button manual page - Tk Built-In Commands

Command-Line Name: -command
Database Name: command
Database 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.
Command-Line Name: -default
Database Name: default
Database Class: Default: Specifies one of three states for the default ring: normal, active, or disabled. In active state, the button is drawn with the platform specific appearance for a default button. In normal state, the button is drawn with the platform specific appearance for a non-default button, leaving enough space to draw the default button appearance. The normal and active states will result in buttons of the same size. In disabled state, the button is drawn with the non-default button appearance without leaving space for the default appearance. The disabled state may result in a smaller button than the active state.
Command-Line Name: -height
Database Name: height
Database Class: 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 is not specified, the button's desired height is computed from the size of the image or bitmap or text being displayed in it.
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.
Command-Line Name: -state
Database Name: state
Database 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 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 button is displayed.
Command-Line Name: -width
Database Name: width
Database Class: 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 a text button (no image or with -compound none) then the width specifies how much space in characters to allocate for the text label. If the width is negative then this specifies a minimum width. If this option is not specified, the button's desired width is computed from the size of the image or bitmap or text being displayed in it.

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, bitmap or image. 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. 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.

WIDGET COMMAND

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 cget option: Returns the current value of the configuration option given by option. Option may have any of the values accepted by the button 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 button command.
pathName flash: Flash the button. This is accomplished by redisplaying the button several times, alternating between the configured activebackground and background 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 default behavior:

A button activates whenever the mouse passes over it and deactivates whenever the mouse leaves the button. Under Windows, this binding is only active when mouse button 1 has been pressed over the button.
A 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.
If mouse button 1 is pressed over a 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.
When a button has the input focus, the space key causes the button to be invoked.

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.

PLATFORM NOTES

On Aqua/Mac OS X, some configuration options are ignored for the purpose of drawing of the widget because they would otherwise conflict with platform guidelines. The configure and cget subcommands can still manipulate the values, but do not cause any variation to the look of the widget. The options affected notably include -background and -relief.

EXAMPLES

This is the classic Tk “Hello, World!” demonstration:

button .b -text "Hello, World!" -command exit
pack .b

This example demonstrates how to handle button accelerators:

button .b1 -text Hello -underline 0
button .b2 -text World -underline 0
bind . <Key-h> {.b1 flash; .b1 invoke}
bind . <Key-w> {.b2 flash; .b2 invoke}
pack .b1 .b2

KEYWORDS

button, widget