NAME

       Tk::option - Using the option database in Perl/Tk

SYNOPSIS

           $widget->widgetClass(Name=>name, -class=>class);

           $widget->PathName;

           $widget->optionAdd(pattern=>value  ?,priority?);

           $widget->optionClear;

           $widget->optionGet(name, class);

           $widget->optionReadfile(fileName ?,priority?);

DESCRIPTION

       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