[Qt-interest] QListWidget increasingly slow

[Josiah Bryan]

Bob Hood wrote:
> I'm looking for some advice here.  I'm using a QListWidget as a log 
> window, and for short output, it's fine.  However, when I get into 
> thousands of lines, it slowly grinds my application to halt as lines are 
> added to it.
> 
> I know the culprit, though.  I've narrowed it down to the 
> setCurrentRow() method:
> 
>     log_list->addItem(msg);
>     log_list->setCurrentRow(log_list->count() - 1);
> 
> I am using setCurrentRow() to keep the most recent item in the list 
> visible to the user as entries are added.  If I remove this call, 
> everything runs comparatively smoothly -- but entries being added are 
> not visible unless the user manually drags the scroll bar down.  I've 
> also tried using setCurrentItem() to keep things visible, with the same 
> asymptotic results.
> 
> Is there a more efficient way to keep most-recent entries visible using 
> QListWidget?  I'm using QListWidget so I can colorize entries, and add 
> icons to the lines, so if there's a better Qt widget for displaying 
> thousands of lines of text that would give me the same features 
> (colorization and icons), then I'd be happy to try it.

Have you thought about using a QTextEdit and using html to colorize the 
lines and add icons? Use the QTextCursor interface to append html to the 
document.

Line with icon html:

<div style='background:red;color:white'><img src=':/data/icon.png'> 
Hello World!</div>

Then just set the viewport's scroll bar position to the bottom when you 
add text.

HTH. Cheers!
-josiah

> 
> Render me gone,                       |||
> Bob                                 ^(===)^
> ---------------------------------oOO--(_)--OOo---------------------------------
>   The brain is a wonderful organ; it starts working the moment you get up in
>   the morning and does not stop until you get to the office.  - /Robert Frost/
> 
> 
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-=-=-=-=-=-=-=-=-=-=-=-=-
Josiah Bryan
Productive Concepts, Inc.
jbryan at pciint.com
(765) 964-6009, ext. 224