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Most graphical user interface toolkits provide
a number of standard user interface controls (sometimes known as
‘widgets’ or ‘gadgets’). Historically, Emacs didn’t support anything like
this, except for its incredible powerful text “widget”. However,
since XEmacs 21.4, XEmacs has supported “native” widgets (GUI controls
implemented as Lisp APIs in C for the MS Windows, Motif, Athena, and GTK
toolkits) and libglade (GUI controls with an XML API for the GTK
toolkit). On the other hand, Emacs does provide the necessary
primitives to implement many other widgets within a text buffer, and of
course this is the only way to implement self-contained controls in a
text terminal. The widget
package simplifies this task.
Examples of some basic widgets include:
link
Areas of text with an associated action. Intended for hypertext links embedded in text.
push-button
Like link, but intended for stand-alone buttons.
editable-field
An editable text field. It can be either variable or fixed length.
menu-choice
Allows the user to choose one of multiple options from a menu, each option is itself a widget. Only the selected option will be visible in the buffer.
radio-button-choice
Allows the user to choose one of multiple options by activating radio buttons. The options are implemented as widgets. All options will be visible in the buffer.
item
A simple constant widget intended to be used in the menu-choice
and
radio-button-choice
widgets.
choice-item
A button item only intended for use in choices. When invoked, the user will be asked to select another option from the choice widget.
toggle
A simple ‘on’/‘off’ switch.
checkbox
A checkbox (‘[ ]’/‘[X]’).
editable-list
Create an editable list. The user can insert or delete items in the list. Each list item is itself a widget.
Now, of what possible use can support for widgets be in a text editor? I’m glad you asked. The answer is that widgets are useful for implementing forms. A form in Emacs is a buffer where the user is supposed to fill out a number of fields, each of which has a specific meaning. The user is not supposed to change or delete any of the text between the fields. Examples of forms in Emacs are the ‘forms’ package (of course), the customize buffers, the mail and news compose modes, and the HTML form support in the ‘w3’ browser.
The advantages for a programmer of using the widget
package to
implement forms are:
In order to minimize the code that is loaded by users who does not create any widgets, the code has been split in two files:
This declares the user variables, defines the function
define-widget
, and autoloads the function widget-create
.
Everything else is here. Do not load it explicitly, as it will be autoloaded when needed.
In order to minimize the code that is loaded by users who does not create any widgets, the code has been split in two files:
This will declare the user variables, define the function
widget-define
, and autoload the function widget-create
.
Everything else is here, there is no reason to load it explicitly, as it will be autoloaded when needed.
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A form consists of read only text for documentation and some fields, where each field contains two parts, a tag and a value. The tags are used to identify the fields, so the documentation can refer to the ‘foo field’, meaning the field tagged with ‘Foo’. Here is an example form:
Here is some documentation. Name: My Name Choose: This option Address: Some Place In some City Some country. See also _other work_ for more information. Numbers: count to three below [INS] [DEL] One [INS] [DEL] Eh, two? [INS] [DEL] Five! [INS] Select multiple: [X] This [ ] That [X] Thus Select one: (*) One ( ) Another One. ( ) A Final One. [Apply Form] [Reset Form] |
The top level widgets in this example are tagged ‘Name’, ‘Choose’, ‘Address’, ‘_other work_’, ‘Numbers’, ‘Select multiple’, ‘Select one’, ‘[Apply Form]’, and ‘[Reset Form]’. There are basically two things the user can do within a form, namely editing the editable text fields and activating the buttons.
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In the example, the value for the ‘Name’ is most likely displayed in an editable text field, and so are values for each of the members of the ‘Numbers’ list. All the normal Emacs editing operations are available for editing these fields. The only restriction is that each change you make must be contained within a single editable text field. For example, capitalizing all text from the middle of one field to the middle of another field is prohibited.
Editable text fields are created by the editable-field
widget.
Warning: In an editable-field
widget, the editable
field must not be adjacent to another widget—that won’t work.
You must put some text in between. Either make this text part of
the editable-field
widget itself, or insert it with
widget-insert
.
The :format
keyword is useful for generating the necessary
text; for instance, if you give it a value of "Name: %v "
,
the ‘Name: ’ part will provide the necessary separating text
before the field and the trailing space will provide the
separating text after the field. If you don’t include the
:size
keyword, the field will extend to the end of the
line, and the terminating newline will provide separation after.
Warning: In an editable-field
widget, the ‘%v’ escape
must be preceded by some other text in the :format
string
(if specified).
The editing text fields are highlighted with the
widget-field-face
face, making them easy to find.
Face used for other editing fields.
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Some portions of the buffer have an associated action, which can be invoked by a standard key or mouse command. These portions are called buttons. The default commands for activating a button are:
Invoke the button at pos, defaulting to point.
If point is not located on a button, invoke the binding in
widget-global-map
(by default the global map).
Invoke the button at the location of the mouse pointer. If the mouse
pointer is located in an editable text field, invoke the binding in
widget-global-map
(by default the global map).
There are several different kind of buttons, all of which are present in the example:
When you invoke one of these buttons, you will be asked to choose
between a number of different options. This is how you edit an option
field. Option fields are created by the menu-choice
widget. In
the example, ‘Choose’ is an option field tag.
Activating these will insert or delete elements from an editable list.
The list is created by the editable-list
widget.
The ‘_other work_’ is an example of an embedded
button. Embedded buttons are not associated with any fields, but can serve
any purpose, such as implementing hypertext references. They are
usually created by the link
widget.
Activating one of these will convert it to the other. This is useful
for implementing multiple-choice fields. You can create them with the
checkbox
widget.
Only one radio button in a radio-button-choice
widget can be
selected at any time. When you invoke one of the unselected radio
buttons, it will be selected and the previous selected radio button will
become unselected.
These are explicit buttons made with the push-button
widget. The
main difference from the link
widget is that the buttons will be
displayed as GUI buttons when possible.
To make them easier to locate, buttons are emphasized in the buffer.
Face used for buttons.
Face used for highlighting a button when the mouse pointer moves across it.
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You can use all the normal Emacs commands to move around in a form buffer, plus you will have these additional commands:
Move point count buttons or editing fields forward.
Move point count buttons or editing fields backward.
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Here is the code to implement the user interface example (see section User Interface).
(require 'widget) (eval-when-compile (require 'wid-edit)) (defvar widget-example-repeat) (defun widget-example () "Create the widgets from the Widget manual." (interactive) (kill-buffer (get-buffer-create "*Widget Example*")) (switch-to-buffer (get-buffer-create "*Widget Example*")) (kill-all-local-variables) (make-local-variable 'widget-example-repeat) (widget-insert "Here is some documentation.\n\n") (widget-create 'editable-field :size 13 :format "Name: %v " ; Text after the field! "My Name") (widget-create 'menu-choice :tag "Choose" :value "This" :help-echo "Choose me, please!" :notify (lambda (widget &rest ignore) (message "%s is a good choice!" (widget-value widget))) '(item :tag "This option" :value "This") '(choice-item "That option") '(editable-field :menu-tag "No option" "Thus option")) (widget-create 'editable-field :format "Address: %v" "Some Place\nIn some City\nSome country.") (widget-insert "\nSee also ") (widget-create 'link :notify (lambda (&rest ignore) (widget-value-set widget-example-repeat '("En" "To" "Tre")) (widget-setup)) "other work") (widget-insert " for more information.\n\nNumbers: count to three below\n") (setq widget-example-repeat (widget-create 'editable-list :entry-format "%i %d %v" :notify (lambda (widget &rest ignore) (let ((old (widget-get widget ':example-length)) (new (length (widget-value widget)))) (unless (eq old new) (widget-put widget ':example-length new) (message "You can count to %d." new)))) :value '("One" "Eh, two?" "Five!") '(editable-field :value "three"))) (widget-insert "\n\nSelect multiple:\n\n") (widget-create 'checkbox t) (widget-insert " This\n") (widget-create 'checkbox nil) (widget-insert " That\n") (widget-create 'checkbox :notify (lambda (&rest ignore) (message "Tickle")) t) (widget-insert " Thus\n\nSelect one:\n\n") (widget-create 'radio-button-choice :value "One" :notify (lambda (widget &rest ignore) (message "You selected %s" (widget-value widget))) '(item "One") '(item "Another One.") '(item "A Final One.")) (widget-insert "\n") (widget-create 'push-button :notify (lambda (&rest ignore) (if (= (length (widget-value widget-example-repeat)) 3) (message "Congratulation!") (error "Three was the count!"))) "Apply Form") (widget-insert " ") (widget-create 'push-button :notify (lambda (&rest ignore) (widget-example)) "Reset Form") (widget-insert "\n") (use-local-map widget-keymap) (widget-setup)) |
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Widgets are created with widget-create
, which returns a
widget object. This object can be queried and manipulated by
other widget functions, until it is deleted with widget-delete
.
After the widgets have been created, widget-setup
must be called
to enable them.
Create and return a widget of type type. The syntax for the type argument is described in Basic Types.
The keyword arguments can be used to overwrite the keyword arguments that are part of type.
Delete widget and remove it from the buffer.
Set up a buffer to support widgets.
This should be called after creating all the widgets and before allowing the user to edit them.
If you want to insert text outside the widgets in the form, the
recommended way to do that is with widget-insert
.
Insert the arguments, either strings or characters, at point. The inserted text will be read-only.
There is a standard widget keymap which you might find useful.
A keymap with the global keymap as its parent.
<TAB> and C-<TAB> are bound to widget-forward
and
widget-backward
, respectively. <RET> and Mouse-2
are bound to widget-button-press
and
widget-button-click
.
Keymap used by widget-button-press
and widget-button-click
when not on a button. By default this is global-map
.
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This is the general syntax of a type specification:
name ::= (name [keyword argument]... args) | name |
where name is a widget name, keyword is the name of a property, argument is the value of the property, and args are interpreted in a widget specific way.
The following keyword arguments apply to all widgets:
:value
The initial value for widgets of this type.
:format
This string will be inserted in the buffer when you create a widget. The following ‘%’ escapes are available:
The text inside will be marked as a button.
By default, the text will be shown in widget-button-face
, and
surrounded by brackets.
String to prefix buttons.
String to suffix buttons.
The text inside will be displayed in the face specified by
:sample-face
.
This will be replaced with the buffer representation of the widget’s value. What this is depends on the widget type.
Warning: In an editable-field
widget, the ‘%v’ escape
must be preceded by some other text in the format string (if specified).
Insert the string specified by :doc
here.
Like ‘%d’, with the following modifications: If the documentation
string is more than one line, it will add a button which will toggle
between showing only the first line, and showing the full text.
Furthermore, if there is no :doc
property in the widget, it will
instead examine the :documentation-property
property. If it is a
lambda expression, it will be called with the widget’s value as an
argument, and the result will be used as the documentation text.
Insert the string specified by :tag
here, or the princ
representation of the value if there is no tag.
Insert a literal ‘%’.
:button-face
Face used to highlight text inside %[ %] in the format.
:button-prefix
:button-suffix
Text around %[ %] in the format.
These can be
No text is inserted.
The string is inserted literally.
The value of the symbol is expanded according to this table.
:doc
The string inserted by the ‘%d’ or ‘%h’ escape in the format string.
:tag
The string inserted by the ‘%t’ escape in the format string.
:tag-glyph
Name of image to use instead of the string specified by :tag
on
Emacsen that supports it.
:help-echo
Specifies how to display a message whenever you move to the widget with
either widget-forward
or widget-backward
or move the mouse
over it (using the standard help-echo
mechanism). The argument
is either a string to display, a function of one argument, the widget,
which should return a string to display, or a form that evaluates to
such a string.
:follow-link
Specifies how to interpret a <mouse-1> click on the widget. See (elisp)Clickable Text section ‘Defining Clickable Text’ in the Emacs Lisp Reference Manual.
:indent
An integer indicating the absolute number of spaces to indent children of this widget.
:offset
An integer indicating how many extra spaces to add to the widget’s grandchildren compared to this widget.
:extra-offset
An integer indicating how many extra spaces to add to the widget’s children compared to this widget.
:notify
A function called each time the widget or a nested widget is changed.
The function is called with two or three arguments. The first argument
is the widget itself, the second argument is the widget that was
changed, and the third argument is the event leading to the change, if
any. In editable fields, this includes all insertions, deletions,
etc. To watch only for “final” actions, redefine the
:action
callback.
:menu-tag
Tag used in the menu when the widget is used as an option in a
menu-choice
widget.
:menu-tag-get
Function used for finding the tag when the widget is used as an option
in a menu-choice
widget. By default, the tag used will be either the
:menu-tag
or :tag
property if present, or the princ
representation of the :value
property if not.
:match
Should be a function called with two arguments, the widget and a value,
and returning non-nil
if the widget can represent the specified value.
:validate
A function which takes a widget as an argument, and returns nil
if the widget’s current value is valid for the widget. Otherwise it
should return the widget containing the invalid data, and set that
widget’s :error
property to a string explaining the error.
The following predefined function can be used:
All the :children
of widget must be valid.
:tab-order
Specify the order in which widgets are traversed with
widget-forward
or widget-backward
. This is only partially
implemented.
-1
are ignored.
nil
,
whichever comes first.
nil
:parent
The parent of a nested widget (e.g. a menu-choice
item or an
element of an editable-list
widget).
:sibling-args
This keyword is only used for members of a radio-button-choice
or
checklist
. The value should be a list of extra keyword
arguments, which will be used when creating the radio-button
or
checkbox
associated with this item.
Directory where glyphs are found. Widget will look here for a file with the same name as specified for the image, with either a ‘.xpm’ (if supported) or ‘.xbm’ extension.
If non-nil
, allow glyphs to appear on displays where they are supported.
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link
WidgetSyntax:
type ::= (link [keyword argument]... [ value ]) |
The value, if present, is used to initialize the :value
property. The value should be a string, which will be inserted in the
buffer.
By default the link will be shown in brackets.
String to prefix links.
String to suffix links.
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url-link
WidgetSyntax:
type ::= (url-link [keyword argument]... url) |
When this link is invoked, the WWW browser specified by
browse-url-browser-function
will be called with url.
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info-link
WidgetSyntax:
type ::= (info-link [keyword argument]... address) |
When this link is invoked, the built-in Info reader is started on address.
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push-button
WidgetSyntax:
type ::= (push-button [keyword argument]... [ value ]) |
The value, if present, is used to initialize the :value
property. The value should be a string, which will be inserted in the
buffer.
By default the tag will be shown in brackets.
String to prefix push buttons.
String to suffix push buttons.
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editable-field
WidgetSyntax:
type ::= (editable-field [keyword argument]... [ value ]) |
The value, if present, is used to initialize the :value
property. The value should be a string, which will be inserted in the
field. This widget will match all string values.
The following extra properties are recognized:
:size
The minimum width of the editable field.
By default the field will reach to the end of the line. If the
content is too large, the displayed representation will expand to
contain it. The content is not truncated to size.
:value-face
Face used for highlighting the editable field. Default is
widget-field-face
, see User Interface.
:secret
Character used to display the value. You can set this to e.g. ?*
if the field contains a password or other secret information. By
default, this is nil
, and the value is not secret.
:valid-regexp
By default the :validate
function will match the content of the
field with the value of this attribute. The default value is ""
which matches everything.
:keymap
Keymap used in the editable field. The default value is
widget-field-keymap
, which allows you to use all the normal
editing commands, even if the buffer’s major mode suppresses some of
them. Pressing <RET> invokes the function specified by
:action
.
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text
WidgetThis is just like editable-field
, but intended for multiline text
fields. The default :keymap
is widget-text-keymap
, which
does not rebind the <RET> key.
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menu-choice
WidgetSyntax:
type ::= (menu-choice [keyword argument]... type ... ) |
The type argument represents each possible choice. The widget’s value will be that of the chosen type argument. This widget will match any value matching at least one of the specified type arguments.
:void
Widget type used as a fallback when the value does not match any of the specified type arguments.
:case-fold
Set this to nil
if you don’t want to ignore case when prompting for a
choice through the minibuffer.
:children
A list whose CAR is the widget representing the currently chosen type in the buffer.
:choice
The current chosen type.
:args
The list of types.
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radio-button-choice
WidgetSyntax:
type ::= (radio-button-choice [keyword argument]... type ... ) |
The component types specify the choices, with one radio button for each. The widget’s value will be that of the chosen type argument. This widget matches any value that matches at least one of the specified type arguments.
The following extra properties are recognized.
:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
Replace with the buffer representation of the type widget.
Replace with the radio button.
Insert a literal ‘%’.
:button-args
A list of keywords to pass to the radio buttons. Useful for setting e.g. the ‘:help-echo’ for each button.
:buttons
The widgets representing the radio buttons.
:children
The widgets representing each type.
:choice
The current chosen type
:args
The list of types.
You can add extra radio button items to a radio-button-choice
widget after it has been created with the function
widget-radio-add-item
.
Add to radio-button-choice
widget widget a new radio button
item of type type.
