Save/SET/Restore of SET Environment Settings (130306)

MORE INFORMATION

The class "cSET" demonstrates this technique. In this class, a number of the current SET environment settings for DELETED, ALTERNATE, and DECIMALS are stored in objects. One object is created for each environment setting that should be stored. This class could easily be expanded to include additional environment settings.

When the class, cSET, is instantiated in your form or other application component, an object is created for each desired environment setting. The CONSTRUCTOR method is invoked whenever you want to change an environment setting. It creates a command string that sets the desired temporary environment setting. When the instantiated class object is released, the DESTRUCTOR method is called. This method restores each environment setting to its state at the time cSET was instantiated.

1. To use this approach in an application, begin by creating a program that contains the class definition.

      * Begin code example
      * Save This as CSET.PRG
      * This class provides SET environment save/SET/restore capabilities
      * When the class is instantiated, the current SET environment is
      * saved & SET to the desired value. When the instantiated object goes
      * out of scope, the environment is restored.
   
      * Usage:
      *  CreateObject( "CSET", <cExpr1>, <cExpr2> | <nExpr2> [, <cExpr3>] )
      *
      *   cExpr1 = One of the SET commands
      *   cExpr2 = Appropriate character value for the SET command
      *   nExpr2 = Appropriate numeric value for the SET command
      *   cExpr3 = Optional character value for SET commands that are both
      *            ON | OFF
      *            and have another value (like ALTERNATE, FIELDS, etc.)
      *
      * Examples:
      *   loDeletedSave   = createobject( "CSET", "deleted", "on" )
      *   loDecimalsSave  = createobject( "CSET", "decimals", 5 )
      *   loAlternateSave = createobject( "CSET", "alternate", "on", ;
      *                     "alter.txt")
   
      DEFINE CLASS CSET AS CUSTOM
   
      * PROTECTED Data Members
      * =====================================================
      PROTECTED mcSET               && SET command
      PROTECTED muOrgValue          && Original value of the SET
      PROTECTED muOrgValue1         && Original secondary value of the SET
   
      * Public Data Members
      * ========================================================
      * NONE
   
      * PROTECTED Function Members
      * =================================================
   
      * Constructor Method
      * ----------------------------------------------------------
   
      PROTECTED FUNCTION Init
      PARAMETER pcSET, puNewValue, pcNewValue1
   
      LOCAL lnParmCount          && number of PARAMETERs sent to init
      LOCAL lcSETCommand            && constructed SET command
   
      lnParmCount = PARAMETERS()
   
      * Default the data members
      This.mcSET = ""
      This.muOrgValue = ""
      This.muOrgValue1 = ""
   
      IF ( lnParmCount < 2 )
      *   This.error( "some error" )
         RETURN
      ENDIF
   
      * Save current environment
   
      This.mcSET       = pcSET
      This.muOrgValue  = SET( pcSET )
      This.muOrgValue1 = SET( pcSET, 1 )
      IF ( This.muOrgValue == This.muOrgValue1 )
         * throw This away because we don't need it
         This.muOrgValue1 = ""
      ENDIF
   
      IF ( lnParmCount = 3 )
         * optional argument handling
         lcSETCommand = pcSET + " to " + pcNewValue1
         SET &lcSETCommand
      ENDIF
   
      IF ( TYPE( "This.muOrgValue" ) == 'C' )
         * character type of SET
         lcSETCommand = puNewValue
         IF ( ! INLIST( This.muOrgValue, "ON", "OFF" ) )
            * not a simple ON|OFF so add a TO keyword
            lcSETCommand = "TO " + puNewValue
         ENDIF
      ELSE
         * numeric type of SET
         lcSETCommand = "TO " + STR( puNewValue )
      ENDIF
   
      lcSETCommand = pcSET + " " + lcSETCommand
      SET &lcSETCommand                          && change the SET
   
      * Destructor Method
      * ---------------------------------------------------- ------
      PROTECTED function Destroy
   
      *LOCAL lcSETCommand            && constructed SET command
   
      IF ( EMPTY( This.mcSET ) )
         RETURN
      ENDIF
   
      IF ( TYPE( "This.muOrgValue" ) == 'C' )
         * character type of SET
         lcSETCommand = This.muOrgValue
         IF ( ! INLIST( This.muOrgValue, "ON", "OFF" ) )
            * not a simple ON|OFF so add a TO keyword
            lcSETCommand = "TO " + This.muOrgValue
         ENDIF
      ELSE
         * numeric type of SET
         lcSETCommand = "TO " + STR( This.muOrgValue )
      ENDIF
   
      lcSETCommand = This.mcSET + " " + lcSETCommand
      SET &lcSETCommand                              && restore the SET
   
      IF ( ! EMPTY( This.muOrgValue1 ) )
         * restore secondary SET information
         lcSETCommand = This.mcSET + " TO " + This.muOrgValue1
         SET &lcSETCommand
      ENDIF
   
      * Public Function Members
      * ====================================================
   
      * Value Method
      * ---------------------------------------------------------------
   
      * RETURN the current values of the PROTECTED data members in a comma
      * delimited string.
   
      FUNCTION Value
      LOCAL lcRETURNValue
   
      IF ( TYPE( "This.muOrgValue" ) == 'C' )
         lcRETURNValue = This.mcSET + "," + This.muOrgValue
      ELSE
         lcRETURNValue = This.mcSET + "," + ;
            ALLTRIM( STR( This.muOrgValue ) )
      ENDIF
   
      IF ( ! EMPTY( This.muOrgValue1 ) )
         lcRETURNValue = lcRETURNValue + "," + This.muOrgValue1
      ENDIF
   
      RETURN lcRETURNValue
   
      ENDDEFINE
   
      *** END CODE EXAMPLE FOR cSET.PRG
   						

2. Create a program with the following code. This code would normally be placed in the load event of a form, or at the top of a .PRG file. For the purposes of demonstration, it is being placed in a separate program file:

      ******************************************************************
      *Begin code example
      ******************************************************************
   
      * Driver program to test CSET class
   
      SET PROCEDURE TO cset ADDITIVE
   
      CLEAR
      SET DELETED ON       && start it out on for testing
   
      _Screen.Show
      ? "Deleted:", SET("deleted")
      loDeletedSave = CreateObject( "CSET", "deleted", "off" )
      ? "Value:", loDeletedSave.Value()
      ? "Deleted:", SET("deleted")
   
   						

3. Run the program created in step 2. The following values should be displayed on the screen:

      Deleted: ON
      Value: deleted, ON
      Deleted: OFF