unwanted extra height in scrolledpanel within comboPopup

[C M]

I am trying to create a custom control using the wx.combo.ComboPopup; in this case, what I would like to pop up (really, drop down) is a scrolledPanel that holds a column of a variable number of text controls.  [wxPython 2.8.10 or 2.9.x, Python 2.5 or 2.7, Windows XP].

 

If there are only a smallish number of text controls, I would like the height of the popup to be exactly enough to hold all of them—no taller or shorter.

 

If there are many text controls, I would like the popup's height to clip at a maximum height, like ~500px.  And then, in order to see the remainder of the text controls, there will appear scroll bars to allow scrolling down the column.

 

I *almost* have this, but there is an annoying visual glitch:

 

If I use the scrolledPanel and call SetupScrolling() once all text controls are added, it works other than this: there is a small bit of extra space at the end of the column of text controls. 

 

In order to see this, please run the attached "Small Runnable Sample App".  Pop open the combo and scroll down to the very bottom. See that red bit?

 

The question is:  why is the scrolledpanel (in red) showing through and how can I have that not happen?

 

(I have fooled around with how I set the pref_height of the popup but no matter what I try, so far I am never getting it to not show at least some red).

 

Many thanks,

Che

[Robin Dunn]

On 11/9/12 1:23 PM, C M wrote:
> I am trying to create a custom control using the wx.combo.ComboPopup; in
> this case, what I would like to pop up (really, drop down) is a
> scrolledPanel that holds a column of a variable number of text
> controls. [wxPython 2.8.10 or 2.9.x, Python 2.5 or 2.7, Windows XP].
>
> If there are only a smallish number of text controls, I would like the

> height of the popup to be exactly enough to hold all of them�no taller
> or shorter.
>
> If thereare many text controls, I would like the popup's height to clip
> at a maximum height, like ~500px.And then, in order to see the remainder

> of the text controls, there will appear scroll bars to allow scrolling
> down the column.
>
> I *almost* have this, but there is an annoying visual glitch:
>
> If I use the scrolledPanel and call SetupScrolling() once all text
> controls are added, it works other than this: there is a small bit of
> extra space at the end of the column of text controls.
>
> In order to see this, please run the attached "Small Runnable Sample

> App".Pop open the combo and scroll down to the very bottom.See that red bit?

>
> The question is:why is the scrolledpanel (in red) showing through and
> how can I have that not happen?
>

This is a side-effect of how wx.ScrolledWindow (the base class of
ScrolledPanel) works. ScrolledWindows have both virtual size and scroll
rate (among others) attributes that are used to define the scrolling.
The scroll rate is how many pixels the content is scrolled when the
scrollbar's arrow widgets are clicked, this is also called scroll units.
The virtual size will always be rounded up to the next multiple of the
scroll units because the ScrolledWindow is not able to deal with a
fractional unit. If the virtual size is not rounded up then you have
the problem of not being able to scroll far enough to see all of the
content. By rounding up you can see all of it, plus an extra 0 to
scrollRate-1 pixels. Being able to see too much in this case is better
than not being able to see enough.

If being able to use an exact amount of virtual size that is not rounded
up is important to you then you can try using wx.VScrolledWindow instead.


--
Robin Dunn
Software Craftsman
http://wxPython.org