NAME¶
Tk::Scrollbar - Create and manipulate Scrollbar widgets
SYNOPSIS¶
$scrollbar =
$parent->
Scrollbar(?
options?);
STANDARD OPTIONS¶
-activebackground -highlightbackground -orient -takefocus
-background -highlightcolor -relief -troughcolor
-borderwidth -highlightthickness -repeatdelay
-cursor -jump -repeatinterval
See Tk::options for details of the standard options.
- Name: activeRelief
- Class: ActiveRelief
- Switch: -activerelief
- Specifies the relief to use when displaying the element
that is active, if any. Elements other than the active element are always
displayed with a raised relief.
- Name: command
- Class: Command
- Switch: -command
- Specifies a callback to invoke to change the view in the
widget associated with the scrollbar. When a user requests a view change
by manipulating the scrollbar, the callback is invoked. The callback is
passed additional arguments as described later. This option almost always
has a value such as [xview => $widget] or
[yview => $widget], consisting of the a widget
object and either xview (if the scrollbar is for horizontal
scrolling) or yview (for vertical scrolling). All scrollable
widgets have xview and yview methods that take exactly the
additional arguments appended by the scrollbar as described in
"SCROLLING COMMANDS" below.
- Name: elementBorderWidth
- Class: BorderWidth
- Switch: -elementborderwidth
- Specifies the width of borders drawn around the internal
elements of the scrollbar (the two arrows and the slider). The value may
have any of the forms acceptable to Tk_GetPixels. If this value is
less than zero, the value of the borderWidth option is used in its
place.
- Name: width
- Class: Width
- Switch: -width
- Specifies the desired narrow dimension of the scrollbar
window, not including 3-D border, if any. For vertical scrollbars this
will be the width and for horizontal scrollbars this will be the height.
The value may have any of the forms acceptable to
Tk_GetPixels.
DESCRIPTION¶
The
Scrollbar method creates a new window (given by the $widget argument)
and makes it into a scrollbar widget. Additional options, described above, may
be specified on the command line or in the option database to configure
aspects of the scrollbar such as its colors, orientation, and relief. The
scrollbar command returns its $widget argument. At the time this
command is invoked, there must not exist a window named $widget, but $widget's
parent must exist.
A scrollbar is a widget that displays two arrows, one at each end of the
scrollbar, and a
slider in the middle portion of the scrollbar. It
provides information about what is visible in an
associated window that
displays an document of some sort (such as a file being edited or a drawing).
The position and size of the slider indicate which portion of the document is
visible in the associated window. For example, if the slider in a vertical
scrollbar covers the top third of the area between the two arrows, it means
that the associated window displays the top third of its document.
Scrollbars can be used to adjust the view in the associated window by clicking
or dragging with the mouse. See "BINDINGS" below for details.
ELEMENTS¶
A scrollbar displays five elements, which are referred to in the methods for the
scrollbar:
- arrow1
- The top or left arrow in the scrollbar.
- trough1
- The region between the slider and arrow1.
- slider
- The rectangle that indicates what is visible in the
associated widget.
- trough2
- The region between the slider and arrow2.
- arrow2
- The bottom or right arrow in the scrollbar.
The
Scrollbar method creates a widget object. This object supports the
configure and
cget methods described in Tk::options which can be
used to enquire and modify the options described above. The widget also
inherits all the methods provided by the generic Tk::Widget class.
The following additional methods are available for scrollbar widgets:
- $scrollbar->activate(?element?)
- Marks the element indicated by element as active,
which causes it to be displayed as specified by the
activeBackground and activeRelief options. The only element
values understood by this command are arrow1, slider, or
arrow2. If any other value is specified then no element of the
scrollbar will be active. If element is not specified, the command
returns the name of the element that is currently active, or an empty
string if no element is active.
- $scrollbar->delta(deltaX,
deltaY)
- Returns a real number indicating the fractional change in
the scrollbar setting that corresponds to a given change in slider
position. For example, if the scrollbar is horizontal, the result
indicates how much the scrollbar setting must change to move the slider
deltaX pixels to the right (deltaY is ignored in this case).
If the scrollbar is vertical, the result indicates how much the scrollbar
setting must change to move the slider deltaY pixels down. The
arguments and the result may be zero or negative.
- $scrollbar->fraction(x,
y)
- Returns a real number between 0 and 1 indicating where the
point given by x and y lies in the trough area of the
scrollbar. The value 0 corresponds to the top or left of the trough, the
value 1 corresponds to the bottom or right, 0.5 corresponds to the middle,
and so on. X and y must be pixel coordinates relative to the
scrollbar widget. If x and y refer to a point outside the
trough, the closest point in the trough is used.
- $scrollbar->get
- Returns the scrollbar settings in the form of a list whose
elements are the arguments to the most recent set method.
- $scrollbar->identify(x,
y)
- Returns the name of the element under the point given by
x and y (such as arrow1), or an empty string if the
point does not lie in any element of the scrollbar. X and y
must be pixel coordinates relative to the scrollbar widget.
