Combobox and dataset

[Raine]

I am trying to populate a combobox from a dataset but I am getting the following error: System.NullReferenceException, object reference not set to an instance of an object.

here's my code, can't see where I failed to instantiate.

Dim dad = New OleDbDataAdapter
Dim ds As DataSet
Dim strConn, strSQL As String

strConn = "Data Source=Data3;Integrated Security=SSPI"
strSQL = "Select instNbr from MyTable"
dad = New SqlClient.SqlDataAdapter(strSQL, strConn)
ds = New DataSet
dad.Fill(ds)
cboInstNbr.DataSource = ds.Tables("MyTable")
cboInstNbr.DisplayMember = ds.Tables("MyTable").Columns("instNbr").ToString

the error occurs on the displaymember line of code.

Help a newbie with VB.Net.
Thanks!

[Pirate]

Try this line as it's (don't change it)

cboInstNbr.DisplayMember = "TABLE_NAME"

[Raine]

No error message but my combobox is not populated with the field. I am under the assumption that displaymember is the field name your populating the combobox with. So how come it won't populate?

[Pirate]

D'uh . It's my fault . I mean change it to this (where xxx is the name of your column):

cboInstNbr.DataSource = ds.Tables("MyTable").DefaultView
cboInstNbr.DisplayMember = "xxxx"

[Raine]

I changed the following code to this:

cboInstNbr.DataSource = ds.Tables("MyTable")
cboInstNbr.DisplayMember = "instnbr"

When I added defaultview it gave me the aformentioned error on the datasource line instead this time. I tested the code to see if it would populate a data grid and it had no problem doing that. It just won't work on a combobox. Is there something else that needs to be done for a combobox to get it running?

[Pirate]

umm , have you tried "ValueMember" in place of "DisplayMember" ?

[Raine]

Yes. Do you know how to populate the combobox another way?

[Pirate]

Originally posted by Raine
Yes. Do you know how to populate the combobox another way?

Yes , I'll create demo for you . I'll be back .

[Swatz]

Try changing this line
cboInstNbr.DataSource = ds.Tables("MyTable")
To
cboInstNbr.DataSource = ds.Tables(0)

Frank

[Pirate]

Here's the demo .

[taxes]

Hi,

I'm probably nearly as new as you but I don't think that Pirate's suggestions would deal with the error message you had. It does puzzle me that the error message disappeared at one stage. Without seeing your entire code I have to make a few guesses.

I assume you have imported the OLEDB namespace. If not ,

Dim dad = New OleDbDataAdapter

should be

Dim dad = New Oledb.OleDbDataAdapter


Also, instead of

dad.Fill(ds)

try

dad.Fill(ds, "myTable").

Make sure you have opened your connection

[Raine]

Thanks it works....my only question is what does TableStr represent? I left it out and it works fine.

[Pirate]

Originally posted by Raine
Thanks it works....my only question is what does TableStr represent? I left it out and it works fine.

It's the table's name that you want to get the data from !