windows-xp/Source/XPSP1/NT/admin/netui/mprui/doc/olbdes.txt

                              NT User Interface
                               Design Overview
                           N-Level Outline Listbox
                          Kevin LaChapelle (KevinL)
                            Revision 0.5 10/06/91



1.  SCOPE

    This document provides a general design overview of the N-Level
    Outline listbox design.

2.  REFERENCES

    BLT Specification

3.  OVERVIEW

    The current design for the OLB does not contain a data structure
    other than that of the underlying windows listbox.  This has
proven to be inadequate for a n-level implementation for several
reasons that are not discussed here.  The key area that needed
improvement was how to insert an element into the listbox and have it
placed in the proper location.  The reason that this has proven
difficult is because it is possible for elements to have identical
"parent" values.  (In the case of Multiple networks the server/domain
names can be identical across domains).

    The solution to this problem is to have an underlying data
structure that takes the form of a tree.  Specifically one that has
the following structure:

       LBI  * plbi
       BOOL fShowChildren  // Display children (if any)
       NODE * pnParent     // Parent
       NODE * pnChild	   // First Child
       NODE * pnLeft	   // Left and Right
       NODE * pnRight      //    Siblings

The benefits of using a tree are many:

	- You will always know based upon your location in the tree
what index in the listbox you are.  (The tree is always sorted, and
thus provides a way to easily count the path from the root.)

	- This allows for easy preservation of selection across refreshes.

	- Easy way for to purge unwanted data from memory.
		For example:  If someone expands a node, then chooses
to collapse that node.  A pointer to that node could be entered into
a list for cleanup.  This list would contain pointers to parents
whose children were no longer visible and after an appropriate time
delay that information would be purged.  Of course at the moment it
would be too dificult to delete anything more than one level of
expansion because if the user happens to expand that node again we
must present the same expansion as was there before.

EXAMPLE:

ABLE TO PURGE:

       domain
           server
           server
           server
           server
           server
       domain1

domain is collapsed

       domain
       domain1

after a period of time all of the servers are purged.  If the user
expands domain then we reload the servers.


UNABLE TO PURGE:

       domain
           server
           server
           server
	      share
	      share
	      share
           server
           server
       domain1

domain is collapsed

       domain
       domain1

after a period of time the servers can't be purged because we would
then have to remember the level of expansion of each server because
if the user re-expands domain, then we should show what was there
before the initial collapse.

4.  CLASS HEIRARCHY

    The C++ classes for implementing the OLB is as follows:

        LB_TREE
	LBNODE
	LBI


5.  CLASS DETAILS

    T.B.F.I

6.  OPERATION

7.  OPEN ISSUES

8.  REVISION HISTORY

    Who         When        What
    ---         ----        ----
    KevinL      10/06/1991  Created this document.