fails trying to save :unhandled exception of type "system.nullreferenceException.

  • Thread starter Thread starter Barret Bonden
  • Start date Start date
B

Barret Bonden

I get "An unhandled exception of type "system.nullreferenceException.
Object reference did not set to an instance of an object"
while trying to save back to the database - relating to : da.Update(ds)
, the last line of code in this listing. Just starting tyring to learn data
in vb.net- wanted to hand code data access from a form, and it all works
fine , but for saving back to the source.

Trying to learn ...

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

Public Class Form1
Inherits System.Windows.Forms.Form
Private recordsread As Long
Private strconnect As String
Private mytable As String
Private mydataset As DataSet
Public ds As New DataSet
Public ot As DataTable
Public mytab As String '2nd way
Public da As OleDb.OleDbDataAdapter

' Public objconn As OleDb.OleDbDataAdapter
' Dim objConn As New OleDb.OleDbConnection(con)



#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeComponent()

'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
Friend WithEvents btnnext As System.Windows.Forms.Button
Friend WithEvents Button1 As System.Windows.Forms.Button
Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
Friend WithEvents Button2 As System.Windows.Forms.Button
Friend WithEvents Button3 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.TextBox1 = New System.Windows.Forms.TextBox
Me.btnnext = New System.Windows.Forms.Button
Me.Button1 = New System.Windows.Forms.Button
Me.TextBox2 = New System.Windows.Forms.TextBox
Me.Button2 = New System.Windows.Forms.Button
Me.Button3 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point(72, 88)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.Size = New System.Drawing.Size(128, 20)
Me.TextBox1.TabIndex = 0
Me.TextBox1.Text = "TextBox1"
'
'btnnext
'
Me.btnnext.Location = New System.Drawing.Point(32, 168)
Me.btnnext.Name = "btnnext"
Me.btnnext.Size = New System.Drawing.Size(56, 24)
Me.btnnext.TabIndex = 1
Me.btnnext.Text = "next"
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(176, 160)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(48, 32)
Me.Button1.TabIndex = 2
Me.Button1.Text = "load "
'
'TextBox2
'
Me.TextBox2.Location = New System.Drawing.Point(72, 120)
Me.TextBox2.Name = "TextBox2"
Me.TextBox2.Size = New System.Drawing.Size(128, 20)
Me.TextBox2.TabIndex = 3
Me.TextBox2.Text = "TextBox2"
'
'Button2
'
Me.Button2.Location = New System.Drawing.Point(32, 208)
Me.Button2.Name = "Button2"
Me.Button2.Size = New System.Drawing.Size(56, 24)
Me.Button2.TabIndex = 4
Me.Button2.Text = "prior"
'
'Button3
'
Me.Button3.Location = New System.Drawing.Point(176, 208)
Me.Button3.Name = "Button3"
Me.Button3.Size = New System.Drawing.Size(48, 24)
Me.Button3.TabIndex = 5
Me.Button3.Text = "save "
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 266)
Me.Controls.Add(Me.Button3)
Me.Controls.Add(Me.Button2)
Me.Controls.Add(Me.TextBox2)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.btnnext)
Me.Controls.Add(Me.TextBox1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region



Private Sub btnnext_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnnext.Click
Me.BindingContext(ds, mytab).Position += 1

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim con As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data
Source=F:\old d\splash\SPLASH.MDB;Persist Security Info=False "
Dim sSQL As String
sSQL = "select * from company"
Dim objConn As New OleDb.OleDbConnection(con)
' objconn = New OleDb.OleDbConnection(con)
mytab = "company" '2nd way
Dim da As New OleDb.OleDbDataAdapter(sSQL, con)
' Dim ds As New DataSet("test")
' Dim ds As New DataSet
Dim dv As DataView

Try
objConn.Open()

Catch myexception As System.Exception
Windows.Forms.MessageBox.Show(myexception.Message)

End Try


If objConn.State = ConnectionState.Open Then
Try


' da.Fill(ds, "company")
da.Fill(ds, mytab)

objConn.Close()
' Dim ot As DataTable
ot = ds.Tables("company")

'dim dr as DataRow = ot.Rows.
'Dim dc As DataColumn
Dim s1 As Single
s1 = ot.Rows.Count
Dim dr As DataRow
For Each dr In ds.Tables("company").Rows
' TextBox3.Text = dr("company")
' ComboBox1.Items.Add(dr("company"))
Console.WriteLine(dr("company"))
Next
s1 = ot.Columns.Count
' TextBox2.Text = s1
dv = ot.DefaultView
setcontbind()


TextBox1.DataBindings.Add("text", dv, "company")

Catch myexception As System.Exception
Windows.Forms.MessageBox.Show(myexception.Message)

End Try
End If
End Sub
Private Sub setcontbind()
TextBox2.DataBindings.Add("text", ds, "company.company")
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button2.Click
Me.BindingContext(ds, mytab).Position -= 1
End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button3.Click
da.Update(ds)
End Sub
End Class
 
Hi Barret,


In Button3_Click event you try to use global da to update
ds. But the global da is never initialized.

Although in Button1_Click you use following code
Dim da As New OleDb.OleDbDataAdapter(sSQL, con)

It actually creates another da, a local da in
Button1_Click.

Change it to
da = New OleDb.OleDbDataAdapter(sSQL, con)
No 'Dim'! No 'As'!

HTH

Elton Wang
(e-mail address removed)
-----Original Message-----
I get "An unhandled exception of
Click to expand...
type "system.nullreferenceException.
Object reference did not set to an instance of an object"
while trying to save back to the database - relating to : da.Update(ds)
, the last line of code in this listing. Just starting tyring to learn data
in vb.net- wanted to hand code data access from a form, and it all works
fine , but for saving back to the source.

Trying to learn ...

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

Public Class Form1
Inherits System.Windows.Forms.Form
Private recordsread As Long
Private strconnect As String
Private mytable As String
Private mydataset As DataSet
Public ds As New DataSet
Public ot As DataTable
Public mytab As String '2nd way
Public da As OleDb.OleDbDataAdapter

' Public objconn As OleDb.OleDbDataAdapter
' Dim objConn As New OleDb.OleDbConnection(con)



#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeComponent()

'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
Friend WithEvents btnnext As System.Windows.Forms.Button
Friend WithEvents Button1 As System.Windows.Forms.Button
Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
Friend WithEvents Button2 As System.Windows.Forms.Button
Friend WithEvents Button3 As System.Windows.Forms.Button
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
Me.TextBox1 = New System.Windows.Forms.TextBox
Me.btnnext = New System.Windows.Forms.Button
Me.Button1 = New System.Windows.Forms.Button
Me.TextBox2 = New System.Windows.Forms.TextBox
Me.Button2 = New System.Windows.Forms.Button
Me.Button3 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point (72, 88)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.Size = New System.Drawing.Size(128, 20)
Me.TextBox1.TabIndex = 0
Me.TextBox1.Text = "TextBox1"
'
'btnnext
'
Me.btnnext.Location = New System.Drawing.Point (32, 168)
Me.btnnext.Name = "btnnext"
Me.btnnext.Size = New System.Drawing.Size(56, 24)
Me.btnnext.TabIndex = 1
Me.btnnext.Text = "next"
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point (176, 160)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(48, 32)
Me.Button1.TabIndex = 2
Me.Button1.Text = "load "
'
'TextBox2
'
Me.TextBox2.Location = New System.Drawing.Point (72, 120)
Me.TextBox2.Name = "TextBox2"
Me.TextBox2.Size = New System.Drawing.Size(128, 20)
Me.TextBox2.TabIndex = 3
Me.TextBox2.Text = "TextBox2"
'
'Button2
'
Me.Button2.Location = New System.Drawing.Point (32, 208)
Me.Button2.Name = "Button2"
Me.Button2.Size = New System.Drawing.Size(56, 24)
Me.Button2.TabIndex = 4
Me.Button2.Text = "prior"
'
'Button3
'
Me.Button3.Location = New System.Drawing.Point (176, 208)
Me.Button3.Name = "Button3"
Me.Button3.Size = New System.Drawing.Size(48, 24)
Me.Button3.TabIndex = 5
Me.Button3.Text = "save "
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 266)
Me.Controls.Add(Me.Button3)
Me.Controls.Add(Me.Button2)
Me.Controls.Add(Me.TextBox2)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.btnnext)
Me.Controls.Add(Me.TextBox1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region



Private Sub btnnext_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnnext.Click
Me.BindingContext(ds, mytab).Position += 1

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim con As String
Click to expand...
= "Provider=Microsoft.Jet.OLEDB.4.0; Data
 
got it ! very kind of you ... bit by vb.net again ; I'll learn .....( I
miss vb 6; *sigh* ...)
 
a new error now:
"An unhandled exception of type 'System.InvalidOperationException' occurred
in system.data.dll

Additional information: Update unable to find TableMapping['Table'] or
DataTable 'Table'."

I substituted your line of code and got that as I tried to update - totally
lost on this one ..


Imports System

Imports System.Data

Imports System.Data.OleDb

Public Class Form1

Inherits System.Windows.Forms.Form

Private recordsread As Long

Private strconnect As String

Private mytable As String

Private mydataset As DataSet

Public ds As New DataSet

Public ot As DataTable

Public mytab As String '2nd way

Public da As OleDb.OleDbDataAdapter

' Public objconn As OleDb.OleDbDataAdapter

' Dim objConn As New OleDb.OleDbConnection(con)





#Region " Windows Form Designer generated code "

Public Sub New()

MyBase.New()

'This call is required by the Windows Form Designer.

InitializeComponent()

'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.

Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

If disposing Then

If Not (components Is Nothing) Then

components.Dispose()

End If

End If

MyBase.Dispose(disposing)

End Sub

'Required by the Windows Form Designer

Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer

'It can be modified using the Windows Form Designer.

'Do not modify it using the code editor.

