Disable a date field if another is null (1 Viewer)

Hi,

I have two date fields on my form, for when a particular process is suspended and then unsuspended. Some processes will never be suspended, so in these cases I want to disable accidental input to the Unsuspended field.

I thought I could do it like this


but that gives me Run-time Error 424 Object required. This code is on the OnCurrent event by the way. I plan to have similar code on the AfterUpdate event of the Suspension field.

If I use = Null rather than Is Null then I don't get an error message, but it doesn't actually work, i.e. the Unsuspension field is enabled even if the Suspension field hasn't been completed.

I read something somewhere about a date never really being null, so I tried =0 Again, no error, but the disabling doesn't work.

Where am I going wrong here? In case it's relevant, the fields are on a form called "frm01Study" on TabCtl41 (which I never renamed) on a page called pgGlobal which is the second of three tabs.

Thanks,

Pat.

Is Null and IsNull() are different.. Is Null is used in SQL for Queries, whereas IsNull() is a VBA Function.. So try..
Null is not a value, so it cannot be compared with, by using Equals.. There are several ways you can tacke Null values.. Using Nz(), Len(theVariable & vbNullString) = 0.. I prefer the Len() method as it will not only catch Null but also Zero Length Strings..

You, sir, are a diamond!

The first one worked perfectly. As for the second, I'll admit I've never quite got the distinction between NULL and zero-length string (I assume you mean "") and I know this is something i ought to get to grips with. Manana!

Thank you.

you need to put this code in the forms current event

you also need ot add it to the dependent control's afterupdate event to unlock the field after data is entered.

which then begs the question ...

what if someone enters data in controlA - thereby unlocking the date.
then enters a date
then goes back and deletes the data in controlA?

That is a very good point! This is one of the challanges I face. The Rule based form concept.

Good documentation about this very subject seems to be rare. Any good demo's or papers to suggest would be welcome.

Thanks Dave -

I did mention in the first post that I plan to have similar code on the AfterUpdate event...but I needed help to get the code right first! ...so I will get round to that.

As for someone taking out a date they have previously entered, that also occurred to me. I haven't coded this yet - and I need to clear it with the manager of the staff who'll be using this - but I thought I would include a line such as... Unsuspended.value = null ...in the AfterUpdate event of the 'Suspended' control, basically overriding the unsuspension.