widget: Introduction
1 Introduction
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Most graphical user interface toolkits provide a number of standard user
interface controls (sometimes known as “widgets” or “gadgets”). Emacs
doesn’t really support anything like this, except for an incredibly
powerful text “widget.” On the other hand, Emacs does provide the
necessary primitives to implement many other widgets within a text
buffer. The ‘widget’ package simplifies this task.
The basic widgets are:
‘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:
1. More complex fields than just editable text are supported.
2. You can give the users immediate feedback if they enter invalid
data in a text field, and sometimes prevent entering invalid data.
3. You can have fixed sized fields, thus allowing multiple fields to
be lined up in columns.
4. It is simple to query or set the value of a field.
5. Editing happens in the buffer, not in the mini-buffer.
6. Packages using the library get a uniform look, making them easier
for the user to learn.
7. As support for embedded graphics improve, the widget library will
be extended to use the GUI features. This means that your code
using the widget library will also use the new graphic features
automatically.
Info Catalog
widget: Top
widget: Top
widget: User Interface