Input string was not in a correct format in vb,net-CodePudding

I have an error problem in the text label. Is there another solution?

Thanks

 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

CodePudding user response：

when the button event is refreshed then lblDisTotal does not become blank but becomes "0" then the problem is solved

 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

CodePudding user response：

The appropriate solution would be Double.TryParse to handle someone typing "hello world" into your text box if it is not sanitized.

As a rule, you should avoid .parse whereever possible and opt for try parse unless you can guarantee with absolute certainty that your value CAN be parsed into the type you want. Otherwise, utilize tryParse to prevent exceptions that can be prevented.

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