Darren's Weekly Nugget 02/02/2009

[Darren]

Happy Groundhog Day everybody!  From what I heard on the news, the groundhog came out of his burrow and saw a For Loop, which means there will be at least 50 more weeks of nuggets.  Way to go, groundhog!

 Today's nugget involves the Tree Control.  As you may have seen in my first nugget of 2009, my favorite feature of LabVIEW 7.0 was the Tree Control.  One of the problems I always had with the Tree Control was figuring out when to show the scrollbars of the tree.  It was relatively easy to figure out if I needed to show the vertical scrollbar--if there were more visible tree items than there were visible tree rows, show the vertical scrollbar.  Figuring out whether or not to show the horizontal scrollbar, however, was much more difficult.  Here's the hackish procedure I used to use:

1.  Make my front panel take up the entire screen.
2. Make the tree control take up the entire panel width.
3. Grow the visible column all the way to the end of the screen.
4. Shrink the tree back down to normal size.
5. Shrink the panel back down to normal size.

After doing all of this, I would just always show the horizontal scrollbar.  It worked reasonably well, but I always felt kinda dirty using that technique, and most of the time, a horizontal scrollbar was showing when it wasn't necessary.  And it also felt weird that when it was necessary, you would often be able to scroll way past the visible text into empty space.

All of this pain and suffering went away in LabVIEW 8.0.  In 8.0 and later, there is a utility VI in vi.lib\tree called Tree_ShowScrollBar.vi.  Now I just stick this VI after any operation in which I'm adding, removing, editing, or expanding tree items, and it figures out whether or not it needs to show the vertical and horizontal scrollbars for the tree.

-D

P.S. - Check out past nuggets here. 

[RVallieu]

This is a great nugget!

I wish I had found out about this before today.

Thanks.

[Wiebe@CARYA]

Darren,

Great VI, didn't know about it.

If you have a few thousand elements, you might want to make a copy of the
VI, and slightly modify it. For once, it's not password protected... For the
following reason...

If you open it, you'll see it uses DispItems. This does not return all
visible items, but all items that are not under a collapsed parent. Items
that will be visible when you scroll up or down, are also on the list.
DispItems isn't that slow. But the check with Get Text Rect is slow..

So, this list might be large, and when you add one or two items, you don't
want to recheck them again. First, if the horizontal scrollbar (HS) was
visible, why wouldn't it be visible after adding an item? Also, if it is not
visible, why check the items that where in the tree before again? We do want
to check for the HS again if the VS changed though...

I'll send my (completely untested) incremental check soon...

Regards,

Wiebe.

[wiebe@CARYA]

Here it is, now slightly tested...