Q194514: PRB: Cannot Pass Array Property of Form by Reference to OLE DLL

Article: Q194514
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbCOMt kbvfp600
Last Modified: 24-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
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SYMPTOMS
========

Trying to pass an array property of a form by reference to a COM server results
in the following error:

  "Alias 'THISFORM' is not found"

RESOLUTION
==========

There are two methods of working around this limitation:

1. Use the ACOPY() function to copy all the data from the array property to an
  array variable, then pass the array variable by reference.

  -or-

2. If having the array be a property is not a necessity, eliminate the array
  property, and dimension an array variable in the Init of the form. Pass that
  array by reference to the object.

  Example 1:

  Modify the btnOne.Click Method to the following:

           ***************Start Code Workaround 1****************
           PROCEDURE btnOne.CLICK
              THISFORM.oArrTest=CREATEOBJECT('frmArray.ArrTest')
              IF TYPE('thisform.oArrTest')#'O' then
                  WAIT WINDOW 'Did not instantiate'
                 RETURN
              ENDIF
              COMARRAY(thisform.oArrTest,11)
              ACOPY(THISFORM.MyArray,aTemp)
              THISFORM.oArrTest.modarray(@aTemp)
              DISPLAY MEMORY LIKE aTemp
           ENDPROC
           PROCEDURE btnClose.CLICK
              CLEAR EVENTS
              RELEASE THISFORM
           ENDPROC
           **********End Code Workaround 1********************

  Example 2:

  Replace the Client code with the following:

        ***************Start Code Workaround 2********************
        x=CREATEOBJECT("Test1")
        x.VISIBLE=.T.
        x.SHOW
        READ EVENTS

        DEFINE CLASS Test1 AS FORM OLEPUBLIC
           oArrTest=.NULL.
           ADD OBJECT btnOne AS COMMANDBUTTON WITH TOP = 1, ;
              CAPTION = 'Test Array'
           ADD OBJECT btnClose AS COMMANDBUTTON WITH TOP = 25, ;
              CAPTION = 'Close'
           PROCEDURE INIT
           DIMENSION aMyArray(5,1)
              I=1
              FOR I = 1 TO 5
                 aMyArray(I)='Form'
              ENDFOR
           ENDPROC

           PROCEDURE btnOne.CLICK
              THISFORM.oArrTest=CREATEOBJECT('frmArray.ArrTest')
              IF TYPE('thisform.oArrTest')#'O' then
                  WAIT WINDOW 'Did not instantiate'
                 RETURN
              ENDIF
              COMARRAY(thisform.oArrTest,11)
              THISFORM.oArrTest.modarray(@aMyArray)
              DISPLAY MEMORY LIKE aMyArray
           ENDPROC
           PROCEDURE btnClose.CLICK
              CLEAR EVENTS
              RELEASE THISFORM
           ENDPROC
        ENDDEFINE
        *************End Code Workaround 2*************************

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Place the following Class Definition code in a program file attached to a
  project called frmArray:

        ****************Begin Class Definition*********
        DEFINE CLASS ArrTest AS CUSTOM OLEPUBLIC
           PROCEDURE modarray
              PARAMETERS MyArray
              EXTERNAL ARRAY MyArray
              FOR I = 1 TO 5
                 MyArray(I)="COM"
               ENDFOR
           ENDPROC
        ENDDEFINE
        **************End Class Definition************

2. Build the project into a COM DLL.

3. Place the following Client Code in a program file and run it:

        ***************Client Code Start*******************
        x=CREATEOBJECT("Test1")
        x.VISIBLE=.T.
        x.SHOW
        READ EVENTS

        DEFINE CLASS Test1 AS FORM OLEPUBLIC
           DIMENSION MyArray(5)
           oArrTest=.NULL.
           ADD OBJECT btnOne AS COMMANDBUTTON WITH TOP = 1, ;
              CAPTION = 'Test Array'
           ADD OBJECT btnClose AS COMMANDBUTTON WITH TOP = 25, ;
              CAPTION = 'Close'
           PROCEDURE INIT
              I=1
              FOR I = 1 TO 5
                 MyArray(I)='Form'
              ENDFOR
           ENDPROC

           PROCEDURE btnOne.CLICK
              THISFORM.oArrTest=CREATEOBJECT('frmArray.ArrTest')
              IF TYPE('thisform.oArrTest')#'O' then
                  WAIT WINDOW 'Did not instantiate'
                 RETURN
              ENDIF
              COMARRAY(thisform.oArrTest,11)
              THISFORM.oArrTest.modarray(@THISFORM.MyArray)
              DISPLAY MEMORY LIKE THISFORM.MyArray
           ENDPROC
           PROCEDURE btnClose.CLICK
              CLEAR EVENTS
              RELEASE THISFORM
           ENDPROC
        ENDDEFINE
        *****************Client Code End************************

4. When the form appears, press the "btnOne" button, and note the error message.

Additional query words: kbVFP600 kbComt

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Keywords          : kbCOMt kbvfp600 
Technology        : kbVFPsearch kbAudDeveloper kbVFP600
Version           : WINDOWS:6.0
Issue type        : kbprb

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