Question

Can anyone tell me How do I solve this error.
Error: NullReferenceException was Unhandled – “Object reference not set to an instance of an object.”
Line: Dim reader As OleDbDataReader = dbCommand.ExecuteReader()
Database: MS Access
IDE: VB 2010 Express

Imports System.Data.OleDb
Imports System.Data.SqlClient
Imports System


Public Class Form1       
Dim dbConnection As OleDbConnection        
Dim dbCommand As OleDbCommand       
Dim strInsert As String       
Dim dbDataAdapter As OleDbDataAdapter        
Dim ConnectString As String = "Provider = Microsoft.Jet.OLEDB.4.0;" & "Data Source =atg.mdb"

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub


Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

 dbConnection = New OleDbConnection(ConnectString) 'here I use the new keyword to initialize connection  
 dbConnection.Open()
 Dim command As New OleDbCommand("SELECT XX FROM ABC", dbConnection) ' initialize command and pass query and open connection to its constructor  
 Dim reader As OleDbDataReader = dbCommand.ExecuteReader() 'ERROR IS HERE
 Do While (reader.Read()) ' loop here until reader finish reading and add every row to the list box  
        ListBox1.BeginUpdate()
        ListBox1.Items.Add(reader.Item("ABC"))             
        ListBox1.EndUpdate()
    Loop
    reader.Close()
    dbConnection.Close()
End Sub
End Class

Answer 1

Where you find dbCommand in dbCommand.ExecuteReader() statement.Use command.ExecuteReader() instead .

You didn’t initiate your dbCommand.You just Decalared it.What you did is creating another variable called command and initiated it.So try with this