vb.net 代碼中將字符串“”類型轉換為雙精度無效異常

Question

我正在嘗試上傳一個包含兩條記錄的 csv 文件。 下面的代碼執行了兩次，第三次我得到了這個異常----類型字符串“”的轉換無效我放了一個調試器，在那里我找到了 excel 表的兩列的值，但是第三次我得到了這個例外。 非常感謝您的幫助。 下面是代碼。

  Public Function GetLocationInformation(stream As Stream) As List(Of CsvPropLocation) _
        Implements ICsvHandling.GetLocationInformation
        If stream Is Nothing Then Return Nothing

        Dim locations = New List(Of CsvPropLocation)
        Using reader = New StreamReader(stream)
            Dim config = New CsvConfiguration(CultureInfo.InvariantCulture) With {
                .HasHeaderRecord = True,
                .IgnoreBlankLines = False
            }
            Using csv = New CsvReader(reader, config)
                Using dataReader As New CsvDataReader(csv)
                    Dim dt = New DataTable()
                    dt.Load(dataReader)
                    For Each row As DataRow In dt.Rows
                        Dim propLocation As CsvPropLocation
                        'find or create a propLocation
                        If locations.Any(Function(x) x.nLocationNumber = row("LocNum")) Then       ######Got exception here ######
                            propLocation = locations.First(Function(x) x.nLocationNumber = row("LocNum"))
                        Else
                            propLocation = New CsvPropLocation(row("LocNum"))
                            locations.Add(propLocation)
                        End If
                        'do building stuff.
                        Dim building = ParseRowIntoBuilding(row)
                        propLocation.AddBuilding(building)
                    Next
                End Using
            End Using
        End Using
        Return locations
    End Function

Answer 1

將您的線路更改為

Dim number As Double
If Double.TryParse(row("LocNum"), number ) AndAlso locations.Any(Function(x) x.nLocationNumber = number )

這樣，您可以確保 number 只有在從 row("LocNum") 獲取有效值時才會被評估

另請記住，必須控制 Else 部分，因為 New CsvPropLocation(row("LocNum")) 可能期望一個不在位置內的有效 Double ，因此更改為：

Else If Double.TryParse(row("LocNum"), number ) 'You can check against number = 0 
         'if zero isn't a valid value for number 
         '(or initialize number to a known invalid value and check against it)
         'if yuo didn't want a double try parse
    propLocation = New CsvPropLocation(number)
    locations.Add(propLocation)
End If