Class: CompactHierarchicalItem

• Inheritance
• Description
• Class protocol
  • class initialization
  • queries
• Instance protocol
  • private
  • protocol-displaying
• Private classes

Inheritance:

   Object
   |
   +--AbstractHierarchicalItem
      |
      +--AbstractHierarchicalItemWithModel
         |
         +--CompactHierarchicalItem

Package:

stx:libwidg2

Category:

Views-Support

Version:

rev: 1.9 date: 2021/01/20 13:01:55

user: cg

file: CompactHierarchicalItem.st directory: libwidg2

module: stx stc-classLibrary: libwidg2

Description:

Compact Hierarchical Items are a new, tuned and optimized version of the original
hierarchical item, which suffers various problems:
    1) the old item did not store the model, which in many situations leads to very
       poor performance (it walks along the super-item hierarchy to find the model,
       which makes many algorithms O(n^2) instead of O(n)
       Has been refactored in the meantime, so my superclass holds the model now.
    2) it keeps individual width/height information, where this could be shared if
       many items have the same extent.
    3) it uses separate width/height instvars, where this information can be stored more compact
       in single integer (using bit-masks)
    4) it uses a separate boolean for the isExpanded, which could be encoded more space efficient as a single bit

Problems 2-4 only apply to huge trees with (say 100s of thousands of items). Such big trees are encountered
for example in the expecco activity log.

This class solves those issues:
    - it uses a compact width/height representation (bit masks in an integer), for
      items within a reasonable size (0 to 64k pixels wide, 0 to 16k pixels high).
    - falls back to a separate width/height holding object, if ever exceeded (which is unlikely)

    - it encodes the expanded state in a single bit

    - it uses the saved slot to allow for the model to be kept locally

Notice, that in order to be backward compatible, the cached width and height fields can
take integer values AND nil. Nil is typically used to mark an invalid cached value.
Here, the nil case is encoded in the bitField as all-ones (max value).

Before changing the superclass of your existing HierarchicalItem subclass, make sure that the subclass does not access 
the instvars isExpanded, width and heigh directly.
Instead, use the getters isExpanded, width and height and the setters setExpanded:, width: and height:

copyright
COPYRIGHT (c) 1999 by eXept Software AG
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Class protocol:

 initialize

I will pack width and height into a single integer

 isAbstract

Return if this class is an abstract class.
True is returned here for myself only; false for subclasses.
Abstract subclasses must redefine this again.

Instance protocol:

 makeWidthAndHeightUnknown

invalidate any cached with/height information

 setExpanded: aBoolean

set expanded flag without any computation or notification

 getWidthAndHeightOn: aGC

fetch the width and height from my label, if it is to be displayed on aGC

 height

return the cached height

 heightOn: aGC

return the height of the receiver, if it is to be displayed on aGC

 isExpanded

(comment from inherited method)
returns true if the item is expanded

 width

return the cached width

 width: w height: h isExpanded: expanded

encode width and height, and isExpanded state.
Tries to use a single integer to encode all three of them,
saving a lot of memory for big trees.

 widthOn: aGC

return the width of the receiver, if it is to be displayed on aGC

Private classes:

    Geometry