How to declare a connection object on a class level connection not in local scope with VB.NET? - sql-server

Question

I got the error:
Fill: SelectCommand.Connection property has not been initialized.
I think this is because I declare my data set not inside the private sub but in the public class.....
but I need to use the data set in more than once in different private sub during the program....how should I define it ?
many thanks.
Imports System.Data
Imports System.Data.SqlClient
Public Class Form1
Dim con As SqlConnection
Dim strsql As String
Dim da As New SqlDataAdapter(strsql, con)
Dim ds As New DataSet()
Dim strcon As String
Dim newmode As Boolean
Dim newrow As DataRow
Dim cb As SqlCommandBuilder
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
newmode = False
'Dim con As SqlConnection
'Dim strsql As String
con = New SqlConnection("initial catalog=test;data source=nazi;integrated security=sspi;")
strsql = "select*from table_1"
con.Open()
'Dim da As New SqlDataAdapter(strsql, con)
'Dim ds As New DataSet()
da.Fill(ds, "dd")
TextBox1.DataBindings.Add(New Binding("text", ds, "dd.tel"))
TextBox2.DataBindings.Add(New Binding("text", ds, "dd.nam"))
TextBox3.DataBindings.Add(New Binding("text", ds, "dd.address"))
da.update(ds, "dd")
con.Close()
End Sub
Private Sub empty()
textrecord.text = ""
TextBox1.text = ""
TextBox2.text = ""
TextBox3.text = ""
TextBox4.text = ""
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
newrow = ds.Tables("dd").NewRow
newmode = True
textrecord.BackColor = Color.Red
textrecord.Text = "new record"
MsgBox("enter new record and press save")
Call empty()
End Sub
End Class

Answer 1

Instead of:
Dim con As SqlConnection
try adding New:
Dim con As New SqlConnection("initial catalog=test;...")
However, it's best practice to only open a connection just before you need it, and close it right after. Connections should be local variables in Using blocks, not class variables!

Answer 2

You create the DataAdapter at the global level in this line
Dim da As New SqlDataAdapter(strsql, con)
but at this point in time your strsql is empty and if you change it afterwards it doesn't change inside the dataadatpter, thus the error message.
If you insist on keeping all that global vars (and it's considered a bad practice as #Andomar pointed out in is answer) then you should be sure to create the DataAdapter with the correct sqlstring just before its usage:
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
newmode = False
con = New SqlConnection("initial catalog=test;data source=nazi;integrated security=sspi;")
strsql = "select*from table_1"
con.Open()
da = New SqlDataAdapter(strsql, con) '<- added this line here '
da.Fill(ds, "dd")
....
con.Close()
End Sub