Please note that such items added after the radio-button-choice
widget has been created will not be properly destructed when
you call widget-delete
.
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item
WidgetSyntax:
item ::= (item [keyword argument]... value) |
The value, if present, is used to initialize the :value
property. The value should be a string, which will be inserted in the
buffer. This widget will only match the specified value.
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choice-item
WidgetSyntax:
item ::= (choice-item [keyword argument]... value) |
The value, if present, is used to initialize the :value
property. The value should be a string, which will be inserted in the
buffer as a button. Activating the button of a choice-item
is
equivalent to activating the parent widget. This widget will only match
the specified value.
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toggle
WidgetSyntax:
type ::= (toggle [keyword argument]...) |
The widget has two possible states, ‘on’ and ‘off’, which
correspond to a t
or nil
value, respectively.
The following extra properties are recognized:
:on
A string representing the ‘on’ state. By default the string ‘on’.
:off
A string representing the ‘off’ state. By default the string ‘off’.
:on-glyph
Name of a glyph to be used instead of the ‘:on’ text string, on emacsen that supports this.
:off-glyph
Name of a glyph to be used instead of the ‘:off’ text string, on emacsen that supports this.
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checkbox
WidgetThis widget has two possible states, ‘selected’ and
‘unselected’, which corresponds to a t
or nil
value.
Syntax:
type ::= (checkbox [keyword argument]...) |
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checklist
WidgetSyntax:
type ::= (checklist [keyword argument]... type ... ) |
The type arguments represent each checklist item. The widget’s value will be a list containing the values of all checked type arguments. The checklist widget will match a list whose elements all match at least one of the specified type arguments.
The following extra properties are recognized:
:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
Replaced with the buffer representation of the type widget.
Replace with the checkbox.
Insert a literal ‘%’.
:greedy
Usually a checklist will only match if the items are in the exact
sequence given in the specification. By setting :greedy
to
non-nil
, it will allow the items to appear in any sequence.
However, if you extract the value they will be in the sequence given
in the checklist, i.e. the original sequence is forgotten.
:button-args
A list of keywords to pass to the checkboxes. Useful for setting e.g. the ‘:help-echo’ for each checkbox.
:buttons
The widgets representing the checkboxes.
:children
The widgets representing each type.
:args
The list of types.
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editable-list
WidgetSyntax:
type ::= (editable-list [keyword argument]... type) |
The value is a list, where each member represents one widget of type type.
The following extra properties are recognized:
:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
This will be replaced with the buffer representation of the type widget.
Insert the [INS] button.
Insert the [DEL] button.
Insert a literal ‘%’.
:insert-button-args
A list of keyword arguments to pass to the insert buttons.
:delete-button-args
A list of keyword arguments to pass to the delete buttons.
:append-button-args
A list of keyword arguments to pass to the trailing insert button.
:buttons
The widgets representing the insert and delete buttons.
:children
The widgets representing the elements of the list.
:args
List whose CAR is the type of the list elements.
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group
WidgetThis widget simply groups other widgets together.
Syntax:
type ::= (group [keyword argument]... type...) |
The value is a list, with one member for each type.
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A number of widgets for editing s-expressions (Lisp types), sexp for short, are also available. These basically fall in several categories described in this section.
0.6.1 The Constant Widgets | ||
0.6.2 Generic Sexp Widget | ||
0.6.3 Atomic Sexp Widgets | ||
0.6.4 Composite Sexp Widgets |
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The const
widget can contain any Lisp expression, but the user is
prohibited from editing it, which is mainly useful as a component of one
of the composite widgets.
The syntax for the const
widget is:
type ::= (const [keyword argument]... [ value ]) |
The value, if present, is used to initialize the :value
property and can be any s-expression.
This will display any valid s-expression in an immutable part of the buffer.
There are two variations of the const
widget, namely
variable-item
and function-item
. These should contain a
symbol with a variable or function binding. The major difference from
the const
widget is that they will allow the user to see the
variable or function documentation for the symbol.
An immutable symbol that is bound as a variable.
An immutable symbol that is bound as a function.
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The sexp
widget can contain any Lisp expression, and allows the
user to edit it inline in the buffer.
The syntax for the sexp
widget is:
type ::= (sexp [keyword argument]... [ value ]) |
This will allow you to edit any valid s-expression in an editable buffer field.
The sexp
widget takes the same keyword arguments as the
editable-field
widget. See section The editable-field
Widget.
