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Weighted Redraws for Faster Processing/Less Flickering
When developing complicated components and windows setting the redraw can become a problem. You run into problems when a higher level function calls a lower level function and both needed to alter the redraw of the object. The lower level function is not always called by a higher level function and so needs to alter the redraw property. For example the higher level function switched off the redrawing of the window and performs some processing without any problems. It then calls a lower level function which also switches off the redraw. After the lower level function is complete it sets redraw back to true and returns to the higher level function. The higher level functions continues processing expecting the redraw to be switched off but it is not because the lower level function has re-enabled it.

To fix this problem you can add a weight to the setredraw function. This software trick remembers how many times a function is called and only unsets the real setting when an equal number of unsettings have been called.

Declare a protected instance variable:Integer ii_redraw. Then overload the SetRedraw function where ab_setting is the single input argument of type Boolean:

IF ab_Setting THEN
   ii_redraw --
   IF ii_redraw <= 0 THEN
      ii_redraw = 0
      super::SetRedraw( TRUE )
      RETURN 1
   ii_redraw ++
   IF ii_redraw = 1 THEN &
      super::SetRedraw( FALSE )


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Ken Howe 2011