option(3) User Contributed Perl Documentation option(3)NAMEoption - Using the option database in Perl/Tk
SYNOPSISDESCRIPTION
The option database (also known as the resource database or the
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 .Xdefaults 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 property.
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 good reason. 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 personal desktop.
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 to 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 MainWindow'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:
*importantText*foreground: red
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:
*Urgent*importantText*foreground: red
Similarly, the pattern "*Urgent*background: cyan" would apply to all
widgets in the frame.
METHODS
$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.
$widget->PathName;
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 string.
$widget->optionClear;
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.
$widget->optionGet(name,class);
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.
$widget->optionReadfile(fileName?,priority?);
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:
widgetDefault
Level 20. Used for default values hard-coded into widgets.
startupFile
Level 40. Used for options specified in application-
specific startup files.
userDefault
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.
interactive
Level 80. Used for options specified interactively after
the application starts running. If priority isn't
specified, it defaults to this level.
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.
BUGS
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.
SEE ALSO
Tk::Xrm
KEYWORDS
database, option, priority, retrieve
POD ERRORS
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perl v5.10.0 2007-05-05 option(3)
