vb.net - エラーは「Conversion from string "" to type 'Double' is not valid」です

Question

Private Sub btntambah_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btntambah.Click
    Dim n As Integer
    For n = 0 To lv1.Items.Count - 1
        If lv1.Items(n).Text = txtkdbrng.Text Then
            MsgBox("Data Buku Sudah Ada Dalam List")
            Exit Sub
        End If
    Next
    lv1.Items.Add(txtkdbrng.Text)
    lv1.Items(n).SubItems.Add(txtnmbrng.Text)
    lv1.Items(n).SubItems.Add(txtharga.Text)
    lv1.Items(n).SubItems.Add(txtjmlhhrg.Text)
    lv1.Items(n).SubItems.Add(txttotal.Text)
    lv1.Items(n).SubItems.Add(txtjmlpsn.Text)
    lv1.Items(n).SubItems.Add(txtspesifikasi.Text)
    txttotal.Text = Format(CDbl(Total()), "###, ###, ###")
    ClearBarang()
    txtkdbrng.Focus()
End Sub

Function Total() As Double
    Dim ttl As Double = 0
    If Not Double.TryParse(txttotal.Text, Total) Then
        Total = 0
    End If
End Function

Private Sub btncetak_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btncetak.Click
    If txtnosph.Text = "" Or lv1.Items.Count = 0 Then
        MsgBox("Data Belum Lengkap", MsgBoxStyle.Information, "INFORMASI")
    Else
        Dim nilaikembali1, nilaikembali2 As Integer
        objsph.PNoSph = txtnosph.Text
        objsph.PTglSph = Format(dtpsph.Value, "yyy-MM-dd")
        objsph.PKdCs = txtkdcstmr.Text
        nilaikembali1 = objsph.Simpan()
        'menyimpan ke tabel Ada menggunakan perulangan
        For x As Integer = 0 To lv1.Items.Count - 1
            objada.PNoSph = txtnosph.Text
            objada.PKdBrg = lv1.Items(x).SubItems(1).Text
            objada.PKdBrg = CDbl(lv1.Items(x).SubItems(2).Text)
            objada.PKdBrg = CDbl(lv1.Items(x).SubItems(3).Text)
            nilaikembali2 = objada.Simpan()
            Dim objbarang As New ClsBarang
            objbarang.PKdBrg = lv1.Items(x).SubItems(0).Text
        Next
        If nilaikembali1 = 1 And nilaikembali2 = 1 Then
            MsgBox("Data Berhasil Disimpan", MsgBoxStyle.Information, "INFORMASI")
        End If
        ClearForm()
        ClearBarang()
        ClearCustomer()
        txtnosph.Text = objsph.AutoNumber
    End If
End Sub

Answer 1

これは、明示的または暗黙的に double にキャスト/変換された変数が実際には空の文字列であり、続行できないことを意味します。