PRB: Null Values Disappear When Selected in a Grid or Browse

RESOLUTION

To display a text string ".NULL." for the currently selected field, create a column class that displays a label with the text string ".NULL." via the column's DynamicCurrentControl property. Copy the following code into TESTNULL.PRG, and then run it. You will see a grid with one column and 10 rows. Some of the rows contain numeric values, and some contain ".NULL." as a text string. Press DOWN ARROW to move through the records, note that the text string value of ".NULL." is displayed when the pointer is on a record that contains a null value.

  PUBLIC oForm
  oForm = CREATEOBJECT('myform')
  oForm.SHOW

  DEFINE CLASS mytextbox AS textbox
     SpecialEffect = 1
     BorderStyle = 0
     FontBold = .F.

     PROCEDURE keypress
     LPARAMETERS nKeyCode, nShiftAltCtrl

       IF nKeyCode = 48
         REPLACE testnull.name WITH .NULL.
         This.Value = ".NULL."
         NODEFAULT
       ENDIF
     ENDPROC
  ENDDEFINE

  DEFINE CLASS mytextbox1 AS mytextbox
     ControlSource = "testnull.name"
  ENDDEFINE

  DEFINE CLASS mytextbox2 AS mytextbox
     ControlSource = "This.Value"
     Value = ".NULL."

     PROCEDURE gotfocus
        This.Value = ".NULL."
     ENDPROC

     PROCEDURE lostfocus
        IF This.Value <> ".NULL."
           REPLACE testnull.name WITH This.Value
        ENDIF
     ENDPROC
  ENDDEFINE

  DEFINE CLASS mycolumn AS column
     DynamicCurrentControl = "IIF(ISNULL(testnull.name),'text2', 'text1')"
     Sparse = .f.
     Bound = .f.

     ADD OBJECT text1 AS mytextbox1
     ADD OBJECT text2 AS mytextbox2
  ENDDEFINE

  DEFINE CLASS mygrid AS grid
     RecordSource = ALIAS()
     ADD OBJECT c1 AS mycolumn
  ENDDEFINE

  DEFINE CLASS myform AS form
     ADD OBJECT g1 AS mygrid

     PROCEDURE load
        DELETE FILE testnull.dbf
        CREATE TABLE testnull (name c(10) NULL)

        FOR cnt = 1 to 10
          APPEND BLANK
          REPLACE name WITH IIF(MOD(RAND()*100, 2) >=1, SYS(3), .NULL.)
        ENDFOR
        GO TOP
     ENDPROC

     PROCEDURE unload
        CLOSE DATA ALL
     ENDPROC
  ENDDEFINE
				

   CREATE TABLE test (name C(10) NULL)
   APPEND BLANK
   REPLACE name WITH "Harry"
   APPEND BLANK
   REPLACE name WITH .NULL.
   BROWSE