Section: User Contributed Perl Documentation (3)
Tk::option - Using the option database in Perl/Tk
The option database (also known as the resource database
application defaults database
) is a set of rules for applying
default options to widgets. Users and system administrators can
set up these rules to customize the appearance of applications
without changing any application code; for example, a user might
set up personal foreground and background colors, or a site
might use fonts associated with visual or language preferences.
Different window managers (and implementations of them) have implemented
the database differently, but most Xt-based window managers use the
file or the xrdb
utility to manage user preferences;
some use both, and/or implement a more complex set of site, user and
application databases. Check your site documentation for these topics
or your window manager's RESOURCE_MANAGER
Being a good citizen
For most applications, the option database ``just works.'' The option...
methods are for applications that need to do something unusual, such as
add new rules or test an option's default. Even in such cases, the
application should provide for user preferences.
Do not hardcode widget options without a very
All users have their own tastes and they are all different.
They choose a special font in a special size and have often spend a
lot of time working out a color scheme that they will love until death.
When you respect their choices they will enjoy working with your
applications much more. Don't destroy the common look and feel of a
Option rules and widget identification
All widgets in an application are identified hierarchically by pathname
starting from the MainWindow
and passing through each widget used to create
the endpoint. The path elements are widget names
, much like the elements
of a file path from the root directory to a file. The rules in the option
database are patterns that are matched against a widget's pathname
determine which defaults apply.
When a widget is created, the Name
option can be
used to assign the widget's name and thus create a distinctive path
for widgets in an application. If the Name
option isn't given,
Perl/Tk assigns a default name based on the type of widget; a
's default name is the appname
. These defaults are fine
for most widgets, so don't feel you need to find a meaningful name for
every widget you create.
A widget must have a distinctive name to allow users to tailor its
options independently of other widgets in an application. For instance,
to create a Text
widget that will
have special options assigned to it, give it a name such as:
$text = $mw->Text(Name => 'importantText');
You can then tailor the widget's attributes with a rule in the option
database such as:
The class attribute identifies groups of widgets, usually within an
application but also to group similar widgets among different applications.
One typically assigns a class to a TopLevel or Frame so that the
class will apply to all of that widget's children. To extend the example,
we could be more specific about the importantText widget
by giving its frame a class:
$frame = $mw->Frame(-class => 'Urgent');
$text = $frame->Text(Name => 'importantText');
Then the resource pattern can be specified as so:
Similarly, the pattern "*Urgent*background: cyan" would apply to all
widgets in the frame.
- $widget->widgetClass(Name=>name, -class=>class);
Identify a new widget with name and/or class.
Name specifies the path element for the widget; names generally begin with a
lowercase letter. -class specifies the class for the widget and its
children; classes generally begin with an uppercase letter.
If not specified, Perl/Tk will assign a unique default name to each widget.
Only MainWindow widgets have a default class, made by uppercasing the
first letter of the application name.
The PathName method returns the widget's pathname, which uniquely
identifies the widget within the application.
- $widget->optionAdd(pattern=>value ?, priority?);
The optionAdd method adds a new option to the database.
Pattern contains the option being specified, and consists of
names and/or classes separated by asterisks or dots, in the usual
X format. Value contains a text string to associate with
pattern; this is the value that will be returned in calls to
the optionGet method. If priority is specified, it indicates
the priority level for this option (see below for legal values);
it defaults to interactive. This method always returns an empty
The optionClear method clears the option database. Default
options (from the RESOURCE_MANAGER property or the .Xdefaults
file) will be reloaded automatically the next time an option is
added to the database or removed from it. This method always returns
an empty string.
The optionGet method returns the value of the option specified for
$widget under name and class. To look up the option,
optionGet matches the patterns in the resource database against
$widget's pathname along with the class of $widget
(or its parent if $widget has no class specified). The widget's
class and name are options set when the widget is created (not
related to class in the sense of bless); the MainWindow's name
is the appname and its class is (by default) derived from the name
of the script.
If several entries in the option database match $widget's pathname,
name, and class, then the method returns whichever was created with
highest priority level. If there are several matching
entries at the same priority level, then it returns whichever entry
was most recently entered into the option database. If there are
no matching entries, then the empty string is returned.
The optionReadfile method reads fileName, which should have the
standard format for an X resource database such as .Xdefaults, and
adds all the options specified in that file to the option database.
If priority is specified, it indicates the priority level at which
to enter the options; priority defaults to interactive.
The priority arguments to the option methods are
normally specified symbolically using one of the following values:
Level 20. Used for default values hard-coded into widgets.
Level 40. Used for options specified in application-specific
Level 60. Used for options specified in user-specific defaults
files, such as .Xdefaults, resource databases loaded into
the X server, or user-specific startup files.
Level 80. Used for options specified interactively after the application
starts running. If priority isn't specified, it defaults to
Any of the above keywords may be abbreviated. In addition, priorities
may be specified numerically using integers between 0 and 100,
inclusive. The numeric form is probably a bad idea except for new priority
levels other than the ones given above.
The priority scheme used by core Tk is not the same as used by normal Xlib
routines. In particular is assumes that the order of the entries is defined,
but user commands like xrdb -merge
can change the order.
database, option, priority, retrieve