saving data

i have a small program which calculates weights
but i want to store those weights into database
so i have one table in database and it has two fields FWeight and SWeight
there is button which calculates weights and i want that as i press it it should calculate and store first weight
secondly i have added a combo box to the form
i want that as i save first weight it should updated and i can select stored value from it and then it can display those value against first weight text box
code for save method

Code:

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Public Sub save()
        Try

            conn.Open()

            'command.Connection = conn
            Dim sql As String = String.Empty
            sql = "INSERT INTO Weight(FWeight,SWeight)Values(?,?,)"
            Dim command As New OleDbCommand(sql, conn)
            command.Parameters.AddWithValue("FWeight", txtFWeight.Text)
            command.Parameters.AddWithValue("SWeight", txtSWeight.Text)
            command.ExecuteNonQuery()

        Catch ex As Exception
            ' MsgBox(ex.ToString)

 Finally
            conn.Close()

        End Try
    End Sub

---

code for calculating total

Code:

---

Private Sub btnTotal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTotal.Click
        Try
            FWeight = CLng(txtFWeight.Text)
            SWeight = CLng(txtSWeight.Text)
            total = FWeight - SWeight
            txtTotal.Text = total & " Kg"
            totalMon = total / 40
            txtTotalMon.Text = totalMon
            save()
            Fill_FCombo()
        Catch ex As Exception
            MessageBox.Show("Values are too large", "Weight Calculator", MessageBoxButtons.OK, MessageBoxIcon.Information)
        End Try
    End Sub

---

code for cmbo box operations

Code:

---

Private Sub Fill_FCombo()
        Try
            Dim r As DataRow
            cmboFWeight.Items.Clear()
            For Each r In dSet.Tables(0).Rows
                cmboFWeight.Items.Add(r.Item(1))
            Next
        Catch ex As Exception

        End Try
    End Sub

    Private Sub cmboFWeight_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmboFWeight.SelectedIndexChanged
        Try
            dSet.Tables(0).PrimaryKey = New DataColumn() {dSet.Tables(0).Columns("FWeight")}
            Dim row As DataRow
            row = dSet.Tables(0).Rows.Find(cmboFWeight.Text)
            txtFWeight.Text = row("FWeight")
            txtSWeight.Text = row("SWeight")
        Catch ex As Exception

        End Try
    End Sub

---

Is there a question in there somewhere?????

problem of saving a record into table has been solved
but as i click btnTotal then record is saved in database but also i want that cmboFWeight should be updated and filled with all records
so i did it as follow

Code:

---

Private Sub Fill_FCombo()
        Try
            Dim r As DataRow
            cmboFWeight.Items.Clear()
            For Each r In dSet.Tables(0).Rows
                cmboFWeight.Items.Add(r.Item(1))
            Next
        Catch ex As Exception
            MsgBox(ex.ToString())
        End Try
    End Sub

---

but this gives exception "System.NullReferenceException:object instance not set to an instance of an object

so i also want that i can select a value from combo box and these values should be set into textboxes
so i did it as follow

Code:

---

  Private Sub cmboFWeight_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmboFWeight.SelectedIndexChanged
        Try
            dSet.Tables(0).PrimaryKey = New DataColumn() {dSet.Tables(0).Columns("FWeight")}
            Dim row As DataRow
            row = dSet.Tables(0).Rows.Find(cmboFWeight.Text)
            txtFWeight.Text = row("FWeight")
            txtSWeight.Text = row("SWeight")
        Catch ex As Exception

        End Try
    End Sub

---

kindly tell me the solution.