从字符串“.”转换键入“十进制”无效

Question

我有一个用 Visual Basic 编写的单位转换器，使用 Visual Studio 2013。该程序运行良好，直到用户的初始输入为小数点。我收到此错误消息：从字符串“。”转换键入“十进制”无效。如何让该程序接受小数点作为用户的初始输入而不会导致程序崩溃？代码如下。

Private Function GetLength1(ByVal decLengthUnit1 As Decimal) As Decimal

Dim decResult1 As Decimal

If cboUnitType.SelectedItem = "Length" Then

    ' converts kilometer to...
    If cbo1.SelectedItem = "Kilometer" Then
        If cbo2.SelectedItem = "Kilometer" Then
            decResult1 = txtUnit1.Text
        ElseIf cbo2.SelectedItem = "Meter" Then
            decResult1 = (decLengthUnit1 * 1000)
        ElseIf cbo2.SelectedItem = "Centimeter" Then
            decResult1 = (decLengthUnit1 * 100000)
        ElseIf cbo2.SelectedItem = "Millimeter" Then
            decResult1 = (decLengthUnit1 * 1000000)
        ElseIf cbo2.SelectedItem = "Mile" Then
            decResult1 = (decLengthUnit1 * 0.621371191)
        ElseIf cbo2.SelectedItem = "Yard" Then
            decResult1 = (decLengthUnit1 * 1093.613297)
        ElseIf cbo2.SelectedItem = "Foot" Then
            decResult1 = (decLengthUnit1 * 3280.83989)
        ElseIf cbo2.SelectedItem = "Inch" Then
            decResult1 = (decLengthUnit1 * 39370.07868)
        End If
    End If
End If

Return decResult1.ToString().Trim("0") ' this is where I convert the data back to a string with some formatting
End Function


Private Sub txtUnit1_TextChanged(sender As Object, e As EventArgs) Handles      txtUnit1.TextChanged

    ' convert string to numeric data type
    Decimal.TryParse(txtUnit1.Text, decUnit1) ' this is where I convert user input to decimal data type

    ' handle String.Empty, or negative sign
    If txtUnit1.Text = "" OrElse txtUnit1.Text = "-" Then
        txtUnit2.Text = ""

    ElseIf cboUnitType.SelectedItem = "Length" Then
        suppressTextBox2TextChanged = True
        txtUnit2.Text = GetLength1(decUnit1)
        suppressTextBox2TextChanged = False

    End If

End Sub

Answer 1

您的函数设置为返回小数值

Private Function GetLength1(ByVal decLengthUnit1 As Decimal) As Decimal

您可以将其更改为字符串

Private Function GetLength1(ByVal decLengthUnit1 As Decimal) As String

或者你可以改变返回

Return Ctype(decResult1.ToString().Trim("0"), Decimal)

也可能是 Decimal 期望 , 而不是 . 我认为这与您拥有的文化设置有关。然后你可以改变你写的值或做一个REPLACE

Replace(decResult1.ToString().Trim("0"),".",",")

编辑

您也可以尝试更改txtUnit2.Text = GetLength1(decUnit1)

将其更改为 txtUnit2.Text = GetLength1(decUnit1).ToString().Trim("0") 并从函数内部删除 .Trim。

现在您正在修改文本框的 .Text，然后使用已经获得的 Decimal 值。

Answer 2

如果您有发生错误的情况，您通常可以执行以下操作：

val = 0
On Error Resume Next
val = someStatementThatMayCauseAnError
On Error Goto 0       ' turns error handling off again

这将为任何无法解析的输入返回0。

当然你也可以使用错误处理来告诉用户重试：

On Error Goto whoops
myString = contentsOfTextBox
val = convert(myString)
Exit Function
whoops:
MsgBox "Cannot convert " & myString & "; please try again"
End Function

最后 - 您可以显式测试导致问题的字符串。但是，如果您有一个导致问题的有效字符串，则问题可能出在您的解析函数上。例如，小数点与逗号是否存在问题？

Answer 3

提示：在您发布您的问题之前，我试图为我自己的学习提供一些数字验证代码，但我已经走到了这一步，我不会说它已经过全面测试，但到目前为止我还没有发现错误：

Class Program
    Private Shared Sub Main(args As String())
        'For testing, culture string nl-BE allows , as a decimal separator

        Dim d As Decimal = CheckNum(".", String.Empty)
        Console.WriteLine(d.ToString())
        Console.Read()
    End Sub



    Private Shared Function CheckNum(parm_toParseStr As String, parm_cultureName As String) As Decimal
        'Convert the string sent to decimal value and raise an exception if conversion falils
        'Expects string to validate and culture name (e.g. en-US). If culture name not passed, current is used
        'Takes care of the missing feature in try parse, namely when a string of only "." is passed, tryparse
        ' does not convert it to 0.

        Dim style As NumberStyles
        Dim culture As CultureInfo
        Dim result As Decimal

        If String.IsNullOrEmpty(parm_cultureName) Then
            parm_cultureName = Thread.CurrentThread.CurrentCulture.Name
        End If

        'for style see: http://msdn.microsoft.com/en-us/library/system.globalization.numberstyles%28v=vs.110%29.aspx
        style = NumberStyles.Number Or NumberStyles.AllowLeadingSign
        culture = CultureInfo.CreateSpecificCulture(parm_cultureName)

        parm_toParseStr = parm_toParseStr.Trim()

        If String.IsNullOrEmpty(parm_toParseStr) Then
            parm_toParseStr = "0"
        End If

        ' Gets a NumberFormatInfo associated with the passed culture.
        Dim nfi As NumberFormatInfo = New CultureInfo(parm_cultureName, False).NumberFormat
        If parm_toParseStr = "+" OrElse parm_toParseStr = "-" OrElse parm_toParseStr = nfi.CurrencyDecimalSeparator Then
            '+ - and decimal point
            parm_toParseStr = "0"
        End If

        'for tryparse see: http://msdn.microsoft.com/en-us/library/ew0seb73%28v=vs.110%29.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-2
        If [Decimal].TryParse(parm_toParseStr, style, culture, result) Then
            Return result
        Else
            Throw New ArgumentNullException("Could not convert the passed value of:{0}", parm_toParseStr)
        End If

    End Function
End Class