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The atoms are s-expressions that do not consist of other s-expressions. For example, a string, a file name, or a symbol are atoms, while a list is a composite type. You can edit the value of an atom with the following widgets.
The syntax for all the atoms are:
type ::= (construct [keyword argument]... [ value ]) |
The value, if present, is used to initialize the :value
property and must be an expression of the same type as the widget.
That is, the string widget can only be initialized with a string.
All the atom widgets take the same keyword arguments as the
editable-field
widget. See section The editable-field
Widget.
Allows you to edit a string in an editable field.
Allows you to edit a regular expression in an editable field.
Allows you to enter a character in an editable field.
Allows you to edit a file name in an editable field.
Keywords:
:must-match
If this is set to non-nil
, only existing file names will be
allowed in the minibuffer.
Allows you to edit a directory name in an editable field.
Similar to the file
widget.
Allows you to edit a Lisp symbol in an editable field.
Allows you to edit a lambda expression, or a function name with completion.
Allows you to edit a variable name, with completion.
Allows you to edit an integer in an editable field.
Allows you to edit a number in an editable field.
Allows you to edit a boolean. In Lisp this means a variable which is
either nil
meaning false, or non-nil
meaning true.
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The syntax for the composite widget construct is:
type ::= (construct [keyword argument]... component...) |
where each component must be a widget type. Each component widget will be displayed in the buffer, and will be editable by the user.
The value of a cons
widget must be a cons-cell whose CAR
and CDR have two specified types. It uses this syntax:
type ::= (cons [keyword argument]... car-type cdr-type) |
The value matched by a choice
widget must have one of a fixed
set of types. The widget’s syntax is as follows:
type ::= (choice [keyword argument]... type ... ) |
The value of a choice
widget can be anything that matches any of the
types.
The value of a list
widget must be a list whose element types
match the specified component types:
type ::= (list [keyword argument]... component-type...) |
Thus, (list string number)
matches lists of two elements,
the first being a string and the second being a number.
The vector
widget is like the list
widget but matches
vectors instead of lists. Thus, (vector string number)
matches
vectors of two elements, the first being a string and the second being
a number.
The above suffice for specifying fixed size lists and vectors. To get
variable length lists and vectors, you can use a choice
,
set
, or repeat
widget together with the :inline
keyword. If any component of a composite widget has the
:inline
keyword set, its value must be a list which will then
be spliced into the composite. For example, to specify a list whose
first element must be a file name, and whose remaining elements should
either be the symbol t
or two strings (file names), you can use
the following widget specification:
(list file (choice (const t) (list :inline t :value ("foo" "bar") string string))) |
The value of a widget of this type will either have the form
(file t)
or (file string string)
.
This concept of :inline
may be hard to understand. It was
certainly hard to implement, so instead of confusing you more by
trying to explain it here, I’ll just suggest you meditate over it for
a while.
Specifies a type whose values are the lists whose elements all belong to a given set. The order of elements of the list is not significant. Here’s the syntax:
type ::= (set [keyword argument]... permitted-element ... ) |
Use const
to specify each permitted element, like this:
(set (const a) (const b))
.
Specifies a list of any number of elements that fit a certain type.
type ::= (repeat [keyword argument]... type) |
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You can examine or set the value of a widget by using the widget object
that was returned by widget-create
.
Return the current value contained in widget. It is an error to call this function on an uninitialized widget.
Set the value contained in widget to value. It is an error to call this function with an invalid value.
Important: You must call widget-setup
after
modifying the value of a widget before the user is allowed to edit the
widget again. It is enough to call widget-setup
once if you
modify multiple widgets. This is currently only necessary if the widget
contains an editing field, but may be necessary for other widgets in the
future.
If your application needs to associate some information with the widget
objects, for example a reference to the item being edited, it can be
done with widget-put
and widget-get
. The property names
must begin with a ‘:’.
In widget set property to value. property should be a symbol, while value can be anything.
In widget return the value for property.
property should be a symbol, the value is what was last set by
widget-put
for property.
Non-nil
if widget has a value (even nil
) for
property property.
Occasionally it can be useful to know which kind of widget you have, i.e. the name of the widget type you gave when the widget was created.
Return the name of widget, a symbol.
