vb.net - 在 vb.net 中调试？

Question

我是编码新手，我一直在使用 Visual Basic 开发我的在线计费系统项目。

已完成完整的编码，但在运行代码时，未计算 totalitems 和 totalamt。您能否调试或指导我如何解决此问题...

它显示错误，例如 1.conversion of type dbnull to string is not valid 2.string 或二进制数据将被截断。

Public Class billing

        Dim disAmount As Double
        Dim getProducID As Integer
        Dim getStocks As Integer
        Dim validatestock As Integer
        Dim getUnitPrice As Double
        Dim loadqty As Double
        Dim discount As Boolean
        Private Sub billing_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
            getTransactionID()
            GenerateInvoiceNo()
            fillComboproduct()
        End Sub
        Private Sub getTransactionID()
            Try
                Dim trans As New Random
                Dim numbers As Integer = trans.Next(1, 1000000)
                Dim digitss As String = numbers.ToString("000000")
                txttrans.Text = digitss
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try
        End Sub
        Private Sub GenerateInvoiceNo()
            lblInvoice.Text = "INV-" & GetUniqueKey(8)
        End Sub
        Public Shared Function GetUniqueKey(ByVal maxSize As Integer) As String
            Dim chars As Char() = New Char(61) {}
            chars = "123456789".ToCharArray()
            Dim data As Byte() = New Byte(0) {}
            Dim crypto As New RNGCryptoServiceProvider()
            crypto.GetNonZeroBytes(data)
            data = New Byte(maxSize - 1) {}
            crypto.GetNonZeroBytes(data)
            Dim result As New StringBuilder(maxSize)
            For Each b As Byte In data
                result.Append(chars(b Mod (chars.Length)))
            Next
            Return result.ToString()
        End Function
        Private Sub fillComboproduct()
            Dim query As String = "Select productname From product order by productname"
            Dim dtproduct As DataTable = getDataTable(query)

            txtproductame.DataSource = dtproduct
            txtproductame.DisplayMember = "productname"
            '   txtproductame.ValueMember = "productID"

            If txtproductame.Items.Count > 0 Then
                txtproductame.SelectedIndex = 0
            End If
        End Sub
        Private Sub clear()
            txtproductID.Text = ""
            txtprice.Text = ""
            txtQuantity.Text = ""
            txtBalance.Text = ""
            txttotal.Text = ""
            txtAmtPaid.Text = ""
            lblSubTotal.Text = "0"
            txtproductame.Text = ""
            lblTotalAmount.Text = "0.00"
            lblSubTotal.Text = "0.00"
            lblTotalItems.Text = "0"
            txtprice.Text = ""
            txtQuantity.Text = "1"
            txttotal.Text = "0.00"
        End Sub
        Private Sub addbills()
            Try
                Sql = "INSERT INTO bills VALUES( '" & txtproductID.Text & "', '" & txtproductame.Text & "','" & txtQuantity.Text & "', '" & txtprice.Text & "','" & txttotal.Text & "', '" & lblInvoice.Text & "', '" & Date.Today & "')"
                ConnDB()
            cmd = New SqlCommand(sqL, conn)
            Dim i As Integer
                i = cmd.ExecuteNonQuery
            Catch ex As Exception
                MsgBox(ex.Message)
            Finally
                cmd.Dispose()
                conn.Close()
            End Try
        End Sub
        Private Sub loadbills()
            Try
                Sql = "SELECT productID,productname,qty,unitprice FROM bills WHERE invoiceno = '" & Trim(lblInvoice.Text) & "' "
                ConnDB()
            cmd = New SqlCommand(sqL, conn)
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
                dgw.Rows.Clear()
                Do While dr.Read = True
                    dgw.Rows.Add(dr(0), dr(1), dr(2), dr(3))
                Loop
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try
        End Sub
        Private Sub totalamt()
            Try
                Sql = "SELECT sum(totalamt) FROM bills where invoiceno = '" & Trim(lblInvoice.Text) & "' "
                ConnDB()
            cmd = New SqlCommand(sqL, conn)
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
                Do While dr.Read = True
                    lblTotalAmount.Text = dr(0)
                Loop
            Catch ex As Exception
            End Try
        End Sub
        Private Sub gettotalitems()
        Try

