vb.net - 从字符串 "."到类型 'Decimal' 的转换无效

Question

我有一个用 Visual Basic 编写的单位转换器，使用 Visual Studio 2013。该程序工作正常，直到用户的初始输入是小数点。我收到此错误消息:从字符串“.”转换输入“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十进制值

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

或者您可以更改返回

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

也可能是 Decimal 需要 , 而不是 。 我认为这与您的文化设置有关。然后您可以更改已写入的值或执行 REPLACE

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

编辑

您还可以尝试更改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，然后使用已获得的Decimal值。