输入字符串格式不正确（计算器）

Question

好的，所以我创建了一个计算千瓦成本的程序，每当我选择3个设备中的2个时，我收到此错误消息

  

未处理的类型＆＃39; System.FormatException＆＃39;发生在mscorlib.dll中   附加信息：输入字符串的格式不正确。

这是完整的代码，我不知道哪里出错了。请帮忙？

Public Class Form1

    Private RunningTotal As Double




    Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click
        Dim kw As Double = Convert.ToDouble(txtKW.Text)
        Dim hpd As Double = Convert.ToDouble(txtHPD.Text)
        Dim kwpd As Double = Convert.ToDouble(txtKWPH.Text)
        Dim gal As Double = Convert.ToDouble(txtGallon.Text)
        Dim cpg As Double = Convert.ToDouble(txtCostPerGal.Text)
        Dim result As Double = kw * hpd * kwpd * gal * cpg
        lblResults.Text = result.ToString("C")
        RunningTotal = RunningTotal + result
        lblRunning.Text = RunningTotal.ToString("C")


        kw = Convert.ToDouble(txtKW.Text)
        hpd = Convert.ToDouble(txtHPD.Text)
        kwpd = Convert.ToDouble(txtKWPH.Text)
        gal = Convert.ToDouble(txtGallon.Text)
        cpg = Convert.ToDouble(txtCostPerGal.Text)








    End Sub

    Private Sub QuitToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles QuitToolStripMenuItem.Click
        Close()
    End Sub

    Private Sub AboutToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles AboutToolStripMenuItem.Click
        MessageBox.Show("This program was made by BD")
    End Sub

    Private Sub txtKW_TextChanged(sender As Object, e As EventArgs) Handles txtKW.TextChanged
        If IsNumeric(txtKW.Text) = True Then
            If (txtKW.Text = "0123456789") Then
                lblResults.Text = DialogResult.ToString("c")
            End If

        Else
            MessageBox.Show("Please enter a number")
        End If

    End Sub

    Private Sub txtHPD_TextChanged(sender As Object, e As EventArgs) Handles txtHPD.TextChanged
        If IsNumeric(txtHPD.Text) = True Then
            If (txtHPD.Text = "0123456789") Then
                lblResults.Text = DialogResult.ToString("c")
            End If

        Else
            MessageBox.Show("Please enter a number")
        End If
    End Sub

    Private Sub txtKWPH_TextChanged(sender As Object, e As EventArgs) Handles txtKWPH.TextChanged
        If IsNumeric(txtKWPH.Text) = True Then
            If (txtKWPH.Text = "0123456789") Then
                lblResults.Text = DialogResult.ToString("c")
            End If

        Else
            MessageBox.Show("Please enter a number")
        End If
    End Sub

    Private Sub HelpToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles HelpToolStripMenuItem.Click
        MessageBox.Show("This program was designed to help you determine your cost of appliances, simply enter the amount of kilowatts your appliance uses, how many hours per day you use your appliance, and the cost per kilowatt hour then click calculate.")
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim index As Integer = ComboBox1.SelectedIndex
        If (index = 2) Then
            txtGallon.Visible = True
            txtCostPerGal.Visible = True

        Else
            txtGallon.Visible = False
            txtCostPerGal.Visible = False
        End If


    End Sub

    Private Sub Label2_Click(sender As Object, e As EventArgs) Handles lblGallons.Click

    End Sub

    Private Sub txtGallon_TextChanged(sender As Object, e As EventArgs) Handles txtGallon.TextChanged
        If IsNumeric(txtGallon.Text) = True Then
            If (txtGallon.Text = "0123456789") Then
                lblResults.Text = DialogResult.ToString("c")
            End If

        Else
            MessageBox.Show("Please enter a number")

        End If

    End Sub



    Private Sub txtCostPerGal_TextChanged(sender As Object, e As EventArgs) Handles txtCostPerGal.TextChanged
        If IsNumeric(txtCostPerGal.Text) = True Then
            If (txtCostPerGal.Text = "0123456789") Then
                lblResults.Text = DialogResult.ToString("c")
            End If

        Else
            MessageBox.Show("Please enter a number")

        End If

    End Sub

    Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged

    End Sub
End Class