Checkbutton

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

Tk::Checkbutton - Create and manipulate Checkbutton widgets

SYNOPSIS

$checkbutton = $parent->Checkbutton(?options?);

STANDARD OPTIONS

-activebackground -activeforeground -anchor -background -bitmap -borderwidth -compound -cursor -disabledforeground -font -foreground -highlightbackground -highlightcolor -highlightthickness -image -justify -padx -pady -relief -takefocus -text -textvariable -underline -wraplength

See Tk::options for details of the standard options.

WIDGET-SPECIFIC OPTIONS

Name: command
Class: Command
Switch: -command: Specifies a perl/Tk callback to associate with the button. This command is typically invoked when mouse button 1 is released over the button window. The button's global variable (-variable option) will be updated before the command is invoked.
Name: height
Class: Height
Switch: -height: Specifies a desired height for the button. If an image or bitmap is being displayed in the button then the value is in screen units (i.e. any of the forms acceptable to Tk_GetPixels); for text it is in lines of text. If this option isn't specified, the button's desired height is computed from the size of the image or bitmap or text being displayed in it.
Name: indicatorOn
Class: IndicatorOn
Switch: -indicatoron: Specifies whether or not the indicator should be drawn. Must be a proper boolean value. If false, the relief option is ignored and the widget's relief is always sunken if the widget is selected and raised otherwise.
Command-Line Name: -offrelief
Database Name: offRelief
Database Class: OffRelief: Specifies the relief for the checkbutton when the indicator is not drawn and the checkbutton is off. The default value is raised. By setting this option to flat and setting -indicatoron false -overrelief raised, the effect is achieved of having a flat button that raises on mouse-over and which is depressed when activated. This is the behavior typically exhibited by the Bold, Italic, and Underline checkbuttons on the toolbar of a word-processor, for example.
Name: offValue
Class: Value
Switch: -offvalue: Specifies value to store in the button's associated variable whenever this button is deselected. Defaults to ``0''.
Name: onValue
Class: Value
Switch: -onvalue: Specifies value to store in the button's associated variable whenever this button is selected. Defaults to ``1''.
Command-Line Name: -overrelief
Database Name: overRelief
Database Class: OverRelief: Specifies an alternative relief for the button, to be used when the mouse cursor is over the widget. This option can be used to make toolbar buttons, by configuring -relief flat -overrelief raised. If the value of this option is the empty string, then no alternative relief is used when the mouse cursor is over the button. The empty string is the default value.
Name: selectColor
Class: Background
Switch: -selectcolor: Specifies a background color to use when the button is selected. If indicatorOn is true then the color applies to the indicator. Under Windows, this color is used as the background for the indicator regardless of the select state. If indicatorOn is false, this color is used as the background for the entire widget, in place of background or activeBackground, whenever the widget is selected. If specified as an empty string then no special color is used for displaying when the widget is selected.
Name: selectImage
Class: SelectImage
Switch: -selectimage: Specifies an image to display (in place of the image option) when the checkbutton is selected. This option is ignored unless the image option has been specified.
Name: state
Class: State
Switch: -state: Specifies one of three states for the checkbutton: normal, active, or disabled. In normal state the checkbutton is displayed using the foreground and background options. The active state is typically used when the pointer is over the checkbutton. In active state the checkbutton is displayed using the activeForeground and activeBackground options. Disabled state means that the checkbutton should be insensitive: the default bindings will refuse to activate the widget and will ignore mouse button presses. In this state the disabledForeground and background options determine how the checkbutton is displayed.
Name: variable
Class: Variable
Switch: -variable: Specifies reference to a variable to set to indicate whether or not this button is selected. Defaults to "\$widget->{'Value'}" member of the widget's hash. In general perl variables are "undef" unless specifically initialized which will not match either default -onvalue or default -offvalue.
Name: width
Class: Width
Switch: -width: Specifies a desired width for the button. If an image or bitmap is being displayed in the button then the value is in screen units (i.e. any of the forms acceptable to Tk_GetPixels); for text it is in characters. If this option isn't specified, the button's desired width is computed from the size of the image or bitmap or text being displayed in it.