Widgets can be in two states: active, which means they are modifiable by the user, or inactive, which means they cannot be modified by the user. You can query or set the state with the following code:
;; Examine if widget is active or not. (if (widget-apply widget :active) (message "Widget is active.") (message "Widget is inactive.") ;; Make widget inactive. (widget-apply widget :deactivate) ;; Make widget active. (widget-apply widget :activate) |
A widget is inactive if it, or any of its ancestors (found by
following the :parent
link), have been deactivated. To make sure
a widget is really active, you must therefore activate both it and
all its ancestors.
(while widget (widget-apply widget :activate) (setq widget (widget-get widget :parent))) |
You can check if a widget has been made inactive by examining the value
of the :inactive
keyword. If this is non-nil
, the widget itself
has been deactivated. This is different from using the :active
keyword, in that the latter tells you if the widget or any of
its ancestors have been deactivated. Do not attempt to set the
:inactive
keyword directly. Use the :activate
:deactivate
keywords instead.
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You can define specialized widgets with define-widget
. It allows
you to create a shorthand for more complex widgets, including specifying
component widgets and new default values for the keyword
arguments.
Define a new widget type named name from class
.
name and class should both be symbols, class
should be one
of the existing widget types.
The third argument doc is a documentation string for the widget.
After the new widget has been defined the following two calls will create identical widgets:
(widget-create name) |
(apply widget-create class args) |
Using define-widget
just stores the definition of the widget type
in the widget-type
property of name, which is what
widget-create
uses.
If you only want to specify defaults for keywords with no complex
conversions, you can use identity
as your :convert-widget
function.
The following additional keyword arguments are useful when defining new widgets:
:convert-widget
Method to convert type-specific components of a widget type before
instantiating a widget of that type. Not normally called from user
code, it is invoked by widget-convert
. Typical operations
include converting types of child widgets to widget instances and
converting values from external format (i.e., as expected by the
calling code) to internal format (which is often different for the
convenience of widget manipulation). It takes a widget type as an
argument, and returns the converted widget type. When a widget is
created, the value of this property is called for the widget type, then
for all the widget’s parent types, most derived first. (The property is
reevaluated for each parent type.)
The following predefined functions can be used here:
Convert each member of :args
in widget from a widget type
to a widget.
Initialize :value
from (car :args)
in widget, and
reset :args
.
:copy
Function to deep copy a widget type. It takes a shallow copy of the
widget type as an argument (made by copy-sequence
), and returns a
deep copy. The purpose of this is to avoid having different instances
of combined widgets share nested attributes. Any member of the
widget which might be changed in place (rather than replaced) should be
copied by this method. (widget-copy
uses copy-sequence
to
ensure that the top-level list is a copy.) This particularly applies to
child widgets.
The following predefined functions can be used here:
Copy :args
as widget types in widget.
:value-to-internal
Function to convert the value to the internal format. The function
takes two arguments, a widget and an external value. It returns the
internal value. The function is called on the present :value
when the widget is created, and on any value set later with
widget-value-set
.
:value-to-external
Function to convert the value to the external format. The function
takes two arguments, a widget and an internal value, and returns the
external value. The function is called on the present :value
when the widget is created, and on any value set later with
widget-value-set
.
:create
Function to create a widget from scratch. The function takes one
argument, a widget, and inserts it in the buffer. Not normally called
from user code. Instead, call widget-create
or related
functions, which take a type argument, (usually) convert it to a widget,
call the :create
function to insert it in the buffer, and then
return the (possibly converted) widget.
The default, widget-default-create
, is invariably appropriate.
(None of the standard widgets specify :create
.)
:delete
Function to delete a widget. The function takes one argument, a widget, and should remove all traces of the widget from the buffer.
The default value is:
Remove widget from the buffer.
Delete all :children
and :buttons
in widget.
In most cases you should not change this value, but instead use
:value-delete
to make any additional cleanup.
:value-create
Function to expand the ‘%v’ escape in the format string. It will be called with the widget as its argument and should insert a representation of the widget’s value in the buffer.
Nested widgets should be listed in :children
or :buttons
to make sure they are automatically deleted.
:value-delete
Should remove the representation of the widget’s value from the buffer.
It will be called with the widget as its argument. It doesn’t have to
remove the text, but it should release markers and delete nested widgets
if these are not listed in :children
or :buttons
.
:value-get
Function to extract the value of a widget, as it is displayed in the buffer.
The following predefined function can be used here:
Return the :value
property of widget.
