PRB: Cannot Pass an Array Member to a Procedure

• Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

An array that is declared as a member of a class cannot be passed by reference to a function or a method. For example, if you declare an array as a property of a form, the error "Alias 'this' is not found" is displayed when a method is called as follows:

   This.pNewFunction(@this.atest)

CAUSE

Visual FoxPro always passes object properties by value. Object properties cannot be passed by reference.

WORKAROUND

An alternative is to pass the array name to a method, and manipulate the array or a copy of the array. The following example code defines a form with a command button. When the command button is clicked, a function is called that adds 10 to each element of an array declared as a property of the command button. The same method can be used in the Form Designer.

Sample Code

PUBLIC oform

oform=CREATEOBJECT('frmtest') oform.Show

DEFINE CLASS frmtest AS FORM

   ADD OBJECT cmd1 AS cmd

DEFINE CLASS cmd AS COMMANDBUTTON DIMENSION aprop[10] PROCEDURE init

   LOCAL ii
   FOR ii = 1 TO 10
      This.aprop[ii]=ii
   ENDFOR

PROCEDURE click

   LOCAL ii
   THIS.ADDEM(This, 'aprop')
   ACTIVATE SCREEN
   FOR ii =1 TO 10
      ?This.aprop[ii]
   ENDFOR

* Two parameters are passed to the procedure: a reference to the object, * and the array name. PROCEDURE ADDEM

   LPARAMETERS oref, cprop
   local ii, atemp[1]

   =ACOPY(oref.&cprop,atemp)  & Makes a copy of the member array.

   FOR ii = 1 TO aLEN(oref.&cprop)
      atemp[ii]=atemp[ii] + 10
   ENDFOR

   =ACOPY(atemp,oref.&cprop)

STATUS

This behavior is by design.