Acess dataset between 2 Windows Form

[fung1223]

Dear all
If I have 2 form, 1 call form1 and the other call form2.
I create a connection in form1:


CLASS FORM1
PUBLIC DS As DATASET

Dim connstr As String = "DSN=TEST"
Dim cn As New OdbcConnection(connstr)
Dim DA1 As New OdbcDataAdapter("SELECT * FROM A ", cn)

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

cn.Open()
odbcadapter1.Fill(DS, "A")

I can successfully access DS in form1, but when I try to access DS in form2, it said" object reference not set to instance of object". It seem that it treat it as a new variable. I try this in form2:

Dim zds As DataSet

zds = form1.ds
messagebox.show(zds.tables("A").Rows.count)

But still not work. Anyone can told me how to access it from anothe table? Thank you very much.

[DevGrp]

Just pass the dataset to Form2.

[fung1223]

Thank you for your reply.
But How?
Thank you

[dynamic_sysop]

in Form1 :

Public ds As New DataSet()
'/// make a public reference to ds ^^^
'///////////////////////////////////////////////
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim frm2 As New Form2()
    AddOwnedForm(frm2) '/// add it as owned by this form.
    frm2.Show()
End Sub

in Form2 :

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim frmMain As Form1 = Owner
    Dim zds As DataSet = frmMain.ds
    MessageBox.Show(zds.DataSetName)
End Sub

[fung1223]

Thank you for your reply. I have one question. Once I declar a public variable :

public ds as new dataset()

it doesnot mean I can access it everywhere? Or I can just access the variable, but not the value of the ds.....I quite confuse.
Now, It seem that I can use ds in form2 but I can not access the "value" in form2.

Another one told me a method is declare the dataset in a modules. What is the differece between declare a varibale as public and declare it in a modules. As I know, it looks like equal since both method can access the variable everywhere. Sorry for my long question. Sorry and Thank you for your help.

[dynamic_sysop]

here's a quick example , using oledb to open an access app
in Form1 :

Imports System.Data
 
Public ds As New DataSet()
Private frm2 As New Form2()
 
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    AddOwnedForm(frm2)
    frm2.Show()
 
End Sub

in Form2 :

Imports System.Data.OleDb
 
    Private frmMain As Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim constring As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\MyDb.mdb"
        frmMain = Owner '/// owner form.
 
        OpenAccess(constring)
    End Sub
 
    Public Function OpenAccess(ByVal strConnection As String, Optional ByVal strCommand As String = "SELECT * FROM Table1")
        Dim objCon As New OleDbConnection(strConnection)
        Try
            objCon.Open()
            Dim objCom As New OleDbCommand(strCommand, objCon)
            Dim objAdapt As New OleDbDataAdapter(objCom)
 
            objAdapt.Fill(frmMain.ds, "Table1")
            DataGrid1.DataSource = frmMain.ds.Tables("Table1")
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        Finally
            objCon.Close()
        End Try
 
    End Function