ExternView(3U)						    InterViews Reference Manual 					    ExternView(3U)

NAME

       ExternView, PreorderView, InorderView, PostorderView - base class for external representation objects and subclasses for common traversals

SYNOPSIS

       #include <Unidraw/Components/externview.h>

DESCRIPTION

       ExternView  is  the  abstract  base  class for external representation objects.	Generally speaking, external representation objects convey
       domain-specific information outside the editor.	They are simply component views that extract information from their subject and  external-
       ize it as a stream of bytes; thus the ExternView base class is derived from ComponentView.

       There  are three predefined ExternView subclasses: PreorderView, InorderView, and PostorderView.  These subclasses manage subviews and sup-
       port three common traversals of the external view hierarchy.

EXTERNVIEW PUBLIC OPERATIONS

       virtual boolean Emit(ostream&)
       virtual boolean Definition(ostream&)
	      Emit and Definition make up the basic ExternView protocol.  Emit initiates external representation generation and  calls	Definition
	      on  each	of  its children.  Emit normally calls the external view's own Definition operation first.  Then if the external view con-
	      tains subviews, Emit invokes the children's Definition operations in the proper order to ensure  a  syntactically  correct  external
	      representation.  Both of these operation do nothing by default, and both return a boolean that indicates whether the stream of bytes
	      was generated successfully.

       ExternView* GetView(Iterator)
       void SetView(ExternView*, Iterator&)
	      These operations do nothing by default.  Subclasses that contain children should redefine them as follows: GetView should return the
	      ExternView  to  which an iterator points.  SetView should initialize the iterator to point to a particular ExternView in the list of
	      children; it should initialize the iterator to point to a nil instance if the given ExternView is not a child.

EXTERNVIEW PROTECTED OPERATIONS

       ExternView(Component* = nil)
	      The abstract base class constructor is protected to guard against instantiation.	It takes the subject as an optional argument.

DERIVED CLASSES

       PreorderView, InorderView, and PostorderView redefine their Definition operations to perform preorder, inorder, and postorder traversals of
       their  children, respectively. Each child's Definition operation is called during the traversal.  Note that every child must be an instance
       of the same ExternView subclass to ensure a consistent traversal order.

SEE ALSO

       Component(3U), ComponentView(3U), Iterator(3U), ostream(3C++)

Unidraw 							  19 January 1991						    ExternView(3U)