View source for OutlineListbox

{{PageHeader|VT OutlineListbox control}}


__TOC__


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{{TipHeader|cOutlineListBox: workaround for the ugly mousewheel-scroll visual effect}}
When scrolling the contents of cOutlineListbox (or any other VT listbox class) using the mousewheel, it shows a very strange and ugly effect.<br>
It seems the contents are scrolled the wrong way initially.<br>


This is caused by Windows on owner-drawn listboxes when the setting for "Smooth-scroll list boxes" is enabled in the performance options.<br>


[[Image:SmoothScrollingSystemSetting.png]]


One way to fix it is to disable this setting, but this is a system wide setting.<br>
Normally it is not a very good idea to fix those issues by having the user to change system wide settings.<br>


Better to fix in our application. To do this we need to override the default Windows behavior and implement custom code to scroll the contents.<br>
This is done by catching the WM_MOUSEWHEEL message, process the data which is passed and perform the scroll by sending WM_VSCROLL to the listbox.


SalExtension library already offers a function to do this.<br>
The sample for this article uses an adapted version, named PALScrollOnWheel<br>
Using this function you can specify how many lines will be scrolled on one wheel-tick:

<pre>
List Box: lbOutline
   Message Actions
      On WM_MOUSEWHEEL
         Call PALScrollOnWheel( hWndItem, wParam, nLinesPerTick )
         Return 0
</pre>


To see the issue and the workaround, have a look at this YouTube video:

{{VideoLink
|URL=https://www.youtube.com/watch?v=U8Nld5JaxhY
|TEXT=cOutlineListbox : ugly mousewheel scrolling (and workaround)
}}


Here you can download the sample:<br>
{{Download
|URL=http://samples.tdcommunity.net/index.php?dir=&file=WIKI_cOutlineListboxScrollFix.zip
|TEXT=WIKI_cOutlineListboxScrollFix.zip
}}



[[Category:Child Objects]]
[[Category:Visual Toolchest]]