Question

我在VB.Net中有一个简单的添加程序，我试图测试文本框是否仅包含数字而不是任何字母。我需要使用TryParse方法，我无法弄清楚，我仍然收到此错误。请帮助

Public Class perrySolutionForm
Dim numberOne As Double
Dim numberTwo As Double

Public Function sum(ByRef numberOne As Double, ByRef numberTwo As Double)
    sum = Val(numberOne) + Val(numberTwo)
End Function

Public Function difference(ByRef numberOne As Double, numberTwo As Double)     

difference = Val(numberOne) - Val(numberTwo)

End Function

Private Sub sumButton_Click(sender As Object, e As EventArgs) Handles sumButton.Click
    If numberOneInput.Text = "" Then
        MessageBox.Show("Both fields must be filled out.")
        If Double.TryParse(numberOneInput.Text, numberOne) Then
            MessageBox.Show("Success")
            'numberOne has a Double value
        Else
            MessageBox.Show("Failure")
            'numberOne = Nothing
        End If
    Else
        outputLabel.Text = sum(numberOne, numberTwo)
    End If
End Sub

Private Sub numberOneInput_TextChanged(sender As Object, e As EventArgs) Handles numberOneInput.TextChanged
    numberOne = numberOneInput.Text

End Sub

Private Sub numberTwoInput_TextChanged(sender As Object, e As EventArgs) Handles numberTwoInput.TextChanged
    numberTwo = numberTwoInput.Text

End Sub

Answer 1

这就是你使用TryParse的方法：

If Double.TryParse(numberOneInput.Text, numberOne) Then
  'code for a success
  'numberOne has a Double value
Else
  'code for a failure
  'numberOne = Nothing
End If

如果文本为空，则结束代码块：

If String.IsNullOrWhiteSpace(numberOneInput.Text) Then 
   MessageBox.Show("Value is incorrect format")
   Exit Sub
End If

使用TryParse方法从字符串“”到“Double”类型的转换无效

1 个答案: