Subform load order and "Invalid reference to the property Form"

[John Hunter]

I've recently had a nasty problem with the "Invalid reference to the
property Form" error in subforms - nasty because it doesn't seem to
consistently happen to all forms which contain the same structure and
code. Judging by the forums I've researched, it's not an uncommon
error. I'm happy to say I've found a simple solution.

OVERVIEW: I have a main form (no record source) which contains two
subforms. The subforms are not linked, but there is some code in Sub1
which finds a related record in Sub2. The problem is that the
OnCurrent event in Sub1 runs BEFORE Sub2 has loaded, so the first time
it causes an "Invalid reference to the property Form" error. I trap
for the error, then Sub2 loads, and everything works from this point.

CAUSE: subforms are controls, and they run their events before the
Main forms events. So the sequence of events when I open the Main form
is
Sub1: Open, Load, Activate, Current
Sub2: Open, Load, Activate, Current
Main: Open, Load, Activate, Current
The problem occurs in some forms and not others because of the order I
originally placed the subforms on them!

SOLUTION: Sub2 needs to load before Sub1, so that the code in the Sub1
OnCurrent event can reference it. Unfortunately, there is no load
sequence property for subforms, and the Tab Order property doesn't
affect the sequence of loading. However, you can influence the load
order!
1) remove the subforms from Main and save it. For good measure I also
did a compact and repair
2) add Sub2 to Main and Save it. Being paranoid, I did another compact
and repair
3) add Sub1 to Main and Save it. Now it works and I can get rid of the
error trapping!

[Allen Browne]

John, thanks for posting the cause and the solution. It is satisfying to
solve, and anyone who searches groups.google.com will find your solution.

Yes, of course one of the subforms must load before the other, and trying to
refer to the one that has not loaded yet will cause an error. I have a
little disquiet, though at the idea that the load sequence is actually
stable and does not need the error handling. It seems like the kind of thing
that might come back to bite you one day, e.g. if you have to repair a
corruption by importing everything into a new database, or convert to a new
version?

Would it be worthwhile leaving the error-handling for the particular
situation in place?

--
Allen Browne - Microsoft MVP. Perth, Western Australia.
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

"John Hunter" <js******@waikato.ac.nz> wrote in message
news:6b**************************@posting.google.c om...

I've recently had a nasty problem with the "Invalid reference to the
property Form" error in subforms - nasty because it doesn't seem to
consistently happen to all forms which contain the same structure and
code. Judging by the forums I've researched, it's not an uncommon
error. I'm happy to say I've found a simple solution.

OVERVIEW: I have a main form (no record source) which contains two
subforms. The subforms are not linked, but there is some code in Sub1
which finds a related record in Sub2. The problem is that the
OnCurrent event in Sub1 runs BEFORE Sub2 has loaded, so the first time
it causes an "Invalid reference to the property Form" error. I trap
for the error, then Sub2 loads, and everything works from this point.

CAUSE: subforms are controls, and they run their events before the
Main forms events. So the sequence of events when I open the Main form
is
Sub1: Open, Load, Activate, Current
Sub2: Open, Load, Activate, Current
Main: Open, Load, Activate, Current
The problem occurs in some forms and not others because of the order I
originally placed the subforms on them!

SOLUTION: Sub2 needs to load before Sub1, so that the code in the Sub1
OnCurrent event can reference it. Unfortunately, there is no load
sequence property for subforms, and the Tab Order property doesn't
affect the sequence of loading. However, you can influence the load
order!
1) remove the subforms from Main and save it. For good measure I also
did a compact and repair
2) add Sub2 to Main and Save it. Being paranoid, I did another compact
and repair
3) add Sub1 to Main and Save it. Now it works and I can get rid of the
error trapping!