datagrid update

[leghalbon]

hi there, im using the following code to load data into a datagrid and update it, but the update part isnt working fine, any ideas?

Dim conn As New OleDbConnection(connection_str)
conn.Open()
sql_str = "select * from num"

Dim objCommand As New OleDbCommand(sql_str, conn)

Dim DS As New DataSet()

data_adapter = New OleDbDataAdapter(objCommand)
data_adapter.Fill(ds, "to")

DataGrid1.DataSource = ds.Tables("to")

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'Dim ds As New DataSet()

If ds.HasChanges() Then
MsgBox("yes")
End If



the error msg is :
An unhandled exception of type 'System.NullReferenceException' occurred in datagridexple.exe

Additional information: Object reference not set to an instance of an object.


thank you.

[Lunatic3]

Your code has some problems:
1-I dont see any need for 'conn.Open()' in second line.
2- What you mean by update, if you mean to update the database, i see no update code.
3-In click event 'ds' is not decalred, so you face Nullreference excpetion.

[leghalbon]

im getting the error in the click code:

if ds.haschanges() ----

ds is allready declared in form_load,
im checking if the dataset has changes then im gonna update, and the error is keep on showing!

thank u.

[Lunatic3]

I think you need to learn more about the scope of variables. The variable not declared as public in a private Sub will remain private to that sub and not accecible by others.

[Pirate]

Then ds is not accessible from the click event . Better you declare it public .

[leghalbon]

thank u all for yr replies, it just was stupid from me not to realize it!

cld u tell tell me whats the code behind updating the datagrid on the button_click event. ill make sure i buy a dot net book but in the mean while i cld really use any available help.
thank you

[Lunatic3]

There are some ways to perform an update. But all of those need an update/insert command. Just as a quciky first declare your adapter and dataset public. then use a command builder to build the adapters update, delete, and insert commands. then u can update yourt database using data_adapter.Update(ds, "to")

Search this forum for command builder and you will find how to use it. Use the search below the posts not the one in the above blue band.

[dynamic_sysop]

if you have updated your access table / dataset then just doing this :

data_adapter.Fill(ds, "to")'/// fill with the updated stuff
DataGrid1.DataSource = ds.Tables("to")

should update the stuff in the datagrid.

[Lunatic3]

Oh my bad, I thought he is talking of updating the database.