DESCRIPTION

The Checkbutton method creates a new window (given by the $widget argument) and makes it into a checkbutton widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the checkbutton such as its colors, font, text, and initial relief. The checkbutton 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 checkbutton is a widget that displays a textual string, bitmap or image and a square called an indicator. If text is displayed, it must all be in a single font, but it can occupy multiple lines on the screen (if it contains newlines or if wrapping occurs because of the wrapLength option) and one of the characters may optionally be underlined using the underline option. A checkbutton has all of the behavior of a simple button, including the following: it can display itself in either of three different ways, according to the state option; it can be made to appear raised, sunken, or flat; it can be made to flash; and it invokes a perl/Tk callback whenever mouse button 1 is clicked over the checkbutton.

In addition, checkbuttons can be selected. If a checkbutton is selected then the indicator is normally drawn with a selected appearance, and a Tcl variable associated with the checkbutton is set to a particular value (normally 1). Under Unix, the indicator is drawn with a sunken relief and a special color. Under Windows, the indicator is drawn with a check mark inside. If the checkbutton is not selected, then the indicator is drawn with a deselected appearance, and the associated variable is set to a different value (typically 0). Under Unix, the indicator is drawn with a raised relief and no special color. Under Windows, the indicator is drawn without a check mark inside. By default, the name of the variable associated with a checkbutton is the same as the name used to create the checkbutton. The variable name, and the ``on'' and ``off'' values stored in it, may be modified with options on the command line or in the option database. Configuration options may also be used to modify the way the indicator is displayed (or whether it is displayed at all). By default a checkbutton is configured to select and deselect itself on alternate button clicks. In addition, each checkbutton monitors its associated variable and automatically selects and deselects itself when the variables value changes to and from the button's ``on'' value.

WIDGET METHODS

The Checkbutton 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 checkbutton widgets:

$checkbutton->deselect: Deselects the checkbutton and sets the associated variable to its ``off'' value.
$checkbutton->flash: Flashes the checkbutton. This is accomplished by redisplaying the checkbutton several times, alternating between active and normal colors. At the end of the flash the checkbutton is left in the same normal/active state as when the command was invoked. This command is ignored if the checkbutton's state is disabled.
$checkbutton->invoke: Does just what would have happened if the user invoked the checkbutton with the mouse: toggle the selection state of the button and invoke the perl/Tk callback associated with the checkbutton, if there is one. The return value is the return value from the perl/Tk callback, or an empty string if there is no command associated with the checkbutton. This command is ignored if the checkbutton's state is disabled.
$checkbutton->select: Selects the checkbutton and sets the associated variable to its ``on'' value.
$checkbutton->toggle: Toggles the selection state of the button, redisplaying it and modifying its associated variable to reflect the new state.

BINDINGS

Tk automatically creates class bindings for checkbuttons that give them the following default behavior:

[1]

On Unix systems, a checkbutton activates whenever the mouse passes over it and deactivates whenever the mouse leaves the checkbutton. On Mac and Windows systems, when mouse button 1 is pressed over a checkbutton, the button activates whenever the mouse pointer is inside the button, and deactivates whenever the mouse pointer leaves the button.

[2]

When mouse button 1 is pressed over a checkbutton, it is invoked (its selection state toggles and the command associated with the button is invoked, if there is one).

[3]

When a checkbutton has the input focus, the space key causes the checkbutton to be invoked. Under Windows, there are additional key bindings; plus (+) and equal (=) select the button, and minus (-) deselects the button.

If the checkbutton's state is disabled then none of the above actions occur: the checkbutton is completely non-responsive.

The behavior of checkbuttons can be changed by defining new bindings for individual widgets or by redefining the class bindings.

KEYWORDS

checkbutton, widget