pls help..iv juz started learning vb.net..encountered this problem in this code:
Private Sub NavigateRecords()
TextBox1.Text = ds.Tables("stdDataSet").Rows(inc).Item(0)-error msg appeared here sayin null reference evception was unhandled. Object reference not set to an instance of an object.
TextBox2.Text = ds.Tables("stdDataSet").Rows(inc).Item(1)
TextBox3.Text = ds.Tables("stdDataSet").Rows(inc).Item(2)
TextBox4.Text = ds.Tables("stdDataSet").Rows(inc).Item(3)
this is the full coding:
Public Class Form1
Dim con As New OleDb.OleDbConnection
Dim dbProvider As String
Dim dbSource As String
Dim sql As String
Dim da As OleDb.OleDbDataAdapter
Dim ds As New DataSet
Dim inc As Integer
Dim MaxRows As Integer
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
dbProvider = "Provider=Microsoft.ACE.OLEDB.12.0;"
dbSource = "Data Source = std.accdb"
con.ConnectionString = dbProvider & dbSource
con.Open()
sql = "SELECT * FROM Table1"
da = New OleDb.OleDbDataAdapter(sql, con)
da.Fill(ds, "stdDataSet")
MsgBox("Database is now open")
inc = -1
MaxRows = ds.Tables("stdDataSet").Rows.Count
con.Close()
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If inc <> MaxRows - 1 Then
inc = inc + 1
NavigateRecords()
Else
MsgBox("No more Rows")
End If
End Sub
Private Sub NavigateRecords()
TextBox1.Text = ds.Tables("stdDataSet").Rows(inc).Item(0)
TextBox2.Text = ds.Tables("stdDataSet").Rows(inc).Item(1)
TextBox3.Text = ds.Tables("stdDataSet").Rows(inc).Item(2)
TextBox4.Text = ds.Tables("stdDataSet").Rows(inc).Item(3)
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
If inc > 0 Then
inc = inc - 1
NavigateRecords()
Else
MsgBox("First Record")
End If
End Sub
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
If inc <> -1 Then
Dim cb As New OleDb.OleDbCommandBuilder(da)
Dim dsNewRow As DataRow
dsNewRow = ds.Tables("stdDataSet").NewRow()
dsNewRow.Item("Studentname") = TextBox1.Text
dsNewRow.Item("School") = TextBox2.Text
dsNewRow.Item("Age") = TextBox3.Text
dsNewRow.Item("Grade") = TextBox4.Text
ds.Tables("stdDataSet").Rows.Add(dsNewRow)
da.Update(ds, "stdDataSet")
MsgBox("New Record added to the Database")
Button1.Enabled = True
Button2.Enabled = True
End If
MaxRows = ds.Tables("stdDataSet").Rows.Count
inc = 0
NavigateRecords()
End Sub
Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
TextBox1.Text = ("")
TextBox2.Text = ("")
TextBox3.Text = ("")
TextBox4.Text = ("")
End Sub
Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
Dim cb As New OleDb.OleDbCommandBuilder(da)
ds.Tables("stdDataSet").Rows(inc).Item(0) = TextBox1.Text
ds.Tables("stdDataSet").Rows(inc).Item(1) = TextBox2.Text
ds.Tables("stdDataSet").Rows(inc).Item(2) = TextBox3.Text
ds.Tables("stdDataSet").Rows(inc).Item(3) = TextBox4.Text
da.Update(ds, "stdDataSet")
MsgBox("Data updated")
End Sub
Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
Dim cb As New OleDb.OleDbCommandBuilder(da)
If MessageBox.Show("Do you really want to Delete this Record?", _
"Delete", MessageBoxButtons.YesNo, _
MessageBoxIcon.Warning) = DialogResult.No Then
MsgBox("Operation Cancelled")
Exit Sub
End If
ds.Tables("stdDataSet").Rows(inc).Delete()
MaxRows = MaxRows - 1
da.Update(ds, "stdDataSet")
inc = 0
NavigateRecords()
End Sub
Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
If TextBox1.Text = "Adam" Then
inc = 0
ElseIf TextBox1.Text = "Ahmad" Then
inc = 1
ElseIf TextBox1.Text = "Sofia" Then
inc = 2
ElseIf TextBox1.Text = "Sarah" Then
inc = 3
End If
NavigateRecords()
End Sub
End Classpls help..:(
