option(n) [incr Tcl] option(n)______________________________________________________________________________NAME
itcl::option - define options for extendedclass, widget or widgetadap‐
tor
Parts of this description are "borrowed" from Tcl extension [snit], as
the functionality is mostly identical.
WARNING!
This is new functionality in [incr Tcl] where the API can still
change!!
SYNOPSIS
option optionSpec ?defaultValue?
option optionSpec ?options?
_________________________________________________________________DESCRIPTION
The option command is used inside an [incr Tcl] extendedclass/wid‐
get/widgetadaptor definition to define options.
In the first form defines an option for instances of this type, and
optionally gives it an initial value. The initial value defaults to the
empty string if no defaultValue is specified.
An option defined in this way is said to be locally defined. The
optionSpec is a list defining the option's name, resource name, and
class name, e.g.:
option {-font font Font} {Courier 12}
The option name must begin with a hyphen, and must not contain any
upper case letters. The resource name and class name are optional; if
not specified, the resource name defaults to the option name, minus the
hyphen, and the class name defaults to the resource name with the first
letter capitalized. Thus, the following statement is equivalent to the
previous example:
option -font {Courier 12}
See The Tk Option Database for more information about resource and
class names.
Options are normally set and retrieved using the standard instance
methods configure and cget; within instance code (method bodies, etc.),
option values are available through the options array:
set myfont $itcl_options(-font)
In the second form you can define option handlers (e.g., -config‐
uremethod), then it should probably use configure and cget to access
its options to avoid subtle errors.
The option statement may include the following options:
-default defvalue
Defines the option's default value; the option's default value
will be "" otherwise.
-readonly
The option is handled read-only -- it can only be set using con‐
figure at creation time, i.e., in the type's constructor.
-cgetmethod methodName
Every locally-defined option may define a -cgetmethod; it is
called when the option's value is retrieved using the cget
method. Whatever the method's body returns will be the return
value of the call to cget.
The named method must take one argument, the option name. For
example, this code is equivalent to (though slower than) Itcl's
default handling of cget:
option -font -cgetmethod GetOption
method GetOption {option} {
return $itcl_options($option)
}
Note that it's possible for any number of options to share a
-cgetmethod.
-cgetmethodvar varName
That is very similar to -cgetmethod, the only difference is, one
can define a variable, where to find the cgetmethod during run‐
time.
-configuremethod methodName
Every locally-defined option may define a -configuremethod; it
is called when the option's value is set using the configure or
configurelist methods. It is the named method's responsibility
to save the option's value; in other words, the value will not
be saved to the itcl_options() array unless the method saves it
there.
The named method must take two arguments, the option name and
its new value. For example, this code is equivalent to (though
slower than) Itcl's default handling of configure:
option -font -configuremethod SetOption
method SetOption {option value} {
set itcl_options($option) $value
}
Note that it's possible for any number of options to share a
single -configuremethod.
-configuremethodvar varName
That is very similar to -configuremethod, the only difference
is, one can define a variable, where to find the configuremethod
during runtime.
-validatemethod methodName
Every locally-defined option may define a -validatemethod; it is
called when the option's value is set using the configure or
configurelist methods, just before the -configuremethod (if
any). It is the named method's responsibility to validate the
option's new value, and to throw an error if the value is
invalid.
The named method must take two arguments, the option name and
its new value. For example, this code verifies that -flag's
value is a valid Boolean value:
option -font -validatemethod CheckBoolean
method CheckBoolean {option value} {
if {![string is boolean -strict $value]} {
error "option $option must have a boolean value."
}
}
Note that it's possible for any number of options to share a
single -validatemethod.
-validatemethodvar varName
That is very similar to -validatemethod, the only difference is,
one can define a variable, where to find the validatemethod dur‐
ing runtime.
KEYWORDS
option, widget, widgetadaptor, extendedclass
itcl 4.0 option(n)