CODEWITHSUNDEEP
vb.netms-access-2013oledbcommandoledbdatareader
Aouie
Aouie

Reputation: 119

Object reference not set to an instance of an object VB.Net OleDbCommand

Everytime i search on my database it always says "Object reference not set to an instance of an object." Please anyone help me. Thank you.

Here is my code for Search:

Private Sub BtnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnSearch.Click

    If TBSearch.Text = "" Then
        MsgBox("Please enter keyword to search...", MsgBoxStyle.Information, "Keyword to search...")`
        TBSearch.Focus()
        Exit Sub
    End If
    Call OpenConnection()
    With OleDa
        Call Initialized()
        .SelectCommand = New OleDb.OleDbCommand() <-------- Error appears here.
        .SelectCommand.CommandText = "SELECT * FROM [HighSchool] WHERE [LastName] Like '%%" & TBSearch.Text & "%%' or [FirstName] Like '%%" & TBSearch.Text & "%%' or [MI] Like '%%" & TBSearch.Text & "%%'" & _
        "Or [Gender] Like '%%" & TBSearch.Text & "%%' or [Address] Like '%%" & TBSearch.Text & "%%' or [Birthday] Like '%%" & TBSearch.Text & "%%' or [RNumber] Like '%%" & TBSearch.Text & "%%'" & _
        "Or [ENumber] Like '%%" & TBSearch.Text & "%%'  ORDER By LastName ASC"
        .SelectCommand.Connection = OleCn

        Call PopulateListView()

        If Me.LV.Items.Count >= 1 Then
            MsgBox(Me.LV.Items.Count & " Record(s) found for " & "( " & Me.TBSearch.Text & " )", MsgBoxStyle.OkOnly, "Record(s) found...")
        Else
            MsgBox("No record(s) found for " & "( " & Me.TBSearch.Text & " )" & " , please try again... ", MsgBoxStyle.Critical, "No record found...")
            TBSearch.Focus()
            TBSearch.SelectAll()
        End If
    End With
    Call CloseConnection()
End Sub

Here is my code for Populate ListView:

Public Sub PopulateListView() Me.LV.Items.Clear() Dim OleDr As OleDb.OleDbDataReader OleDr = OleDa.SelectCommand.ExecuteReader()

    Do While OleDr.Read()
        Dim Item As New ListViewItem
        Item.Text = IIf(OleDr.IsDBNull(0), "", OleDr.Item(0))
        For shtCntr = 1 To OleDr.FieldCount() - 1
            If Not OleDr.IsDBNull(shtCntr) Then
                Item.SubItems.Add(OleDr.Item("FirstName"))
                Item.SubItems.Add(OleDr.Item("LastName"))
                Item.SubItems.Add(OleDr.Item("MI"))
                Item.SubItems.Add(OleDr.Item("Gender"))
                Item.SubItems.Add(OleDr.Item("Address"))
                Item.SubItems.Add(OleDr.Item("Birthday"))
                Item.SubItems.Add(OleDr.Item("RNumber"))
                Item.SubItems.Add(OleDr.Item("ENumber"))
            Else
                Item.SubItems.Add("")
            End If
        Next shtCntr
        Me.LV.Items.Add(Item)
    Loop
End Sub

Upvotes: 0

Views: 525

Answers (1)

Jonathan Allen
Jonathan Allen

Reputation: 70337

Ok, let's fix some stuff.

  1. Don't use Call. That's just a hold-over from VB 6 (i.e. the late 90's)
  2. Don' use Exit Sub. Use Return instead. (Same reason as #1)

  3. Use parameterized SQL rather that string concatenation. Your code, as is, won't work is someone searches for "O'Mally". 

    Private Sub BtnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnSearch.Click
    If TBSearch.Text = "" Then
        MsgBox("Please enter keyword to search...", MsgBoxStyle.Information, "Keyword to search...")`
        TBSearch.Focus()
        Exit Sub
    End If
    Call OpenConnection()
    With OleDa
        Call Initialized()
        .SelectCommand = New OleDb.OleDbCommand() 
        .SelectCommand.CommandText = "SELECT * FROM [HighSchool] WHERE [LastName] Like @TBSearch or [FirstName] Like @TBSearch or [MI] Like @TBSearch Or [Gender] Like @TBSearch or [Address] Like @TBSearch or [Birthday] Like @TBSearch or [RNumber] Like @TBSearch Or [ENumber] Like @TBSearch ORDER By LastName ASC"
        .SelectCommand.Connection = OleCn
        .SelectCommand.Parameters.AddWithValue("@TBSearch", "%" & TBSearch.Text & "%")

        Call PopulateListView()

        If Me.LV.Items.Count >= 1 Then
            MsgBox(Me.LV.Items.Count & " Record(s) found for " & "( " & Me.TBSearch.Text & " )", MsgBoxStyle.OkOnly, "Record(s) found...")
        Else
            MsgBox("No record(s) found for " & "( " & Me.TBSearch.Text & " )" & " , please try again... ", MsgBoxStyle.Critical, "No record found...")
            TBSearch.Focus()
            TBSearch.SelectAll()
        End If
    End With
    Call CloseConnection()
End Sub

As for your error, the only possible cause is that OleDa is Nothing.

Upvotes: 2

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