从文本框中读取单曲

Question

这是我的潜艇：

    Protected Sub PrincipleTextBox_TextChanged(sender As Object, e As EventArgs)
    Try
        principle = Single.Parse(PrincipleTextBox.Text)
        PrincipleTextBox.BackColor = Drawing.Color.Empty
        ResultLabel.ForeColor = Drawing.Color.Black
        ResultLabel.Text = "hi"
    Catch ex As Exception
        PrincipleTextBox.BackColor = Drawing.Color.Pink
        ResultLabel.ForeColor = Drawing.Color.Red
        ResultLabel.Text = "Money values only for principle"
    End Try
    PrincipleTextBox.Text = FormatCurrency(principle)
End Sub

如果文本框中不是实数，我想阅读实数以了解原理和一些基本警告。所以，我输入 225 并不起作用（见图）。

为什么？

再次感谢您对我确定是一个基本问题的任何答案...仍在学习...

Answer 1

您需要通知 Parse 方法有关特定文化的货币符号的存在

Dim info = New CultureInfo("en-US")
Dim principle = Single.Parse(PrincipleTextBox.Text, NumberStyles.Currency, info)

但是，作为用户输入的输入，您应该以更具防御性的态度来处理转换问题。如果您的用户设法编写无法转换为数字的内容，那么最好使用

 Dim principle as Single
 Dim info = New CultureInfo("en-US")
 If Not Single.TryParse(PrincipleTextBox.Text, NumberStyles.Currency, info, principle) Then
     ' Code for invalid number input instead of catching the exception
      PrincipleTextBox.BackColor = Drawing.Color.Pink
      ResultLabel.ForeColor = Drawing.Color.Red
      ResultLabel.Text = "Money values only for principle"
 Else
    PrincipleTextBox.BackColor = Drawing.Color.Empty
    ResultLabel.ForeColor = Drawing.Color.Black
    ResultLabel.Text = "hi"
End If

并避免昂贵的异常驱动逻辑