VB 10 Save Button Click

[vivekmonteiro2004]

Hi I am new to VB,

When I click Save button my error goes to below line saying nullvalue.

Is it belolw line is right code to update value to MS access tables from datagrid.


Myadpt.Update(Dataset.Tables(0))

Regards

[jmcilhinney]

That means that either 'Myadpt' is Nothing or 'Dataset' is Nothing. Please show us the entire method that contains that line of code and also the code where you think those two objects were created.

[vivekmonteiro2004]

Below is the entire code.

Imports System.Data.OleDb
Public Class Form1

    Dim Myconnection As OleDbConnection
    Dim Myadpt As OleDbDataAdapter
    Dim CMDbuilder As OleDbCommandBuilder
    Dim Dataset As New DataSet
    Dim mytable As New DataTable
    Dim fname As String
    Dim lname As String
    Dim phonenumber As String
    Dim mobilenumber As String
    Dim emailaddress As String
    Dim Maxrows As Integer


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

        btnsave.Visible = (False)
        Try
            Myconnection = New OleDbConnection
            Myconnection.ConnectionString = "Provider=Microsoft.Ace.Oledb.12.0;Data source = C:\Contact\Contact\contact.accdb"

            Myconnection.Open()
            Dim Myadpt As OleDbDataAdapter = New OleDbDataAdapter(String.Format("select * from contact"), Myconnection)
            CMDbuilder = New OleDbCommandBuilder(Myadpt)
            Myadpt.Fill(Dataset, "Contact")
            '--------
            Maxrows = Dataset.Tables("Contact").Rows.Count
            '---------------

            Contactview.DataSource = Dataset.Tables("contact")
            Contactview.Refresh()
            Contactview.AllowUserToAddRows = False
            Contactview.ReadOnly = True

        Catch ex As Exception

            MsgBox("Error")

        End Try

    End Sub

    Private Sub Btnadd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnadd.Click

        For Each txt In gbox.Controls
            If TypeOf txt Is TextBox Then txt.enabled = True

        Next

        btnsave.Visible = (True)

    End Sub

    Private Sub btnclose_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnclose.Click
        Me.Close()
    End Sub

    Private Sub btnsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsave.Click
        Dim newrow As DataRow
        For Each datarow In Contactview.Rows
            datarow.selected = False

        Next
        Maxrows = Dataset.Tables(0).Rows.Count

        fname = txtfname.Text
        lname = txtlname.Text
        phonenumber = txtphonenumber.Text
        mobilenumber = txtmobilenumber.Text
        emailaddress = txtemailaddress.Text

        newrow = Dataset.Tables(0).NewRow()

        newrow.Item(0) = Maxrows
        newrow.Item(1) = fname
        newrow.Item(2) = lname
        newrow.Item(3) = phonenumber
        newrow.Item(4) = mobilenumber
        newrow.Item(5) = emailaddress
        Dataset.Tables("contact").Rows.Add(newrow)


        Myadpt.Update(Dataset.Tables("contact"))
        Contactview.DataSource = Dataset.Tables("contact")
        Contactview.Refresh()
        Contactview.Rows(Maxrows).Selected = True

        For Each txt In gbox.Controls
            If TypeOf txt Is TextBox Then txt.enabled = False


        Next

        btnsave.Visible = (False)

        txtfname.Text = ""
        txtlname.Text = ""
        txtphonenumber.Text = ""
        txtmobilenumber.Text = ""
        txtemailaddress.Text = ""

        
        Maxrows += 1
    End Sub

End Class

[jmcilhinney]

I didn't ask for the entire code. I asked for the code that was relevant to the problem. If you expect us to wade through code to focus on what's relevant so you don't have to, you're likely to find people becoming less enthused about helping.

Also, please use formatting tags when posting code for readability.

Imports System.Data.OleDb
Public Class Form1
 
    Dim Myconnection As OleDbConnection
    Dim Myadpt As OleDbDataAdapter
    Dim CMDbuilder As OleDbCommandBuilder
    Dim Dataset As New DataSet
    Dim mytable As New DataTable
    Dim fname As String
    Dim lname As String
    Dim phonenumber As String
    Dim mobilenumber As String
    Dim emailaddress As String
    Dim Maxrows As Integer
 
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
        btnsave.Visible = (False)
        Try
            Myconnection = New OleDbConnection
            Myconnection.ConnectionString = "Provider=Microsoft.Ace.Oledb.12.0;Data source = C:\Contact\Contact\contact.accdb"
 
