button Class

Summary

A class of pane that displays either a piece of text or an image, and that performs an action when pressed. Certain types of buttons can also be selected and deselected.

Package

capi

Superclasses

simple-pane
item

Subclasses

push-button
radio-button
check-button

Initargs

Accessors

button-selected
button-image
button-armed-image
button-selected-image
button-disabled-image
button-selected-disabled-image
button-enabled
button-cancel-p
button-default-p

Description

The class button is the class that push-button, radio-button, and check-button are built on. It can be displayed either with text or an image, and a callback is called when the button is clicked. It inherits all of its textual behavior from item, including the slot text which is the text that appears in the button.

Rather than creating direct instances of button, you usually create instances of its subclasses, each of which has a specific interaction style. Occasionally it may be easier to instantiate button directly with the appropriate value of interaction (for instance, when the interaction style is only known at run-time) but you may not use such a button as an item in a button-panel.

The values allowed for interaction are as follows:

Both radio buttons and check buttons can have a selection which can be set using the initarg :selected and the accessor button-selected.

The button's callback gets called when the user clicks on the button, and by default gets passed the data in the button and the interface. This can be changed by specifying a callback type as described in the description of callbacks. The following callbacks are accepted by buttons:

By default, image and disabled-image are nil, meaning that the button is a text button, but if image is provided then the button displays an image instead of the text. The image can be an external-image or any object accepted by load-image, including a .ico file on Microsoft Windows. The disabled image is the image that is shown when the button is disabled (or nil, meaning that it is left for the window system to decide how to display the image as disabled). On some platforms the system computes the disabled image and so disabled-image is ignored.

The button's actions can be enabled and disabled with the enabled slot, and its associated accessor button-enabled. This means that when the button is disabled, pressing on it does not call any callbacks or change its selection.

Note that the class button-panel provides functionality to group buttons together, and should normally be used in preference to creating individual buttons yourself. For instance, a radio-button-panel makes a number of radio buttons and also controls them such that only one button is ever selected at a time.

A mnemonic is an underlined character within the button text or the printed representation of the button data which can be entered to select the button. The value mnemonic is interpreted as described for menu.

An alternative way to specify a mnemonic is to pass mnemonic-text. This is a string which provides the text for the button and also specifies the mnemonic character. mnemonic-text and mnemonic-escape are interpreted in just the same way as the mnemonic-title and mnemonic-escape of menu.

Notes

1. The simple-pane initarg foreground is not supported for buttons on Windows and Cocoa.
2. The disabled-image, armed-image and selected-disabled-image will work on Microsoft Windows provided you are running with the themed look-and-feel (which is the default). See 19.1.1 Using Windows themes.

Examples

In the following example a button is created. Using the button-enabled accessor the button is then enabled and disabled.

(setq button
      (capi:contain (make-instance 
                     'capi:push-button
                     :text "Press Me")))
 
(capi:apply-in-pane-process
 button #'(setf capi:button-enabled) nil button)
 
(capi:apply-in-pane-process
 button #'(setf capi:button-enabled) t button)

In the next example a button with an image instead of text is created.

(setq button
      (capi:contain 
       (make-instance
        'capi:push-button
        :image 
        (example-file
         "capi/applications/images/info.bmp"))))

The following examples illustrate mnemonics:

(defun egg (&rest ignore) 
  (declare (ignore ignore))
  (capi:display-message "Egg"))
 
(capi:contain 
 (make-instance 'capi:push-button  
                :selection-callback 'egg
                :mnemonic-text "Chicken && Rice"))
 
(capi:contain 
 (make-instance 'capi:push-button  
                :data "Chicken"
                :selection-callback 'egg
                :mnemonic #\k))

Compare this with the previous example: the #\k does not appear and the #\e becomes the mnemonic:

(capi:contain 
 (make-instance 'capi:push-button  
                :selection-callback 'egg
                :mnemonic-escape  #\k      
                :mnemonic-text "Chicken"))

Also see these examples:

(example-edit-file "capi/buttons/")

See also

button-panel
callbacks
3.10 Button elements
13.10 Working with images