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

• Microsoft Visual FoxPro for Windows, version 6.0

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

Keywords : kbCOMt kbVFp600
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbprb