Error after removing row and then adding new row to datatable

11 Apr 2005 12:01 AM

diesel

Ok, once again I'm at my wits' end with a VB.Net problem.

I have a button which opens a wizard that allows the user to enter a
new record to a table. I have a datatable called dtItems that stores
the data from a table named Items, and a dataview called dvItems that
is a sorted subset of the data in dtItems. I have a datagrid called
(yes, you guessed it) dgItems, which has dvItems as its datasource.

When the user hits the New Item button, a new row is created with the
code:

rowNewItem = dtItems.NewRow

I set some default values for the fields in the row, and then add the
row to dtItems like so:

dtItems.Rows.Add(rowNewItem)

Then the wizard form opens. The user can enter data on the form, and
when they hit Add Item the wizard closes and the row gets updated with
the data they entered. That all works fine.

The problem occurs when the user cancels the wizard and I want to
remove the new row. I do this with:

dtItems.Rows.Remove(rowNewItem)

This seems to work, but then if the user clicks the New Item button
again, I get the dreaded "object reference not set to an instance of an
object" error on the dtItems.Rows.Add(rowNewItem) line, even though I
have checked in the debugger to make sure that both dtItems and
rowNewItem are valid object references. I have also tried setting
rowNewItem to nothing before recreating it, but it makes no difference.

It seems like it's trying to reuse the deleted row for some reason.
Has anyone else run into this?

Any help would be much appreciated.

11 Apr 2005 4:28 AM

Adam Goossens

Diesel,

What does the stack trace say? It may actually be something inside the
DataTable.Add method that is the problem, not dtItems and rowNewItem.

You might even want to try not adding the row unless the user completes
the wizard successfully. If they cancel, simply don't add it.

Let me know how you go.

Regards
-Adam.

diesel wrote:
Show quoteHide quote

> Ok, once again I'm at my wits' end with a VB.Net problem.
>
> I have a button which opens a wizard that allows the user to enter a
> new record to a table. I have a datatable called dtItems that stores
> the data from a table named Items, and a dataview called dvItems that
> is a sorted subset of the data in dtItems. I have a datagrid called
> (yes, you guessed it) dgItems, which has dvItems as its datasource.
>
> When the user hits the New Item button, a new row is created with the
> code:
>
> rowNewItem = dtItems.NewRow
>
> I set some default values for the fields in the row, and then add the
> row to dtItems like so:
>
> dtItems.Rows.Add(rowNewItem)
>
> Then the wizard form opens. The user can enter data on the form, and
> when they hit Add Item the wizard closes and the row gets updated with
> the data they entered. That all works fine.
>
> The problem occurs when the user cancels the wizard and I want to
> remove the new row. I do this with:
>
> dtItems.Rows.Remove(rowNewItem)
>
> This seems to work, but then if the user clicks the New Item button
> again, I get the dreaded "object reference not set to an instance of an
> object" error on the dtItems.Rows.Add(rowNewItem) line, even though I
> have checked in the debugger to make sure that both dtItems and
> rowNewItem are valid object references. I have also tried setting
> rowNewItem to nothing before recreating it, but it makes no difference.
>
>
> It seems like it's trying to reuse the deleted row for some reason.
> Has anyone else run into this?
>
> Any help would be much appreciated.
>

11 Apr 2005 6:31 AM

Cor Ligthert

Diesel,

Probably is this because you declare your rowNewItem somewhere globaly. Try
to avoid that as much as possible, by instance by doing this.

\\\
dim rowNewItem as datarow = dtItems.NewRow
////

I hope this helps,

Cor

11 Apr 2005 2:55 PM

diesel

Hmm. I had thought of that, but I wasn't sure how to get around it,
since I have to be able to modify the row from the wizard. I guess
I'll have to create a new dataview in the wizard and somehow filter it
to find the new record, rather than trying to modify rowNewItem from
the wizard directly.

Thanks so much for the help, Adam/Cor. I will look at the code again
tonight and let you know how it goes.

Thanks again,
Diesel