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### 2.7 checkbutton

checkbutton \- Create and manipulate check-button widgets

#### Synopsis

checkbutton pathName ?options?

#### Standard Options

    activeBackground  bitmap              font        relief
    activeForeground  borderWidth         foreground  text
    anchor            cursor              padX        textVariable
    background        disabledForeground  padY

See options, for more information.

#### Arguments for Checkbutton

`:command`

  Name=`"command" Class=`"`Command"`

  Specifies a Tcl command 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.

`:height`

  Name=`"height" Class=`"`Height"`

  Specifies a desired height for the button. If a 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 bitmap or text being displayed in it.

`:offvalue`

  Name=`"offValue" Class=`"`Value"`

  Specifies value to store in the button’s associated variable whenever this button is deselected. Defaults to “0”.

`:onvalue`

  Name=`"onValue" Class=`"`Value"`

  Specifies value to store in the button’s associated variable whenever this button is selected. Defaults to “1”.

`:selector`

  Name=`"selector" Class=`"`Foreground"`

  Specifies the color to draw in the selector when this button is selected. If specified as an empty string then no selector is drawn for the button.

`:state`

  Name=`"state" Class=`"`State"`

  Specifies one of three states for the check button: normal, active, or disabled. In normal state the check button is displayed using the foreground and background options. The active state is typically used when the pointer is over the check button. In active state the check button is displayed using the activeForeground and activeBackground options. Disabled state means that the check button is insensitive: it doesn’t activate and doesn’t respond to mouse button presses. In this state the disabledForeground and background options determine how the check button is displayed.

`:variable`

  Name=`"variable" Class=`"`Variable"`

  Specifies name of global variable to set to indicate whether or not this button is selected. Defaults to the name of the button within its parent (i.e. the last element of the button window’s path name).

`:width`

  Name=`"width" Class=`"`Width"`

  Specifies a desired width for the button. If a 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 bitmap or text being displayed in it.

#### Description

The checkbutton command creates a new window (given by the pathName argument) and makes it into a check-button widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the check button such as its colors, font, text, and initial relief. The checkbutton 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 check button is a widget that displays a textual string or bitmap and a square called a selector. A check button 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 Tcl command whenever mouse button 1 is clicked over the check button.

In addition, check buttons can be selected. If a check button is selected then a special highlight appears in the selector, and a Tcl variable associated with the check button is set to a particular value (normally 1). If the check button is not selected, then the selector is drawn in a different fashion and the associated variable is set to a different value (typically 0). By default, the name of the variable associated with a check button is the same as the name used to create the check button. 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. By default a check button is configured to select and deselect itself on alternate button clicks. In addition, each check button monitors its associated variable and automatically selects and deselects itself when the variables value changes to and from the button’s “on” value.

#### A Checkbutton Widget’s Arguments

The checkbutton 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 ...?

Option and the args determine the exact behavior of the command. The following commands are possible for check button widgets:

pathName :activate

  Change the check button’s state to active and redisplay the button using its active foreground and background colors instead of normal colors. This command is ignored if the check button’s state is disabled. This command is obsolete and will eventually be removed; use “pathName :configure :state active” instead.

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 checkbutton command.

pathName :deactivate

  Change the check button’s state to normal and redisplay the button using its normal foreground and background colors. This command is ignored if the check button’s state is disabled. This command is obsolete and will eventually be removed; use “pathName :configure :state normal” instead.

pathName :deselect

  Deselect the check button: redisplay it without a highlight in the selector and set the associated variable to its “off” value.

pathName :flash

  Flash the check button. This is accomplished by redisplaying the check button several times, alternating between active and normal colors. At the end of the flash the check button is left in the same normal/active state as when the command was invoked. This command is ignored if the check button’s state is disabled.

pathName :invoke

  Does just what would have happened if the user invoked the check button with the mouse: toggle the selection state of the button and invoke the Tcl command associated with the check button, if there is one. The return value is the return value from the Tcl command, or an empty string if there is no command associated with the check button. This command is ignored if the check button’s state is disabled.

pathName :select

  Select the check button: display it with a highlighted selector and set the associated variable to its “on” value.

pathName :toggle

  Toggle 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 check buttons that give them the following default behavior:

- [1] The check button activates whenever the mouse passes over it and deactivates whenever the mouse leaves the check button.
- [2] The check button’s relief is changed to sunken whenever mouse button 1 is pressed over it, and the relief is restored to its original value when button 1 is later released.
- [3] If mouse button 1 is pressed over the check button and later released over the check button, the check button is invoked (i.e. its selection state toggles and the command associated with the button is invoked, if there is one). However, if the mouse is not over the check button when button 1 is released, then no invocation occurs.

If the check button’s state is disabled then none of the above actions occur: the check button is completely non-responsive.

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

#### Keywords

check button, widget

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