Re: scroll-wheel problems with an owner-draw ListBox
From: me (me_at_here.com)
Date: 01/15/05
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Date: Sat, 15 Jan 2005 18:14:08 +0000 (UTC)
Doug, you've diagnosed my problem exactly!
Many thanks,
Karl.
"Doug Harrison [MVP]" <dsh@mvps.org> wrote in message
news:edtgu01mefi41u9m4qf5ke0vil86ivrutq@4ax.com...
> me wrote:
>
>>Hi, i've written an owner-draw ListBox but I get some strange effects when
>>using the scroll-wheel to scroll the window.
>>
>>If I set the type to "Fixed" the scroll-wheel causes the window to scroll
>>correctly but for some reason my MeasureItem function never gets called
>>and
>>the items in the listbox are the wrong height (they just use some kind of
>>default value).
>>
>>If I set the type to "Variable" the MeasureItem function gets called for
>>every item as expected and the listbox looks correct (all items are the
>>correct height). But when I use the scroll-wheel to scroll the window it
>>always scrolls downwards one whole page before stopping at the correct
>>window position.
>>
>>A friend said that he might have seen this scroll behavior on some other
>>windows applications - is this a known problem? How come my MeasureItem
>>function doesn't get called (not even once) when the owner-draw type is
>>set
>>to "Fixed"?
>>
>>Is there a function I can call to set the "fixed" height manually?
>>
>>Any help greatly appreciated!
>
> Below are excerpts from some past messages I've written on these topics:
>
> ***** About LBS_OWNERDRAWFIXED
>
> You can set LBS_OWNERDRAWFIXED in the
> resource editor, ignore the initial WM_MEASUREITEM sent to your dialog
> box, and fix things up in OnInitDialog with CListBox::SetItemHeight.
> Windows appears to reliably provide a default height for
> WM_MEASUREITEM, but if you feel really strongly about setting it, you
> can override your dialog class's WindowProc and handle the message
> there.
>
> In my OnInitDialog handlers, I have code that sets the height using that
> SetItemHeight and follows it by a function that resizes the listbox if the
> "integral height" style is set. So I need to use two extra function calls
> to
> make LBS_OWNERDRAWFIXED work right.
>
> ***** About funky listbox animation
>
> I'd avoid LBS_OWNERDRAWVARIABLE if possible, as it suffers a weird bug in
> Win2K and XP, when "smooth scrolling of listboxes" is activated (TweakUI
> calls it "Enable list box animation"), in which rolling the wheel causes
> the listbox to visually scroll in the "opposite" direction though the
> right
> item is brought into view. A user reported this in one of my apps, and I
> cured it by switching to LBS_OWNERDRAWFIXED. See this message for another
> report by a C# user:
>
> http://groups.google.com/groups?selm=v8n7sqjq14k41a%40corp.supernews.com
>
> --
> Doug Harrison
> Microsoft MVP - Visual C++
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