Friend WithEvents TextBox1 As System.Windows.Forms.TextBox

Friend WithEvents btnnext As System.Windows.Forms.Button

Friend WithEvents Button1 As System.Windows.Forms.Button

Friend WithEvents TextBox2 As System.Windows.Forms.TextBox

Friend WithEvents Button2 As System.Windows.Forms.Button

Friend WithEvents Button3 As System.Windows.Forms.Button

<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

Me.TextBox1 = New System.Windows.Forms.TextBox

Me.btnnext = New System.Windows.Forms.Button

Me.Button1 = New System.Windows.Forms.Button

Me.TextBox2 = New System.Windows.Forms.TextBox

Me.Button2 = New System.Windows.Forms.Button

Me.Button3 = New System.Windows.Forms.Button

Me.SuspendLayout()

'

'TextBox1

'

Me.TextBox1.Location = New System.Drawing.Point(72, 88)

Me.TextBox1.Name = "TextBox1"

Me.TextBox1.Size = New System.Drawing.Size(128, 20)

Me.TextBox1.TabIndex = 0

Me.TextBox1.Text = "TextBox1"

'

'btnnext

'

Me.btnnext.Location = New System.Drawing.Point(32, 168)

Me.btnnext.Name = "btnnext"

Me.btnnext.Size = New System.Drawing.Size(56, 24)

Me.btnnext.TabIndex = 1

Me.btnnext.Text = "next"

'

'Button1

'

Me.Button1.Location = New System.Drawing.Point(176, 160)

Me.Button1.Name = "Button1"

Me.Button1.Size = New System.Drawing.Size(48, 32)

Me.Button1.TabIndex = 2

Me.Button1.Text = "load "

'

'TextBox2

'

Me.TextBox2.Location = New System.Drawing.Point(72, 120)

Me.TextBox2.Name = "TextBox2"

Me.TextBox2.Size = New System.Drawing.Size(128, 20)

Me.TextBox2.TabIndex = 3

Me.TextBox2.Text = "TextBox2"

'

'Button2

'

Me.Button2.Location = New System.Drawing.Point(32, 208)

Me.Button2.Name = "Button2"

Me.Button2.Size = New System.Drawing.Size(56, 24)

Me.Button2.TabIndex = 4

Me.Button2.Text = "prior"

'

'Button3

'

Me.Button3.Location = New System.Drawing.Point(176, 208)

Me.Button3.Name = "Button3"

Me.Button3.Size = New System.Drawing.Size(48, 24)

Me.Button3.TabIndex = 5

Me.Button3.Text = "save "

'

'Form1

'

Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)

Me.ClientSize = New System.Drawing.Size(292, 266)

Me.Controls.Add(Me.Button3)

Me.Controls.Add(Me.Button2)

Me.Controls.Add(Me.TextBox2)

Me.Controls.Add(Me.Button1)

Me.Controls.Add(Me.btnnext)

Me.Controls.Add(Me.TextBox1)

Me.Name = "Form1"

Me.Text = "Form1"

Me.ResumeLayout(False)

End Sub

#End Region


Private Sub btnnext_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnnext.Click

Me.BindingContext(ds, mytab).Position += 1

End Sub

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

Dim con As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=F:\old
d\splash\SPLASH.MDB;Persist Security Info=False "

Dim sSQL As String

sSQL = "select * from company"

Dim objConn As New OleDb.OleDbConnection(con)

' objconn = New OleDb.OleDbConnection(con)

mytab = "company" '2nd way

' Dim da As New OleDb.OleDbDataAdapter(sSQL, con)

da = New OleDb.OleDbDataAdapter(sSQL, con)

' Dim ds As New DataSet("test")

' Dim ds As New DataSet

Dim dv As DataView

Try

objConn.Open()

Catch myexception As System.Exception

Windows.Forms.MessageBox.Show(myexception.Message)

End Try



If objConn.State = ConnectionState.Open Then

Try



' da.Fill(ds, "company")

da.Fill(ds, mytab)

objConn.Close()

' Dim ot As DataTable

ot = ds.Tables("company")

'dim dr as DataRow = ot.Rows.

'Dim dc As DataColumn

Dim s1 As Single

s1 = ot.Rows.Count

Dim dr As DataRow

For Each dr In ds.Tables("company").Rows

' TextBox3.Text = dr("company")

' ComboBox1.Items.Add(dr("company"))

Console.WriteLine(dr("company"))

Next

s1 = ot.Columns.Count

' TextBox2.Text = s1

dv = ot.DefaultView

setcontbind()



TextBox1.DataBindings.Add("text", dv, "company")

Catch myexception As System.Exception

Windows.Forms.MessageBox.Show(myexception.Message)

End Try

End If

End Sub

Private Sub setcontbind()

TextBox2.DataBindings.Add("text", ds, "company.company")

End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button2.Click

Me.BindingContext(ds, mytab).Position -= 1

End Sub

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button3.Click

da.Update(ds)

'lash_control()

End Sub

End Class
 
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