NAME

Archetype - base class for all [incr Tk] mega-widgets

INHERITANCE

none

WIDGET-SPECIFIC OPTIONS

Name:	clientData
Class:	ClientData
Command-Line Switch:	-clientdata

This does not affect the widget operation in any way. It is simply a hook that clients can use to store a bit of data with each widget. This can come in handy when using widgets to build applications.

DESCRIPTION

The Archetype class is the basis for all [incr Tk] mega-widgets. It keeps track of component widgets and provides methods like "configure" and "cget" that are used to access the composite configuration options. Each component widget must be registered with the Archetype base class using the "itk_component add" method. When the component is registered, its configuration options are integrated into the composite option list. Configuring a composite option like "-background" causes all of the internal components to change their background color.

It is not used as a widget by itself, but is used as a base class for more specialized widgets. The Widget base class inherits from Archetype, and adds a Tk frame which acts as the "hull" for the mega-widget. The Toplevel base class inherits from Archetype, but adds a Tk toplevel which acts as the "hull".

Each derived class must invoke the itk_initialize method within its constructor, so that all options are properly integrated and initialized in the composite list.

PUBLIC METHODS

The following methods are provided to support the public interface of the mega-widget.

pathName cget option

Returns the current value of the configuration option given by option.

In this case, option refers to a composite configuration option for the mega-widget. Individual components integrate their own configuration options onto the composite list when they are registered by the "itk_component add" method.

pathName component ?name? ?command arg arg ...?

Used to query or access component widgets within a mega-widget. With no arguments, this returns a list of symbolic names for component widgets that are accessible in the current scope. The symbolic name for a component is established when it is registered by the "itk_component add" method. Note that component widgets obey any public/protected/private access restriction that is in force when the component is created.

If a symbolic name is specified, this method returns the window path name for that component.

Otherwise, the command and any remaining arg arguments are invoked as a method on the component with the symbolic name name. This provides a well-defined way of accessing internal components without relying on specific window path names, which are really details of the implementation.

pathName configure ?option? ?value option value ...?

Query or modify the configuration options of the widget. If no option is specified, returns a list describing all of the available options for pathName (see Tk_ConfigureInfo for information on the format of this list). If option is specified with no value, then the command returns a list describing the one named option (this list will be identical to the corresponding sublist of the value returned if no option is specified). If one or more option-value pairs are specified, then the command modifies the given widget option(s) to have the given value(s); in this case the command returns an empty string.

In this case, the options refer to composite configuration options for the mega-widget. Individual components integrate their own configuration options onto the composite list when they are registered by the "itk_component add" method.

PROTECTED METHODS

The following methods are used in derived classes as part of the implementation for a mega-widget.

itk_component add ?-protected? ?-private? ?--? name createCmds ?optionCmds?

Creates a component widget by executing the createCmds argument and registers the new component with the symbolic name name. The -protected and -private options can be used to keep the component hidden from the outside world. These options have a similar effect on component visibility as they have on class members.

The createCmds code can contain any number of commands, but it must return the window path name for the new component widget.

The optionCmds script contains commands that describe how the configuration options for the new component should be integrated into the composite list for the mega-widget. It can contain any of the following commands:

If the optionCmds script is not specified, the usual option-handling commands associated with the class of the component widget are used by default.

itk_component delete name ?name name ...?

Removes the component widget with the symbolic name name from the mega-widget. The component widget will still exist, but it will no longer be accessible as a component of the mega-widget. Also, any options associated with the component are removed from the composite option list.

Note that you can destroy a component using the destroy command, just as you would destroy any Tk widget. Components automatically detach themselves from their mega-widget parent when destroyed, so "itk_component delete" is rarely used.

itk_initialize ?option value option value...?

This method must be invoked within the constructor for each class in a mega-widget hierarchy. It makes sure that all options are properly integrated into the composite option list, and synchronizes all components to the initial option values. It is usually invoked near the bottom of the constructor, after all component widgets have been added.

If any option/value pairs are specified, they override settings determined from the X11 resource database. The arguments to the constructor are usually passed along to this method as follows:

itcl::class MyWidget {
    inherit Widget
    constructor {args} {
        .
        .
        .
        eval itk_initialize $args
    }
}

itk_option add optName ?optName optName ...?

Adds one or more options to the composite option list for a mega-widget. Here, optName can have one of the following forms:

Options are normally integrated into the composite option list when a component widget is first created. This method can be used to add options at a later time. For example, the Widget and Toplevel base classes keep only the bare minimum options for their "hull" component: -background and -cursor. A derived class can override this decision, and add options that control the border of the "hull" component as well:

itcl::class MyWidget {
    inherit Widget
    constructor {args} {
        itk_option add hull.borderwidth hull.relief
        itk_component add label {
            label $itk_interior.l1 -text "Hello World!"
        }
        pack $itk_component(label)
        eval itk_initialize $args
    }
}

itk_option define switchName resourceName resourceClass init ?config?

This command is used at the level of the class definition to define a synthetic mega-widget option. Within the configure and cget methods, this option is referenced by switchName, which must start with a "-" sign. It can also be modified by setting values for resourceName and resourceClass in the X11 resource database. The init value string is used as a last resort to initialize the option if no other value can be used from an existing option, or queried from the X11 resource database. If any config code is specified, it is executed whenever the option is modified via the configure method. The config code can also be specified outside of the class definition via the configbody command.

In the following example, a synthetic "-background" option is added to the class, so that whenever the background changes, the new value is reported to standard output. Note that this synthetic option is integrated with the rest of the "-background" options that have been kept from component widgets:

itcl::class MyWidget {
    inherit Widget
    constructor {args} {
        itk_component add label {
            label $itk_interior.l1 -text "Hello World!"
        }
        pack $itk_component(label)
        eval itk_initialize $args
    }
    itk_option define -background background Background #d9d9d9 {
        puts "new background: $itk_option(-background)"
    }
}

itk_option remove optName ?optName optName ...?

Removes one or more options from the composite option list for a mega-widget. Here, optName can have one of the forms described above for the "itk_option add" command.

Options are normally integrated into the composite option list when a component widget is first created. This method can be used to remove options at a later time. For example, a derived class can override an option defined in a base class by removing and redefining the option:

itcl::class Base {
    inherit itk::Widget
    constructor {args} {
        eval itk_initialize $args
    }
    itk_option define -foo foo Foo "" {
        puts "Base: $itk_option(-foo)"
    }
}
itcl::class Derived {
    inherit Base
    constructor {args} {
        itk_option remove Base::foo
        eval itk_initialize $args
    }
    itk_option define -foo foo Foo "" {
        puts "Derived: $itk_option(-foo)"
    }
}

PROTECTED VARIABLES

Derived classes can find useful information in the following protected variables.

itk_component(name)

The "itk_component" array returns the real window path name for a component widget with the symbolic name name. The same information can be queried using the component method, but accessing this array is faster and more convenient.

itk_interior

This variable contains the name of the window that acts as a parent for internal components. It is initialized to the name of the "hull" component provided by the Widget and Toplevel classes. Derived classes can override the initial setting to point to another interior window to be used for further-derived classes.

itk_option(option)

The "itk_option" array returns the current option value for the composite widget option named option. Here, the option name should include a leading "-" sign. The same information can be queried using the cget method, but accessing this array is faster and more convenient.

KEYWORDS

itk, Widget, Toplevel, mega-widget