# Ruby/Tk: how to get Scrollbar to stay scrolled?

**URL:** <https://www.ruby-forum.com/t/ruby-tk-how-to-get-scrollbar-to-stay-scrolled/161531>\
**Category:** Ruby\
**Created:** [February 27, 2009, 4:51am UTC](https://www.ruby-forum.com/t/ruby-tk-how-to-get-scrollbar-to-stay-scrolled/161531 "2009-02-27T04:51:58Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![cruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8dc957/32.png) [@cruby](https://www.ruby-forum.com/u/cruby)\
**Post date:** [February 27, 2009, 4:51am UTC](https://www.ruby-forum.com/t/ruby-tk-how-to-get-scrollbar-to-stay-scrolled/161531/1 "2009-02-27T04:51:58Z")

</div>

Hello all,

I am trying to get a new grid control working (similar to a TreeView  
without the tree) and my most recent problem is to get the Scrollbar to  
respond to the changes it initiates in the grid. I’ve tried a few  
things, but nothing on the web seems to deal with getting a Scrollbar to  
work with anything that isn’t already inside Tk and has the correct  
hooks. The closest I’ve come is some allusions at

> **[TkDocs Tutorial](https://tkdocs.com/tutorial/onepage.html)**
>
> Modern Tk Tutorial for Python, Tcl, Ruby, and Perl

The code I was trying includes this just after the widgets are setup:

@v\_scroll.command proc{|\*args| self.yview(\*args)}

# self.yscrollcommand proc{|\*args| @v\_scroll.set(\*args)}

self.yscrollcommand proc{|\*args|  
@v\_scroll.set(@y\_scroll\_start\_fraction, @y\_scroll\_end\_fraction)}

The scrollbar responds since I defined yview to send to internal  
yviewMoveTo and yviewScroll methods (as I found somewhere else): the  
move commands are sent to the correct methods. However once the user  
releases the scrollbar, the scrollbar always returns to the original  
position (top).

I tried defining it the same as in existing widgets, eg:  
def yscrollcommand block  
configure\_cmd ‘yscrollcommand’, block  
self  
end

But even if I include TkConfigMethod and TkComm in the class, it can’t  
figure out what TkConfigMethod’s path is (and I certainly don’t know).  
I also tried some other things like using the standard \*args version  
above and have this definition of yscrollcommand:

block.call(@y\_scroll\_start\_fraction, @y\_scroll\_end\_fraction)

But apparently I am missing some deeper understanding of what the  
process is here… Since yscrollcommand seems to only be called at the  
start, I figure the contents have to be linking a block to something  
else, but the definitions in tk.rb didn’t clear anything up for me. It  
seems like a lot of code acrobatics behind configure\_cmd() - do I need  
that?

Has anyone been successful at this or can tell me what I should be  
trying instead?

Thanks!

-Chris

---

<div class="post-metadata">

**Author:** ![cruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8dc957/32.png) [@cruby](https://www.ruby-forum.com/u/cruby)\
**Post date:** [February 27, 2009, 7:14am UTC](https://www.ruby-forum.com/t/ruby-tk-how-to-get-scrollbar-to-stay-scrolled/161531/2 "2009-02-27T07:14:21Z")

</div>

Sorry for replying to myself, but I just stumbled on a possible  
solution: using the typical  
@v\_scroll.set(@first\_viz,@last\_viz)  
at the end of the yview() declaration. In my few trials it seems to  
work even though it doesn’t fit in the prescribed callback mechanism  
that every book and website describes. Which, incidentally, is why I  
didn’t think of it sooner.

Does this add a problem that will bite me later?