The Toplevel class inherits everything from the Archetype class, and adds a Tk toplevel called the "hull" component to represent the body of the mega-widget. The window class name for the hull is set to the most-specific class name for the mega-widget. The protected variable itk_interior contains the window path name for the "hull" component. Derived classes specialize this widget by packing other widget components into the hull.

Since the hull for the Toplevel class is implemented with a Tk toplevel, mega-widgets in the Toplevel class have their own toplevel window. This class is used to create dialog boxes and other pop-up windows.


Suppose we want to create a MessageInfo mega-widget class that acts as a pop-up notice window. It displays a message which the user can dismiss by pressing the "Dismiss" button. If we had such a widget, we might use it like this:

    messageinfo .m -background blue -foreground white \
        -message "File not found:\n/usr/local/bin/foo"
and it would look like this:

screen snapshot of MessageInfo widget

Each time a new widget is created, the constructor is invoked automatically to create the internal component widgets. The "hull" component is created automatically by the itk::Toplevel base class. Other components can be packed into this. Each component must be created using the "itk_component add" method, as shown below. This method creates a component widget, gives it a symbolic name, and merges its options into the composite list for the mega-widget. Once a component has been created like this, its window path name can be referenced via its symbolic name as "$itk_component(name)".

The methods in the mega-widget class define the operations that the widget will respond to. In this example, there is a protected method centerOnScreen that is used internally to bring up the window in the middle of the screen.

option add *MessageInfo.title "Notice" widgetDefault

class MessageInfo {
    inherit itk::Toplevel

    constructor {args} {
        itk_component add dismiss {
            button $itk_interior.dismiss -text "Dismiss" \
                -command "destroy $itk_component(hull)"
        pack $itk_component(dismiss) -side bottom -pady 4

        itk_component add separator {
            frame $itk_interior.sep -height 2 -borderwidth 1 -relief sunken
        pack $itk_component(separator) -side bottom -fill x -padx 4

        itk_component add icon {
            label $itk_interior.icon -bitmap info
        pack $itk_component(icon) -side left -padx 8 -pady 8

        itk_component add infoFrame {
            frame $
        pack $itk_component(infoFrame) -side left -expand yes \
            -fill both -padx 4 -pady 4

        itk_component add message {
            label $itk_interior.mesg -width 20
        } {
            rename -text -message message Text
        pack $itk_component(message) -expand yes -fill both

        eval itk_initialize $args

        after idle [code $this centerOnScreen]

    protected method centerOnScreen {} {
        update idletasks
        set wd [winfo reqwidth $itk_component(hull)]
        set ht [winfo reqheight $itk_component(hull)]
        set x [expr ([winfo screenwidth $itk_component(hull)]-$wd)/2]
        set y [expr ([winfo screenheight $itk_component(hull)]-$ht)/2]
        wm geometry $itk_component(hull) +$x+$y

usual MessageInfo {
    keep -background -cursor -foreground -font
    keep -activebackground -activeforeground -disabledforeground
    keep -highlightcolor -highlightthickness

proc messageinfo {pathName args} {
    uplevel MessageInfo $pathName $args

Notice how the constructor takes widget configuration options as an "args" list, and passes these arguments to the itk_initialize method. Each derived class must invoke the itk_initialize method in this manner within its constructor , so that all options are properly integrated and initialized in the composite list.

It is a good idea to include the following things along with the mega-widget class definition: