输入字符串格式不正确 vb.net

Question

我在文本label中出现错误问题，请问还有其他解决方案吗？

谢谢

 Private Sub CalculateGrandTotal()
            Dim tot As Double = 0
'error this below code 
            Dim cash As Double = Double.Parse(lblDisTotal.Text)
            For Each item As DataGridViewRow In grid.Rows
                tot += Double.Parse(item.Cells(5).Value.ToString())
            Next item
            lblGrandTotal.Text = (tot * (1 - cash / 100)).ToString("N2")
        End Sub
  Private Sub BtnRefresh_Click(sender As Object, e As EventArgs) Handles BtnRefresh.Click
 lblDisTotal.Text = ""
        End Sub

Answer 1

当按钮事件被刷新时 lblDisTotal 不会变成空白而是变成“0” 那么问题就解决了

 Private Sub CalculateGrandTotal()
            Dim tot As Double = 0
'error this below code 
            Dim cash As Double = Double.Parse(lblDisTotal.Text)
            For Each item As DataGridViewRow In grid.Rows
                tot += Double.Parse(item.Cells(5).Value.ToString())
            Next item
            lblGrandTotal.Text = (tot * (1 - cash / 100)).ToString("N2")
        End Sub
  Private Sub BtnRefresh_Click(sender As Object, e As EventArgs) Handles BtnRefresh.Click
 lblDisTotal.Text = "0"
        End Sub

Answer 2

适当的解决方案是Double.TryParse来处理有人在您的文本框中键入“hello world”（如果它未经过清理）。

通常，您应该尽可能避免使用 .parse 并选择尝试解析，除非您可以绝对确定您的值可以解析为您想要的类型。 否则，使用 tryParse 来防止可以防止的异常。

Private Sub CalculateGrandTotal()
    Dim tot As Double = 0
'error this below code 
    Dim cash As Double
    'tryParse returns a boolean indicating successful parsing. You can check for that, however, if it fails, it assigns 0 to your passed in double

    Double.TryParse(lblDisTotal.Text, cash)
    For Each item As DataGridViewRow In grid.Rows
        dim val as double
        Double.TryParse(item.Cells(5).Value, val)
        tot += val
    Next item
    lblGrandTotal.Text = (tot * (1 - cash / 100)).ToString("N2")
End Sub

Private Sub BtnRefresh_Click(sender As Object, e As EventArgs) Handles BtnRefresh.Click
    lblDisTotal.Text = ""
End Sub