Debugging in vb.net? - vb.net

Question

I'm new to coding, I've been working on my project of online billing system using Visual Basic.
The complete coding has been done, but while running the code, the totalitems and totalamt is not being calculated. Can you please debug or guide me how can I resolve this issue...
It shows errors like
1.conversion of type dbnull to string is not valid
2.string or binary data would be truncated.
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