Combox SelectedValue databinding

styles00

Combox SelectedValue databinding

Visual Studio307
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

-

Gary

Registered User

Tue Jul 13 10:34:47 CDT 2004

Re:Combox SelectedValue databinding

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" <gshell@fuse.net>wrote in message

Quote

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