DESCRIPTION

The scrollbar command creates a new window (given by the pathName 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 pathName argument. At the time this command is invoked, there must not exist a window named pathName, but pathName'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 a 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 the BINDINGS section below for details.

ELEMENTS

A scrollbar displays five elements, which are referred to in the widget commands 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.

WIDGET COMMAND

The scrollbar command creates a new Tcl command whose name is pathName. This command may be used to invoke various operations on the widget. It has the following general form:

pathName option ?arg arg ...?

pathName 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.

pathName cget option

. Returns the current value of the configuration option given by option. Option may have any of the values accepted by the scrollbar command.

pathName configure ?option? ?value option value ...?

. Query or modify the configuration options of the widget. If no option is specified, returns a list describing all of the available options for pathName (see Tk_ConfigureInfo for information on the format of this list). If option is specified with no value, then the command returns a list describing the one named option (this list will be identical to the corresponding sublist of the value returned if no option is specified). If one or more option-value pairs are specified, then the command modifies the given widget option(s) to have the given value(s); in this case the command returns an empty string. Option may have any of the values accepted by the scrollbar command.

pathName 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.

pathName 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.

pathName get

. Returns the scrollbar settings in the form of a list whose elements are the arguments to the most recent set widget command.

pathName 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.

pathName 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.

SCROLLING COMMANDS

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 Tcl command generated from the scrollbar's -command option. The command may take any of the following forms. In each case, prefix is the contents of the -command option, which usually has a form like “.t”

prefix 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.

prefix 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.

prefix 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.

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 widget command has the following form:

pathName 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 widget command returns a list of four integers, consisting of the totalUnits, windowUnits, firstUnit, and lastUnit values from the last set widget command.

The commands generated by scrollbars also have a different form when the old syntax is being used:

prefix 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 widget command.

The most recent set widget command 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.

EXAMPLE

Create a window with a scrollable text widget:

toplevel .tl
text .tl.t -yscrollcommand {.tl.s set}
scrollbar .tl.s -command {.tl.t yview}
grid .tl.t .tl.s -sticky nsew
grid columnconfigure .tl 0 -weight 1
grid rowconfigure .tl 0 -weight 1

SEE ALSO

KEYWORDS