Usually when you have a control is null error, the user has closed the window while an event is still running that references that control.

Hi Troy;

   The DWO is run at "arms length" from either its DW or DataStore Control container. So it's not feasible to use an IsValid() or IsNull() command on the DWO directly in many cases. In my framework though, I use a simple Describe() command that - if it fails - indicates that the DWO within those controls is not present.  HTH

Regards ... Chris

Have you tried IsValid instead of IsNull ?

Can you show us the full error message?

Maybe the problem is not that your datawindow 'is null', but you're trying to access a non existing column (misspelled?) or a non existing row number.

Also can you show us some code?

regards

Will dw_grid.dataobject come to any use here?
Will checking the result for empty or null solves the issue?

Happiness Always
BKR Sivaprakash

Hi Troy,

You've already got a lot of information about your problem.

Using the Yield() function is always dangerous because it changes the order how code usually runs.

For example: It may be that the user clicks a button or the window close "X". With Yield() Powerbuilder runs the code to close the window with all controls. After that the code after Yield() runs but it looses its context.

So if you use Yield() it is up to you to prevent the user from doing dangerous things.

What I usually do:

// instance variable
boolean ib_running = FALSE

-------------------------------------------------------

// the loop
ib_running = TRUE
DO WHILE ...
   Yield()

   // if you want a way to stop the loop
   IF NOT ib_running THEN
      // user stopped the loop
      EXIT
   END IF

   // here your code for the loop

LOOP
ib_running = FALSE

--------------------------------------------------------

// clicked event in a button to stop the loop (if you want it)
ib_running = FALSE

--------------------------------------------------------

// closequery event of the window
// do not allow to close the window if you are in a running loop
IF ib_running THEN return 1

HTH,

René