button (GCL TK Manual)

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### 2.1 button

button \- Create and manipulate button widgets

#### Synopsis

button 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 Button

`: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.

`: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.

`:state`

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

  Specifies one of three states for the button: normal, active, or disabled. In normal state the button is displayed using the foreground and background options. The active state is typically used when the pointer is over the button. In active state the button is displayed using the activeForeground and activeBackground options. Disabled state means that the 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 button is displayed.

`: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 button command creates a new window (given by the pathName argument) and makes it into a button widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the button such as its colors, font, text, and initial relief. The button 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 button is a widget that displays a textual string or bitmap. 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; and it can be made to flash. When a user invokes the button (by pressing mouse button 1 with the cursor over the button), then the Tcl command specified in the :command option is invoked.

#### A Button Widget’s Arguments

The button 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 button widgets:

pathName :activate

  Change the 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 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 button command.

pathName :deactivate

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 This command is obsolete and will eventually be removed; use “pathName :configure :state normal” instead.

pathName :flash

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

pathName :invoke

  Invoke the Tcl command associated with the 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 button. This command is ignored if the button’s state is disabled.

#### "Default Bindings"

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

- [1] The button activates whenever the mouse passes over it and deactivates whenever the mouse leaves the button.
- [2] The button’s relief is changed to sunken whenever mouse button 1 is pressed over the button, and the relief is restored to its original value when button 1 is later released.
- [3] If mouse button 1 is pressed over the button and later released over the button, the button is invoked. However, if the mouse is not over the button when button 1 is released, then no invocation occurs.

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

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

#### Keywords

button, widget

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