ConfigSpecs(3pm) User Contributed Perl Documentation ConfigSpecs(3pm)NAMETk::ConfigSpecs - Defining behaviour of 'configure' for composite
widgets.
SYNOPSIS
sub Populate
{
my ($composite,$args) = @_;
...
$composite->ConfigSpecs('-attribute' => [ where,dbName,dbClass,default ]);
$composite->ConfigSpecs('-alias' => '-otherattribute');
$composite->ConfigSpecs('DEFAULT' => [ where ]);
$composite->ConfigSpecs($subwidget->ConfigSpecs);
...
}
$composite->configure(-attribute => value);
DESCRIPTION
The aim is to make the composite widget configure method look as much
like a regular Tk widget's configure as possible. (See Tk::options for
a description of this behaviour.) To enable this the attributes that
the composite as a whole accepts needs to be defined.
Defining the ConfigSpecs for a class.
Typically a widget will have one or more calls like the following
$composite->ConfigSpecs(-attribute => [where,dbName,dbClass,default]);
in its Populate method. When ConfigSpecs is called this way (with
arguments) the arguments are used to construct or augment/replace a
hash table for the widget. (More than one -option=>value pair can be
specified to a single call.)
dbName, dbClass and default are only used by ConfigDefault described
below, or to respond to 'inquiry' configure commands.
It may be either one of the values below, or a list of such values
enclosed in [].
The currently permitted values of where are:
'ADVERTISED'
Apply configure to advertised subwidgets.
'DESCENDANTS'
Apply configure recursively to all descendants.
'CALLBACK'
Setting the attribute does "Tk::Callback->new($value)" before
storing in "$composite->{Configure}{-attribute}". This is
appropriate for "-command => ..." attributes that are handled by
the composite and not forwarded to a subwidget. (E.g. Tk::Tiler has
"-yscrollcommand" to allow it to have scrollbar attached.)
This may be the first of several 'validating' keywords (e.g. font,
cursor, anchor etc.) that core Tk makes special for C code.
'CHILDREN'
Apply configure to all children. (Children are the immediate
descendants of a widget.)
'METHOD'
Call "$cw->attribute(value)"
This is the most general case. Simply have a method of the
composite class with the same name as the attribute. The method
may do any validation and have whatever side-effects you like. (It
is probably worth 'queueing' using afterIdle for more complex side-
effects.)
'PASSIVE'
Simply store value in "$composite->{Configure}{-attribute}".
This form is also a useful placeholder for attributes which you
currently only handle at create time.
'SELF'
Apply configure to the core widget (e.g. Frame) that is the basis
of the composite. (This is the default behaviour for most
attributes which makes a simple Frame behave the way you would
expect.) Note that once you have specified ConfigSpecs for an
attribute you must explicitly include 'SELF' in the list if you
want the attribute to apply to the composite itself (this avoids
nasty infinite recursion problems).
$reference (blessed)
Call $reference->configure(-attribute => value)
A common case is where $reference is a subwidget.
$reference may also be result of
Tk::Config->new(setmethod,getmethod,args,...);
Tk::Config class is used to implement all the above keyword types.
The class has "configure" and "cget" methods so allows higher level
code to always just call one of those methods on an object of some
kind.
hash reference
Defining:
$cw->ConfigSpecs(
...
-option => [ { -optionX=>$w1, -optionY=>[$w2, $w3] },
dbname dbclass default ],
...
);
So "$cw->configure(-option => value)" actually does
$w1->configure(-optionX => value);
$w2->configure(-optionY => value);
$w3->configure(-optionY => value);
'otherstring'
Call
$composite->Subwidget('otherstring')->configure( -attribute => value );
While this is here for backward compatibility with Tk-b5, it is
probably better just to use the subwidget reference directly. The
only case for retaining this form is to allow an additional layer
of abstraction - perhaps having a 'current' subwidget - this is
unproven.
Aliases
"ConfigSpecs( -alias => '-otherattribute' )" is used to make
"-alias" equivalent to "-otherattribute". For example the aliases
-fg => '-foreground',
-bg => '-background'
are provided automatically (if not already specified).
Delegating all options of a widget class to a subwidget
$composite->ConfigSpecs($subwidget->ConfigSpecs);
The above generates a list of composite ConfigSpecs arguments, one for
each valid option in $subwidget's class, and delegates said option to
$subwidget. See Tk::Widget and the widget method ConfigSpecs.
Duplicating composite ConfigSpecs and widget ConfigSpecs keys will
yield undefined results.
Default values
When the Populate method returns ConfigDefault is called. This calls
$composite->ConfigSpecs;
(with no arguments) to return a reference to a hash. Entries in the
hash take the form:
'-attribute' => [ where, dbName, dbClass, default ]
ConfigDefault ignores 'where' completely (and also the DEFAULT entry)
and checks the 'options' database on the widget's behalf, and if an
entry is present matching dbName/dbClass
-attribute => value
is added to the list of options that new will eventually apply to the
widget. Likewise if there is not a match and default is defined this
default value will be added.
Alias entries in the hash are used to convert user-specified values for
the alias into values for the real attribute.
New()-time configure
Once control returns to new, the list of user-supplied options
augmented by those from ConfigDefault are applied to the widget using
the configure method below.
Widgets are most flexible and most Tk-like if they handle the majority
of their attributes this way.
Configuring composites
Once the above have occurred calls of the form:
$composite->configure( -attribute => value );
should behave like any other widget as far as end-user code is
concerned. configure will be handled by Tk::Derived::configure as
follows:
$composite->ConfigSpecs;
is called (with no arguments) to return a reference to a hash
-attribute is looked up in this hash, if -attribute is not present in
the hash then 'DEFAULT' is looked for instead. (Aliases are tried as
well and cause redirection to the aliased attribute). The result
should be a reference to a list like:
[ where, dbName, dbClass, default ]
at this stage only where is of interest, it maps to a list of object
references (maybe only one) foreach one
$object->configure( -attribute => value );
is evaled.
Inquiring attributes of composites
$composite->cget( '-attribute' );
This is handled by Tk::Derived::cget in a similar manner to configure.
At present if where is a list of more than one object it is ignored
completely and the "cached" value in
$composite->{Configure}{-attribute}.
is returned.
CAVEATS
The "-background" and "-foreground" option values are automatically
propagated down to all composite widget's children. This may be
sometimes not desirable, especially if some subwidgets should use own
color schemes, either by using explicit options or by option database
definitions. If this is the case, then just add
-foreground => 'SELF',
-background => 'SELF',
to "ConfigSpecs".
It is the author's intention to port as many of the "Tix" composite
widgets as make sense. The mechanism described above may have to evolve
in order to make this possible, although now aliases are handled I
think the above is sufficient.
SEE ALSO
Tk::composite, Tk::options, Tk::Widget
perl v5.26.0 2017-07-22 ConfigSpecs(3pm)
