I found the root cause and a solution. There appears to be a difference in
the way the databinding works on an edit versus an add new. The dataset's
item collection is updated when I repopulate the SubClass combobox during an
Edit, but it is NOT updated when I repopulate the SubClass combobox during
an Add new. (It is updated just fine if I actually select something from the
SubClass combo in either case.)
Just before the EndCurrentEdit is executed, I can look at the SubClass
combobox SelectedValue property and the dataset item collection and see that
when editing an existing record, the two items have the same value. When
adding a new record, the SelectedValue property is correct and the dataset
item is NULL. It appears that the EndCurrentEdit, repopulates the bound
SubClass combobox, during an edit with the correct data, and during an add
new with a null. The update method that follows takes whatever is in the
dataset's item collection and sends it to the database.
My workaround was actually quite simple. Prior to executing the
EndCurrentEdit I set the dataset item collection entry to the value
contained in the SubClass combobox's SelectedValue property. Now the
EndCurrentEdit no longer sets the SelectedValue property to nothing AND the
update method sends the correct data to the database.
Whew!!!!! Two 14 hour days latter and I'm on to the next bug. <grin>
Gary
"Gary Shell" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> I have a pair of combo boxes on a form. Both have their SelectedValue
> property bound to a column on a table called "Input_Output". One column is
> called "Class" and the second is called "SubClass". Each combobox has its
> datasource, displaymember and SelectedValue member bound to separate
tables
> thru individual datatsets thru individual data adapters. The two tables
are
> "Class" and "SubClass".
>
> I use parameterized query to populate the list portion of the SubClass
Combo
> box based on the selection displayed in the Class combobox. When editing
> existing records everything works just fine. I can select a new Class and
> the SubClass combobox list content changes as expected. The text
displayed
> in the SubClass combo changes to the first item in the list, EVEN IF NO
> SELECTION IS MADE IN THE SUBCLASS COMBO. Updates to the data adapter
> successfully update the database. So far so good.
>
> If I attempt to ADD a new record, I have trouble. Initially the Class
combo
> and SubClass comboboxes are blank. Selecting an item in the Class combo
> cause the SubClass combobox to be repopulated, with the first entry
> displayed. When I execute the following code the SubClass combobox
> immediately goes blank:
>
> Me.BindingContext(Me.DsInput_Output, "Input_Output").EndCurrentEdit()
> If DsInput_Output.HasChanges(DataRowState.Added) Then
> 'only if there really are adds to be processed
> sqldaInput_Output.Update(Me.DsInput_Output)
> strTheItem = Me.cmbIO_Name.Text
> End If
>
> The SubClass combo actually goes blank on the EndCurrentEdit method. So,
of
> course, the database gets a null for that column when the Update method is
> executed. If I set a breakpoint on the EndCurrentEdit I can see that the
> SubClass combo box TEXT, and SELECTEDVALUE properties both have the
expected
> string value. After the EndCurrentEdit they are NOTHING.
>
> Now the strange part. If I actually select an item in the SubCLass combo
the
> EndCurrentEdit and subsequent code work just fine. Why is this explicit
> selection necessary? Why is the EndCurrentEdit setting the SelectedValue
> property to nothing? I'm confused and frustrated.
>
> Google searches have turned up little, except to note that apparently the
> combobox is a bit buggy. Specifically when placed on a tab page. (And
you
> guessed it, I am using these on a tab page. Sigh.)
>
> Anyone else fought this battle? Anyone win? Should I just use a third
> party combobox and cut my losses?
>
> Thanks,
> Gary
>
>
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