PRB: Access/Assign Not Called by DIMENSION, ADEL or AINS

MORE INFORMATION

The Access and Assign methods are new in Visual FoxPro 6.0. In effect, they allow you to attach events to properties. When the property's value(s) are queried (Access method), or when the property's values are set (Assign method), you can execute user code. Because of the nature of arrays and their manipulation, the Access and Assign methods associated with the array properties behave differently than with non-array properties.

Steps to Reproduce Behavior

The following program instantiates a form from a form class definition. The form contains an array property. The array is populated in the form's Load method. A row is deleted from the array, the array is redimensioned, and a row is added back into the array.

1. Run the following code from a program (.prg) file:

         Clear
         DEBUG
         _SCREEN.Show()
         DEBUGOUT " "
         DEBUGOUT " "
         oform1=NEWOBJECT("form1")
         DEBUGOUT " "
         oform1.PrintToScreen      && Output contents of array to screen
         =adel(oform1.atest,2)     && Deletes 2nd row
         DIME oform1.atest[alen(oform1.atest,1)-1,alen(oform1.atest,2)]
         DEBUGOUT " "
         oform1.PrintToScreen
         DIME oform1.atest[alen(oform1.atest,1)+1,alen(oform1.atest,2)]
         =ains(oform1.atest,2)     && insert before 2nd row
         DEBUGOUT " "
         oform1.PrintToScreen
   
         DEFINE CLASS form1 AS form
   
            Caption = "Form1"
            Name = "Form1"
            DIMENSION atest[3,2]
   
            PROCEDURE atest_access
               LPARAMETERS m.nIndex1,m.nIndex2
               * Echo current program and calling program to
               * Debug Output window
               DEBUGOUT "In " + PROGRAM()+", called from " ;
                  + PROGRAM(PROGRAM(-1)-1)
               RETURN THIS.atest[m.nIndex1,m.nIndex2]
            ENDPROC
   
            PROCEDURE atest_assign
               LPARAMETERS vNewVal,m.nIndex1,m.nIndex2
               * Echo current PROGRAM and calling PROGRAM to
               * Debug Output window
               DEBUGOUT "In "+PROGRAM()+", called from " ;
                  + PROGRAM(PROGRAM(-1)-1)
               this.atest[m.nIndex1,m.nIndex2] = m.vNewVal
            ENDPROC
   
         PROC PrintToScreen
            ?'    Column 1   Column 2'
            * Iterate through array and print each element
            FOR lnRow = 1 to alen(this.atest, 1)
               ?
               FOR lnCol = 1 to alen(this.atest, 2)
                  ??this.atest[lnRow, lnCol]
               ENDFOR
            ENDFOR
            ?
         PROCEDURE Load
            * Populate the array
            FOR lnRow = 1 to alen(this.atest, 1)
               FOR lnCol = 1 to alen(this.atest, 2)
                  this.atest[lnRow, lnCol] = 100 * lnRow + lnCol
               ENDFOR
            ENDFOR
   
           ENDPROC
         ENDDEFINE
    
   						

2. The contents of the array is printed to the Visual FoxPro desktop three times by the PrintToScreen method. The first printing is the original contents. The second printing contains the contents after the second row is deleted and the third row is removed by the DIMENSION command. The third printing is the contents after a third row is added with DIMENSION and a new second row is inserted.
3. The DEBUGOUT command is used to output information to the Debug Output Window. The current program echos (either the Access or Assign method) and the calling program, one program back in the call stack, is returned by PROGRAM(PROGRAM(-1)-1)). Here you see that the atest_assign was called six times from the form Load method. The Atest_access was called six times, then four times, then six times as the three calls to PrintToScreen are executed.