Scrolling Commands
- Preface
- Introduction
- Tutorial
- Implementation
- Commands
- bitmap
- eval-wish
- get-tk-var
- photo
- set-tk-var!
- tk
- tk-id->widget
- tk-var
- tk/after
- tk/appname
- tk/bind
- tk/bindtags
- tk/caret
- tk/choosecolor
- tk/choosedirectory
- tk/clipboard
- tk/console
- tk/destroy
- tk/dialog
- tk/event
- tk/focus
- tk/getopenfile
- tk/getsavefile
- tk/grab
- tk/grid
- tk/image
- tk/lower
- tk/messagebox
- tk/option
- tk/pack
- tk/place
- tk/popup
- tk/raise
- tk/scaling
- tk/update
- tk/useinputmethods
- tk/wait
- tk/windowingsystem
- tk/winfo
- tk/wm
- Options
- Extensions
- Changes
When the user interacts with the scrollbar, for example by dragging the slider, the scrollbar notifies the associated widget that it must change its view. The scrollbar makes the notification by evaluating a command generated from the scrollbar's #:command option. The command may take any of the following forms. In each case, (#<widget> 'yview) is used as an example for the contents of the #:command option.
(#<widget> 'yview 'moveto fraction)
Fraction is a real number between 0 and 1. The widget should adjust its view so that the point given by fraction appears at the beginning of the widget. If fraction is 0 it refers to the beginning of the document. 1.0 refers to the end of the document, 0.333 refers to a point one-third of the way through the document, and so on.
(#<widget> 'yview 'scroll number units)
The widget should adjust its view by number units. The units are defined in whatever way makes sense for the widget, such as characters or lines in a text widget. Number is either 1, which means one unit should scroll off the top or left of the window, or -1, which means that one unit should scroll off the bottom or right of the window.
(#<widget> 'yview 'scroll number pages)
The widget should adjust its view by number pages. It is up to the widget to define the meaning of a page; typically it is slightly less than what fits in the window, so that there is a slight overlap between the old and new views. Number is either 1, which means the next page should become visible, or -1, which means that the previous page should become visible.