"Object reference not set to an instance of an object" when exiting program

  1  Imports System.Data.SqlClient
  2  
  3  Public Class Form3
  4      Dim con As New SqlConnection
  5      Dim myconstring As String = "Data Source=ETA-TESTSRVR;Initial Catalog=Procurement;Integrated Security=True"
  6  
  7      Private Sub E2BindingNavigatorSaveItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles E2BindingNavigatorSaveItem.Click
  8  
  9          Me.Validate()
 10          Me.E2BindingSource.EndEdit()
 11          Me.TableAdapterManager.UpdateAll(Me.ProcurementDataSet)
 12  
 13      End Sub
 14  
 15      Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 16  
 17          'TODO: This line of code loads data into the 'ProcurementDataSet.E1' table. You can move, or remove it, as needed.
 18          Me.E1TableAdapter.FillBy1(Me.ProcurementDataSet.E1)
 19  
 20          'TODO: This line of code loads data into the 'ProcurementDataSet.E2' table. You can move, or remove it, as needed.
 21          Me.E2TableAdapter.Fill(Me.ProcurementDataSet.E2)
 22  
 23      End Sub
 24  
 25      Private Sub Mat_Sub_NoComboBox_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Mat_Sub_NoComboBox.SelectedIndexChanged
 26  
 27          con.ConnectionString = myconstring
 28  
 29          'Automated Serial Number
 30          Dim da As New SqlDataAdapter("SELECT max(sl_no)+1 as max FROM e1 where project_id='" + Project_IDTextBox.Text + "'", con)
 31          Dim dt As New DataTable
 32          da.Fill(dt)
 33          Sl_NoTextBox.Text = dt.Rows(0).Item("max").ToString
 34          If Sl_NoTextBox.Text = "" Then
 35              Sl_NoTextBox.Text = 1
 36          End If
 37  
 38          'Fetching Data to Textbox
 39          Dim da1 As New SqlDataAdapter("SELECT Project_ID,Trade,Fix,Material_Description FROM Mat_e1_prj where mat_sub_no='" + Mat_Sub_NoComboBox.SelectedValue.ToString + "'", con)
 40          Dim dt1 As New DataTable
 41          da1.Fill(dt1)
 42          Project_IDTextBox.Text = dt1.Rows(0).Item("Project_ID").ToString
 43          TradeTextBox.Text = dt1.Rows(0).Item("Trade").ToString
 44          FixTextBox.Text = dt1.Rows(0).Item("fix").ToString
 45          DescriptionTextBox.Text = dt1.Rows(0).Item("Material_Description").ToString
 46          
 47      End Sub
 48  
 49  End Class