:format-handler
Function to handle unknown ‘%’ escapes in the format string. It will be called with the widget and the character that follows the ‘%’ as arguments. You can set this to allow your widget to handle non-standard escapes.
You should end up calling widget-default-format-handler
to handle
unknown escape sequences. It will handle the ‘%h’ and any future
escape sequences as well as give an error for unknown escapes.
:action
Function to handle user initiated events. By default, :notify
the parent. Actions normally do not include mere edits, but refer to
things like invoking buttons or hitting enter in an editable field. To
watch for any change, redefine the :notify
callback.
The following predefined function can be used here:
Tell :parent
of widget to handle the :action
.
Optional event is the event that triggered the action.
:prompt-value
Function to prompt for a value in the minibuffer. The function should
take four arguments, widget, prompt, value, and
unbound and should return a value for widget entered by the user.
prompt is the prompt to use. value is the default value to
use, unless unbound is non-nil
, in which case there is no default
value. The function should read the value using the method most natural
for this widget and does not have to check whether it matches.
If you want to define a new widget from scratch, use the default
widget as its base.
Widget used as a base for other widgets.
It provides most of the functionality that is referred to as “by default” in this text.
In implementing complex hierarchical widgets (e.g., using the ‘group’ widget), the following functions may be useful. The syntax for the type arguments to these functions is described in Basic Types.
As a child of parent, create a widget with type type and
value value. type is copied, and the :widget-convert
method is applied to the optional keyword arguments from args.
As a child of parent, create a widget with type type. type is copied, but no conversion method is applied.
As a child of parent, create a widget with type type and value value. type is copied, but no conversion method is applied.
Convert type to a widget without inserting it in the buffer. The optional args are additional keyword arguments.
The widget’s :args
property is set from the longest tail of
args whose ‘cdr’ is not a keyword, or if that is null, from
the longest tail of type’s :args
property whose cdr is not
a keyword. Keyword arguments from args are set, and the
:value
property (if any) is converted from external to internal
format.
widget-convert
is typically not called from user code; rather it
is called implicitly through the ‘widget-create*’ functions.
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There is a separate package to browse widgets. This is intended to help programmers who want to examine the content of a widget. The browser shows the value of each keyword, but uses links for certain keywords such as ‘:parent’, which avoids printing cyclic structures.
Create a widget browser for widget. When called interactively, prompt for widget.
Create a widget browser for widget and show it in another window. When called interactively, prompt for widget.
Create a widget browser for the widget at pos. When called interactively, use the position of point.
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There is a minor mode for manipulating widgets in major modes that don’t provide any support for widgets themselves. This is mostly intended to be useful for programmers doing experiments.
Toggle minor mode for traversing widgets. With arg, turn widget mode on if and only if arg is positive.
Keymap used in widget-minor-mode
.
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Prompt for a value matching widget, using prompt.
The current value is assumed to be value, unless unbound is
non-nil
.
Get the item which widget is assumed to toggle.
This is only meaningful for radio buttons or checkboxes in a list.
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menu-choice
tag should be prettier, something like the abbreviated
menus in Open Look.
:tab-order
.
property-list
widget.
association-list
widget.
key-binding
widget.
widget
widget for editing widget specifications.
TeX-printer-list
for an explanation.
widget-prompt-value
should give type specific help.
mailto
widget.
describe-function
or
widget-browse-other-window
and friends directly, instead of going
through apropos
. If more than one function is valid for the
symbol, it should pop up a menu.
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This (very brief!) section provides a few notes on the internal structure and implementation of Emacs widgets. Avoid relying on this information. (We intend to improve it, but this will take some time.) To the extent that it actually describes APIs, the information will be moved to appropriate sections of the manual in due course.
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Widgets and types are currently both implemented as lists.
A symbol may be defined as a type name using define-widget
.
See section Defining New Widgets. A type is a list whose car is a
previously defined type name, nil, or (recursively) a type. The car is
the class or parent type of the type, and properties which are not
specified in the new type will be inherited from ancestors. Probably
the only type without a class should be the default
type. The
cdr of a type is a plist whose keys are widget property keywords.
A type or type name may also be referred to as an unconverted widget.
A converted widget or widget instance is a list whose car is a type name or a type, and whose cdr is a property list. Furthermore, all children of the converted widget must be converted. Finally, in the process of appropriate parts of the list structure are copied to ensure that changes in values of one instance do not affect another’s.
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