- $scrollbar->set(first,
last)
- This command is invoked by the scrollbar's associated
widget to tell the scrollbar about the current view in the widget. The
command takes two arguments, each of which is a real fraction between 0
and 1. The fractions describe the range of the document that is visible in
the associated widget. For example, if first is 0.2 and last
is 0.4, it means that the first part of the document visible in the window
is 20% of the way through the document, and the last visible part is 40%
of the way through.
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 callback specified as the
scrollbar's
-command option. The callback may take several forms. In
each case, the intial arguments passed are those specified in the
-command callback itself, which usually has a form like [
yview
=>
$widget]. (Which will invoke
$widget->
yview(...) where the ... part is as
below. See Tk::callbacks for details.) The callback is passed additional
arguments as follows:
- 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.
- 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.
- scroll,number,page
- 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.
OLD COMMAND SYNTAX¶
In versions of Tk before 4.0, the
set and
get widget commands used
a different form. This form is still supported for backward compatibility, but
it is deprecated. In the old command syntax, the
set method has the
following form:
- $scrollbar->set(totalUnits,
windowUnits, firstUnit, lastUnit)
- In this form the arguments are all integers.
TotalUnits gives the total size of the object being displayed in
the associated widget. The meaning of one unit depends on the associated
widget; for example, in a text editor widget units might correspond to
lines of text. WindowUnits indicates the total number of units that
can fit in the associated window at one time. FirstUnit and
lastUnit give the indices of the first and last units currently
visible in the associated window (zero corresponds to the first unit of
the object).
Under the old syntax the
get method returns a list of four integers,
consisting of the
totalUnits,
windowUnits,
firstUnit, and
lastUnit values from the last
set method.
The callbacks generated by scrollbars also have a different form when the old
syntax is being used, the callback is passed a single argument:
- unit
- Unit is an integer that indicates what should appear
at the top or left of the associated widget's window. It has the same
meaning as the firstUnit and lastUnit arguments to the
set method.
The most recent
set method determines whether or not to use the old
syntax. If it is given two real arguments then the new syntax will be used in
the future, and if it is given four integer arguments then the old syntax will
be used.
BINDINGS¶
Tk automatically creates class bindings for scrollbars that give them the
following default behavior. If the behavior is different for vertical and
horizontal scrollbars, the horizontal behavior is described in parentheses.
- [1]
- Pressing button 1 over arrow1 causes the view in the
associated widget to shift up (left) by one unit so that the document
appears to move down (right) one unit. If the button is held down, the
action auto-repeats.
- [2]
- Pressing button 1 over trough1 causes the view in
the associated widget to shift up (left) by one screenful so that the
document appears to move down (right) one screenful. If the button is held
down, the action auto-repeats.
- [3]
- Pressing button 1 over the slider and dragging causes the
view to drag with the slider. If the jump option is true, then the
view doesn't drag along with the slider; it changes only when the mouse
button is released.
- [4]
- Pressing button 1 over trough2 causes the view in
the associated widget to shift down (right) by one screenful so that the
document appears to move up (left) one screenful. If the button is held
down, the action auto-repeats.
- [5]
- Pressing button 1 over arrow2 causes the view in the
associated widget to shift down (right) by one unit so that the document
appears to move up (left) one unit. If the button is held down, the action
auto-repeats.
- [6]
- If button 2 is pressed over the trough or the slider, it
sets the view to correspond to the mouse position; dragging the mouse with
button 2 down causes the view to drag with the mouse. If button 2 is
pressed over one of the arrows, it causes the same behavior as pressing
button 1.
- [7]
- If button 1 is pressed with the Control key down, then if
the mouse is over arrow1 or trough1 the view changes to the
very top (left) of the document; if the mouse is over arrow2 or
trough2 the view changes to the very bottom (right) of the
document; if the mouse is anywhere else then the button press has no
effect.
- [8]
- In vertical scrollbars the Up and Down keys have the same
behavior as mouse clicks over arrow1 and arrow2,
respectively. In horizontal scrollbars these keys have no effect.
- [9]
- In vertical scrollbars Control-Up and Control-Down have the
same behavior as mouse clicks over trough1 and trough2,
respectively. In horizontal scrollbars these keys have no effect.
- [10]
- In horizontal scrollbars the Up and Down keys have the same
behavior as mouse clicks over arrow1 and arrow2,
respectively. In vertical scrollbars these keys have no effect.
- [11]
- In horizontal scrollbars Control-Up and Control-Down have
the same behavior as mouse clicks over trough1 and trough2,
respectively. In vertical scrollbars these keys have no effect.
- [12]
- The Prior and Next keys have the same behavior as mouse
clicks over trough1 and trough2, respectively.
- [13]
- The Home key adjusts the view to the top (left edge) of the
document.
- [14]
- The End key adjusts the view to the bottom (right edge) of
the document.
SEE ALSO¶
Tk::callbacks Tk::Scrolled
KEYWORDS¶
scrollbar, widget