system.invalidcastexception 'conversion from string to type 'double' is not valid.' vb.net

Question

system.invalidcastexception 'conversion from string to type 'double' is not valid.

    ' vb.net
    receiptDetails = lstReceipt.SelectedItem
    Dim newTotalAmount As Double = CDbl(receiptDetails.Remove(0, 94))

    lstReceipt.Items.RemoveAt(lstReceipt.SelectedIndex)
    totalAmount -= newTotalAmount

    txtTotal.Text = totalAmount.ToString("GH₵###,###.00")
    txtDiscount.Text = discountAmount.ToString("GH₵###,###.00")
    txtTaxableAmount.Text = TaxableAmount.ToString("GH₵###,###.00")
    txtVat.Text = taxAmount.ToString("GH₵###,###.00")
    txtPayableAmount.Text = payableAmount.ToString("GH₵###,###.00")

End Sub

Answer 1

If I had to guess, the code is failing at:

Dim newTotalAmount As Double = CDbl(receiptDetails.Remove(0, 94))

I suggest using TryParse instead of CDbl to verify that the value can be converted to a Double. If the result of TryParse is False, then display the value that attempted to be converted:

Dim massagedValue As String = receiptDetails.Remove(0, 94)
Dim newTotalAmount As Double
If (Double.TryParse(massagedValue, newTotalAmount)) Then
    ' continue business logic ...
Else
    MessageBox.Show($"The following value is not a valid double: {massagedValue}", "Invalid Double", MessageBoxButtons.OK, MessageBoxIcon.Error)
End If

Now when you get the user-friendly error message you can determine why the value is not able to be converted to a double.

My best guess is that you are not removing enough or are removing too much characters from the receiptDetails variable.