system.invalidoperationexception: Fill: selectCommand.Connection property has not been initialized - visual-studio

Question

I'm working on connecting the MS Access database in Visual basic. Unfortunately, I cannot link the records from my data base into visual basic.
My database is located at C:\Users\lenovo\Desktop\GUI references\WindowsApplication1\WindowsApplication1\bin\Debug
Database name is smsenabler.mdb
Table to be connected is ProfessorListTable
The table contains fields of
ID | LastName | FirstName | MI | Department | Year Employed
My codes on my form are shown below:
Imports System.Data.OleDb
Public Class ProfessorList
Dim con As OleDbConnection
Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label1.Click
End Sub
Private Sub ProfessorList_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
Dim con As OleDbConnection = New OleDbConnection
con.ConnectionString = "Provider = Microsoft.Jet.OLEDB.4.0; Data Source = ..\smsenabler.mdb"
con.Open()
showRecords()
con.Close()
Catch ex As Exception
MessageBox.Show(ex.ToString)
End Try
End Sub
Public Sub showRecords()
Dim dt As New DataTable
Dim ds As New DataSet
ds.Tables.Add(dt)
Dim da As New OleDbDataAdapter("Select * from ProfessorListTable", con)
da.Fill(dt)
Dim myRow As DataRow
For Each myRow In dt.Rows
ListView1.Items.Add(myRow.Item(0))
ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(myRow.Item(1))
ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(myRow.Item(2))
ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(myRow.Item(3))
ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(myRow.Item(4))
ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(myRow.Item(5))
Next
End Sub
ERROR MESSAGE
system.invalidoperationexception: Fill: selectCommand.Connection property has not been initialized. At System.Data.Common.DbDataAdapter.GetConnection3(DbDataAdapter adapter,IDbCommand command String method) at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables,Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataTable dataTable) at THESIS_GUI.ProfessorList.ProfessorList_Load(Object sender, EventArgs e) in C:\Users\lenovo\Desktop\GUI references\WindowsApplication1\WindowsApplication1\ProfessorList.vb:line17
LINE 17
showRecords()
It gives me an output with no records at all.It only shows a GUI with a field written on it. Thank you ..

Answer 1

One suggestion is to make sure your connection ('con') is available for all subroutines. I have used global variables before to prevent the need for opening and closing the connection (which would lead to problems in the old days). We both do a similar approach, but here is some code I have stripped bare (removed error traps, debug aids, etc.):
Global cnLocalData As ADODB.Connection
Public Sub Get_Connection()
Set cnLocalData = New ADODB.Connection
With cnLocalData
.Provider = "Microsoft.Jet.OLEDB.4.0"
.Properties("Data Source") = "C:\data\SomeDB.mdb"
.Open
End With
End Sub

Answer 2

you are disconnected to the server, you must open you connection in the showRecords method.
This error error appear when you want to execute a command with the closed connection.