Conversion of string " to integer type is not valid

Question

I am creating a simple program that records the total sales and the value already earned with sales, however, after the user put the sale value the error program.

The error is as follows:

Conversion of string " to integer type is not valid

Before it was working right, however only had 1 IF, now I have in total 10 IF, which register according to the number of sales the value in different variables, the code in question:

Public Class addvenda
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles boxvenda.TextChanged

End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If My.Settings.numerovendas = 0 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda1 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 1 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda2 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 2 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda3 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 3 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda4 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 4 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda5 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 5 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda6 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 6 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda7 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 7 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda8 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 8 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda9 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If
    If My.Settings.numerovendas = 9 Then
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.venda10 = boxvenda.Text
        My.Settings.totalvendas += boxvenda.Text
        Me.Close()
    End If

End Sub

Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick

End Sub

End Class

Answer 1

The error must be happening because the text that is in boxvenda.Text is empty and cannot be converted to a valid number.

I think this way you can avoid the error, and at the same time greatly optimize your code:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim dblBoxVenda As Double = 0

    If My.Settings.numerovendas >= 0 And My.Settings.numerovendas <= 9 Then
        'Converter o valor da TextBox para Double, caso seja possível
        'Se não for possível, o valor é "0"
        Double.TryParse(boxvenda.Text, dblBoxVenda)

        'Pegar no setting correspondente
        My.Settings.Item(String.Format("venda{0}", My.Settings.numerovendas + 1)) = dblBoxVenda
        My.Settings.vendas += 1
        My.Settings.numerovendas += 1
        My.Settings.totalvendas += dblBoxVenda
        My.Settings.Save()

        Close()
    End If
End Sub

Remember to mention the My.Settings.Save(), otherwise the changes will not be saved in the click button.