PRB: Cannot Trap for Error #1739

• Microsoft Visual FoxPro for Windows, versions 3.0 and 3.0b

SYMPTOMS

Changing a property of a Cursor or Relational Object correctly initiates error #1739 "Property setting will not take effect until data environment reloaded." Unfortunately, the error cannot be trapped with an Error Event nor an ON ERROR command.

WORKAROUND

Avoid any possibility of getting the error. Always unload the Data Environment before changing the property. To unload the Data Environment, use the following steps to initiate the CloseTables method of the Data Environment:

1. Create a new property of the form called "DataLoad" with an initial value of False (.F.).

2. Inside the OpenTables method, include the following code:

   THISFORM.DataLoad=.T.

3. Inside the CloseTables method, include the following code:

   THISFORM.DataLoad=.F.

4. Use the DataLoad flag to check to see if the Data Environment has been loaded and act accordingly. In the following code, the Data Environment is unloaded before the Cursor property is changed. The code can be located inside any method or event of the form.

         IF THISFORM.DataLoad
            THISFORM.DataEnvironment.CloseTables
         ENDIF
         THISFORM.DataEnvironment.Cursor1.ALIAS="FOX"
   
      The DataLoad flag is used to determine if the data environment has been
      loaded because the CloseTables method will generate an error if the Data
      Environment had not first been loaded with the OpenTables method.
      OpenTables is called initially if AutoOpenTables is True (.T.).
   
   

STATUS

Microsoft is researching this behavior and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The following chart is a listing of all the current properties for the Data Environment, Cursor, and Relation objects. If the Data Environment has been loaded with the OpenTables method, the chart will show what will occur if an attempt is made to change the property. Although Error #1739 will occur for many of the Cursor and Relation objects, the value of the property will change and be in effect the next time the Data Environment is loaded.

Data Environment       Read Only      Error #1739         No Error

AutoCloseTables            X
AutoOpenTables             X
InitialSelectedAlias                                          X
Name                                                          X

Alias                                      X
Database                                   X
Name                                                          X
ReadOnly                                   X
BufferModeOverride                         X
Exclusive                                  X
NoDataOnLoad                               X
CursorSource                               X
Filter                                                        X
Order                                                         X

ChildAlias                                 X
OneToMany                                  X
ChildOrder                                 X
ParentAlias                                X
Name                                                          X
RelationalExpr                             X

Steps to Reproduce Behavior

1. Create a new form.

2. Add any table to the Data Environment of the form.

3. In the Load event for the form, type the following:

   ON ERROR WAIT WINDOW "This is an Error"

4. Run the form.

5. In the Command window, type the following:

   _SCREEN.Forms(1).DataEnvironment.Cursor1.Alias="FOX"

6. The ON ERROR routine does not activate. A FoxPro Error Message is displayed on the screen.