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MGH_WIDGET_SELF

MGH_WIDGET_SELF

Name


  MGH_WIDGET_SELF

Purpose


  Support the retrieval of object refernces from, and the storing of object
  references in, structures of type MGH_WIDGET_SELF. These are associated with
  the UVALUE of a widget element, to provide a bridge between the widget tree
  and an associated widget object.

Category


  Widgets.

Calling Sequence


  There are three modes of operation, controlled by the type of the positional
  argument and keywords:
  1: Store an object reference in an MGH_WIDGET_SELF structure
      struct = MGH_WIDGET_SELF(STORE_OBJECT=objref)
  2: Retrieve an object reference from an MGH_WIDGET_SELF structure
      objref = MGH_WIDGET_SELF(struct, FOUND=found)
  3: Search for an MGH_WIDGET_SELF structure in the children of widgetID, then
      retrieve and return the object reference.
      objref = MGH_WIDGET_SELF(widgetID, FOUND=found)

Positional Parameters


  arg
    A scalar of type structure (calling sequence 2) or integer
    (calling sequence 3). Ignored for calling sequence 3.

Keyword Parameters


  FOUND
    For calling sequences 2 & 3 this keyword returns 1 if an object
    reference has been found otherwise 0. Note that the object
    reference may not be valid, even if FOUND is 1.
  STORE_OBJECT
    Set this keyword to an object reference to select calling sequence 3.

Outputs


  Depends on calling sequence.
  THE CONVENTIONS FOR STORING MGH_WIDGET_SELF STRUCTURES
  The classes that currently store MGH_WIDGET_SELF structures are MGH_GUI_Base
  and MGH_GUI_PDmenu. They store the structure in the UVALUE of the first or
  second child of the object's base widget (BASE property). The widget tree
  is set up--with some difficulty, I might add--so that this widget never
  generates events. (If it did, then the UVALUE might be needed for storing
  callback structures.) It can't always be the first child because on top-level
  bases this would be the menu-bar base and we definitely do want to use callbacks
  for that.
  As a slight generalisation, the MGH_WIDGET_SELF function (calling
  sequence 3) looks for the structure in *all* the children of the widget.

Comment


  Yes, I agree that it is ugly to bundle three fundamentallly
  different modes of operation in one function. I do it this way
  because I want to keep things localised and IDL has no suitable
  larger units of organisation than functions.
###########################################################################
  This software is provided subject to the following conditions:
  1. NIWA makes no representations or warranties regarding the
    accuracy of the software, the use to which the software may
    be put or the results to be obtained from the use of the
    software. Accordingly NIWA accepts no liability for any loss
    or damage (whether direct of indirect) incurred by any person
    through the use of or reliance on the software.
  2. NIWA is to be acknowledged as the original author of the
    software where the software is used or presented in any form.
###########################################################################

Modification History


  Mark Hadfield, Jun 2001:
    Written.



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