            Myconnection.Open()
            Dim Myadpt As OleDbDataAdapter = New OleDbDataAdapter(String.Format("select * from contact"), Myconnection)
            CMDbuilder = New OleDbCommandBuilder(Myadpt)
            Myadpt.Fill(Dataset, "Contact")
            '--------
            Maxrows = Dataset.Tables("Contact").Rows.Count
            '---------------
 
            Contactview.DataSource = Dataset.Tables("contact")
            Contactview.Refresh()
            Contactview.AllowUserToAddRows = False
            Contactview.ReadOnly = True
 
        Catch ex As Exception
 
            MsgBox("Error")
 
        End Try
 
    End Sub
 
    Private Sub Btnadd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnadd.Click
 
        For Each txt In gbox.Controls
            If TypeOf txt Is TextBox Then txt.enabled = True
 
        Next
 
        btnsave.Visible = (True)
 
    End Sub
 
    Private Sub btnclose_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnclose.Click
        Me.Close()
    End Sub
 
    Private Sub btnsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsave.Click
        Dim newrow As DataRow
        For Each datarow In Contactview.Rows
            datarow.selected = False
 
        Next
        Maxrows = Dataset.Tables(0).Rows.Count
 
        fname = txtfname.Text
        lname = txtlname.Text
        phonenumber = txtphonenumber.Text
        mobilenumber = txtmobilenumber.Text
        emailaddress = txtemailaddress.Text
 
        newrow = Dataset.Tables(0).NewRow()
 
        newrow.Item(0) = Maxrows
        newrow.Item(1) = fname
        newrow.Item(2) = lname
        newrow.Item(3) = phonenumber
        newrow.Item(4) = mobilenumber
        newrow.Item(5) = emailaddress
        Dataset.Tables("contact").Rows.Add(newrow)
 
 
        Myadpt.Update(Dataset.Tables("contact"))
        Contactview.DataSource = Dataset.Tables("contact")
        Contactview.Refresh()
        Contactview.Rows(Maxrows).Selected = True
 
        For Each txt In gbox.Controls
            If TypeOf txt Is TextBox Then txt.enabled = False
 
 
        Next
 
        btnsave.Visible = (False)
 
        txtfname.Text = ""
        txtlname.Text = ""
        txtphonenumber.Text = ""
        txtmobilenumber.Text = ""
        txtemailaddress.Text = ""
 
        
        Maxrows += 1
    End Sub
 
End Class

[jmcilhinney]

The issue is that you have two variables named 'Myadpt'. You declare one at the class level:

Dim Myadpt As OleDbDataAdapter

You then declare another at the method level in the Load event handler:

Dim Myadpt As OleDbDataAdapter = New OleDbDataAdapter(String.Format("select * from contact"), Myconnection)

It's that local variable that you assign an object to and use to retrieve the data, but that variable ceases to exist when the Load event handler completes and so that object becomes inaccessible. Later on, in the Click event handler of your save Button, you try to use the class-level variable to save the changes but you never assigned an object to that variable. As a result, that variable is Nothing, just as I said earlier.

The solution is to not declare that second variable at the method level. You don't do that for 'Myconnection' or 'Dataset' so there's no reason to do it for 'Myadpt' either.

On an unrelated note, I would suggest that you be a bit more consistent with your naming. If you have a variable named 'Myconnection' then why use 'Myadpt' rather than 'Myadapter' and why use 'Dataset' instead of 'Mydataset'? Personally, I would do away with the "My" prefix altogether. For those variables, I would tend to use 'connection', 'adapter' and 'data' but whatever you choose to go with, try to be consistent. Don't use abbreviations in some places and not others for no apparent reason and don't use prefixes in some places and not others either.

[vivekmonteiro2004]

Sorry for sending entire code which made others to consume time. Now I will study your second reply. Thank you.

[jmcilhinney]

The problem with too much code is that it can end up hiding the issue. It's not always easy to determine what is relevant but I did specify what to post on this occasion. The easier you can make it for us to help, the more likely we will be inclined and able to help, so the better for you.

[vivekmonteiro2004]

Thank you so much I changed code in method level and working fine.

adapter = New OleDbDataAdapter(String.Format("select * from contact"), connection)

[Shaggy Hiker]

I edited your post to add [CODE][/CODE] tags. You can do this by pressing the # button and pasting the code between the tags. To use the code formatting that JMC used in post #4, use the VB button (which looks like VE on many browsers).