            Sql = "SELECT sum(qty) FROM bills where invoiceno = '" & Trim(lblInvoice.Text) & "' "
            ConnDB()
            cmd = New SqlCommand(sqL, conn)
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
            Do While dr.Read = True
                lblTotalItems.Text = dr(0)
            Loop
        Catch ex As Exception
        End Try
        End Sub
        Private Sub saveitems()
            Try
                Sql = "INSERT INTO transactionDetails VALUES('" & txttrans.Text & "','" & lblInvoice.Text & "', '" & lblTotalItems.Text & "', '" & lblTotalAmount.Text & "', '" & txtAmtPaid.Text & "','" & txtBalance.Text & "', '" & cmdpayment.Text & "', '" & Date.Today & "')"
                ConnDB()
            cmd = New SqlCommand(sqL, conn)
            Dim i As Integer
                i = cmd.ExecuteNonQuery
                If i > 0 Then
                    MsgBox("Billing Details Successfully saved", MsgBoxStyle.Information, "Saves Billing Details")
                Else
                    MsgBox("Failed in Saves Billing Details", MsgBoxStyle.Information, "Saves Billing Details")
                End If
            Catch ex As Exception
                MsgBox(ex.Message)
            Finally
                cmd.Dispose()
                conn.Close()
            End Try
        End Sub
        Private Sub txtproductame_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtproductame.SelectedIndexChanged
            Try
                ConnDB()
            Dim da As New SqlDataAdapter(("select * from product where productname ='" & Trim(txtproductame.Text) & "'"), conn)
            Dim dt As New DataTable
                da.Fill(dt)
                If dt.Rows.Count > 0 Then
                    Me.txtprice.Text = dt.Rows(0).Item("unitprice") & ""
                    Me.txtproductID.Text = dt.Rows(0).Item("productID") & ""
                End If
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try
        End Sub
        Private Sub txtQuantity_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtQuantity.TextChanged
            txttotal.Text = Val(txtQuantity.Text) * Val(txtprice.Text)
        End Sub
        Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
            Me.Close()
        End Sub
        Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
            getTransactionID()
            GenerateInvoiceNo()
        End Sub
        Private Sub BindToText()
            Try
                With dgw
                lblSubTotal.Text = Val(.SelectedRows(0).Cells("qty").Value) * Val(.SelectedRows(0).Cells("price").Value)
                .SelectedRows(0).Cells("amt").Value = lblSubTotal.Text
            End With
            Catch ex As Exception
            End Try
        End Sub
        Private Sub dgw_CellClick(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgw.CellClick
            BindToText()
        End Sub
        Private Sub dgw_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles dgw.SelectionChanged
            BindToText()
        End Sub
        Private Sub txtAmtPaid_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtAmtPaid.KeyPress
            Dim ch As Char = e.KeyChar
            If Char.IsLetter(ch) Then   'Ristricting To Input Only Digits(any number)
                e.Handled = True
            End If
        End Sub
        Private Sub txtQuantity_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtQuantity.KeyPress
            Dim ch As Char = e.KeyChar
            If Char.IsLetter(ch) Then   'Ristricting To Input Only Digits(any number)
                e.Handled = True
            End If
        End Sub
        Private Sub btnload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnload.Click
            Try
                txttotal.Text = Val(txtprice.Text) * Val(txtQuantity.Text)
                If txtproductame.Text = "" Or txtQuantity.Text = "" Then
                    MsgBox("Please enter a product Or Quantity before you click load button")
                Else
                    addbills()
                    loadbills()
                    totalamt()
                    gettotalitems()
                End If
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try

            txttotal.Text = ""
            txtQuantity.Text = ""
        End Sub
        Private Sub btnsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsave.Click
            If dgw.Rows.Count = 0 Then
                MsgBox("Please load drugs in the cart before saving", MsgBoxStyle.Exclamation, "Validation")
                Exit Sub
            End If

            If txtAmtPaid.Text = "" Then
                MsgBox("Please fill-in Amount Paid by Customer", MsgBoxStyle.Information, "Validation")
                txtAmtPaid.Focus()
                Exit Sub
            ElseIf cmdpayment.Text = "" Then
                MsgBox("Please choose Payment status field", MsgBoxStyle.Information, "Validation")
                cmdpayment.Focus()
                Exit Sub
            End If
            saveitems()
            'DecreaseStocksOnhand()
            'UpdateToDecreaseStocksOnHand()
            btnreceipt.Show()
            getTransactionID()
            '  GenerateInvoiceNo()
            dgw.Rows.Clear()
            '    btnreceipt.Show()
        End Sub
        Private Sub Deleteitem()
            Try
                Sql = "DELETE * FROM bills WHERE productID = '" & dgw.SelectedRows(0).Cells("productID").Value & "'"
                ConnDB()
            cmd = New SqlCommand(sqL, conn)
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
                Do While dr.Read = True
                    dgw.Rows.Add(dr(0), dr(1), dr(2), dr(3))
                Loop
            Catch ex As Exception
                MsgBox(ex.Message)
            Finally
                cmd.Dispose()
                conn.Close()
            End Try
        End Sub
        Private Sub btnremove_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnremove.Click
            If MsgBox("Are you sure you want to remove this Product from Cart", MsgBoxStyle.YesNo, "Validation") = MsgBoxResult.Yes Then
                Deleteitem()
                loadbills()
                gettotalitems()
                totalamt()
                clear()
                txttotal.Text = ""
                txtQuantity.Text = ""
            End If
        End Sub
        Private Sub txtAmtPaid_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtAmtPaid.TextChanged
            txtBalance.Text = Val(lblTotalAmount.Text) - Val(txtAmtPaid.Text)
        End Sub
        Private Sub cmdpayment_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdpayment.SelectedIndexChanged
            If cmdpayment.SelectedIndex = 1 Then
                txtAmtPaid.Text = "0"
            End If
        End Sub
    Private Sub btnreceipt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnreceipt.Click
        receipt.lblInvoice.Text = lblInvoice.Text
        receipt.Show()
    End Sub
End Class

标签： vb.netdebugging