Q163185: PRB: Error with FILTER or WHERE Including This or Thisform
Article: Q163185
Product(s): Microsoft FoxPro
Version(s): 3.0 3.0b 5.0 6.0
Operating System(s):
Keyword(s): kbvfp300 kbvfp500 kbvfp600
Last Modified: 26-AUG-1999
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 5.0, 6.0
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SYMPTOMS
========
Upon browsing or skipping through a table with a filter condition set, or
through a cursor created with SQL SELECT and a WHERE condition, you may see one
of several errors:
Object is not contained in a FORM.
-or-
Object is not contained in a FORMSET.
-or-
THIS can only be used within a method.
-or-
THISFORM can only be used within a method.
-or-
Property <form or formset property holding filter value> is not found.
CAUSE
=====
These errors are caused by the record pointer being moved or the table being
browsed outside of the object where the FILTER or WHERE condition has been
stored in a form or object property. Regardless of where the FILTER condition is
set, or how the record pointer is being moved, the FILTER condition is
reevaluated each time the record pointer is moved. If the table or cursor is
being accessed outside the form or other object where THISFORM.<property>
or THIS.<property> is a valid reference, one of these errors occurs.
RESOLUTION
==========
To prevent these errors, use macro substitution, or store or reference the
FILTER or WHERE condition in a manner where it is always a valid reference.
You can do this in several ways:
- Set the FILTER condition with macro substitution, for example:
THISFORM.cfilterstring = "cust_id = 'A'"
lcFilterstring = THISFORM.cfilterstring
SET FILTER TO &lcFilterstring
- Store the FILTER condition to a public variable, for example:
PUBLIC gcFilterString
gcFilterString = "cust_id = 'A'"
SET FILTER TO (gcFilterString)
- Store the FILTER condition in a property of an object with a reference in a
public variable. There is an example of this below in MORE INFORMATION.
- If the error is caused by a WHERE condition in a cursor created with SELECT -
SQL, the NOFILTER keyword may be used in Visual FoxPro 5.0 to force a
temporary table to be used, rather than a filtered subset of the full table.
Here, the WHERE is never reevaluated after the SELECT is executed, for
example:
SELECT * FROM customer WHERE cust_id = "A" ;
INTO CURSOR custcursor NOFILTER
In Visual FoxPro 3.0, this can be forced by adding a calculated field to the
SELECT, such as the following:
SELECT *, SPACE(1) FROM customer WHERE cust_id = "A" ;
INTO CURSOR custcursor
STATUS
======
This behavior is by design.
MORE INFORMATION
================
Within a particular object or form references can be made, within that object's
code, to the object itself or the form or formset containing it, with THIS,
THISFORM, or THISFORMSET. These references are valid only within code that is
contained within these objects or their members. Because of the nature of SET
FILTER or a SELECT - SQL WHERE condition (when the returned records are a
filtered set of records), when either of these is the case the FILTER or WHERE
condition must contain references that are always valid.
Steps to Reproduce Behavior
---------------------------
1. Run the following code from a program (.prg) file:
* Beginning of code example
*
PUBLIC oNavClass, oform
oNavClass=CREATEOBJECT('navclass')
oform=CREATEOBJECT("form1")
oform.SHOW
DEFINE CLASS navclass AS CUSTOM
* This class does skipping and browsing in currently
* selected table
cfilterstring = ""
PROCEDURE DoBrowse
BROWSE NOWAIT
ENDPROC
PROCEDURE DoSkip
LPARAMETER ndirection
SKIP (ndirection)
IF EOF()
GO BOTTOM
ENDIF
IF BOF()
GO TOP
ENDIF
ENDPROC
ENDDEFINE
DEFINE CLASS form1 AS FORM
cfilterstring = ""
AUTOCENTER = .T.
HEIGHT = 200
WIDTH = 300
CAPTION = "Form1"
NAME = "FORM1"
ADD OBJECT combo1 AS COMBOBOX WITH ;
HEIGHT = 24, ;
LEFT = 12, ;
STYLE = 2, ;
TOP = 72, ;
WIDTH = 100, ;
NAME = "Combo1", ;
ROWSOURCE = "SELECT DISTINCT SUBSTR(cust_id,1,1) ;
FROM customer ORDER BY 1 INTO CURSOR curTemp", ;
ROWSOURCETYPE = 3
ADD OBJECT command1 AS COMMANDBUTTON WITH ;
TOP = 120, ;
LEFT = 60, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Skip", ;
NAME = "Command1"
ADD OBJECT text1 AS TEXTBOX WITH ;
CONTROLSOURCE = "customer.cust_id", ;
HEIGHT = 23, ;
LEFT = 180, ;
TOP = 72, ;
WIDTH = 100, ;
NAME = "Text1"
ADD OBJECT command2 AS COMMANDBUTTON WITH ;
TOP = 120, ;
LEFT = 168, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Skip -1", ;
NAME = "Command2"
ADD OBJECT command3 AS COMMANDBUTTON WITH ;
TOP = 170, ;
LEFT = 110, ;
HEIGHT = 27, ;
WIDTH = 84, ;
CAPTION = "Browse", ;
NAME = "Command3"
PROCEDURE LOAD
USE HOME()+'samples\data\customer'
ENDPROC
PROCEDURE UNLOAD
SET FILTER TO
USE IN customer
RELEASE oNavClass
ENDPROC
PROCEDURE combo1.INIT
THIS.VALUE = THIS.LIST(1)
ENDPROC
PROCEDURE combo1.VALID
THISFORM.cfilterstring = "cust_id = '"+THIS.VALUE+"'"
SET FILTER TO EVAL(THISFORM.cfilterstring)
* Comment out above 2 lines and remove comments from lines
* below to demonstrate workaround. ONavClass is public
* and its properties will always be in scope
* oNavClass.cfilterstring = 'cust_id = "'+THIS.VALUE+'"'
* SET FILTER TO EVAL(oNavClass.cfilterstring)
GO BOTTOM
GO TOP
THISFORM.REFRESH
ENDPROC
PROCEDURE command1.CLICK
oNavClass.DoSkip(1)
THISFORM.REFRESH
ENDPROC
PROCEDURE command2.CLICK
oNavClass.DoSkip(-1)
THISFORM.REFRESH
ENDPROC
PROCEDURE command3.CLICK
oNavClass.DoBrowse
ENDPROC
ENDDEFINE
*
* End of code example
2. A form appears. Make a selection from the drop-down list. The first record
matching the condition is displayed in the text box.
3. Press any of the three command buttons to navigate through the records or
browse the filtered list. The following error occurs:
Object is not contained in a FORM.
4. Ignore the error, close the form, and edit the .prg file. As noted in the
comments within the combo1.VALID procedure, comment out the lines storing the
filter condition as a property of the form, and uncomment the lines storing
the filter condition into a property of oNavClass.
5. Rerun the form, repeat steps 2 and 3 above, and no error will occur.
REFERENCES
==========
Visual FoxPro 5.0 Help File
Additional query words:
======================================================================
Keywords : kbvfp300 kbvfp500 kbvfp600
Technology : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b kbVFP500 kbVFP600
Version : 3.0 3.0b 5.0 6.0
=============================================================================
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