selection\n")
>             wx.FutureCall(50, self.SelectAndFocus, 2,
4)
>
>         # conditionally change selection from  6 to 8
>         if self.currentItem == 6:
>             msgbox = wx.MessageDialog(self, 'Select
Item 8 
> instead?','Message', wx.YES_NO)
>             if msgbox.ShowModal() == wx.ID_YES:
>                 self.log.WriteText("OnItem 6
Selected: Veto'd 
> selection\n")
>                 wx.FutureCall(50, self.SelectAndFocus,
6, 8)
>
>         event.Skip()
>
>
>     def SelectAndFocus(self, oldidx, newidx):
>         if wx.GetMouseState().LeftDown():
>             wx.FutureCall(50, self.SelectAndFocus,
oldidx, newidx)
>         else:
>             self.list.Select(oldidx, False)
>             self.list.Select(newidx, True)
>             self.list.Focus(newidx)

A neat work around that's much better than the "flag
and ignore the 
second event" method I've been using.

>> Should these be reported back to wxWidgets (if they
are reproducible)?
>
> It would probably be a good idea if only to document
that changing the 
> selection from within a EVT_LIST_ITEM_SELECTED handler
or immediately 
> after the handler executes doesn't work on wxMSW. 
I'm not sure if 
> anything can be done to make it work.

I'll raise a bug report shortly and will assume you don't
mind if I 
quote or summarise your findings and solution.
--
Regards,
David Hughes


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