vb.net 使用 TryParse 方法将字符串“”转换为“Double”类型无效
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Conversion from string "" to type 'Double' is not valid using TryParse Method
提问by OneFineDay
I have a simple addition program in VB.Net and I am attempting to test if the textbox is only taking in a number and not any letters. I need to use the TryParse method, and I cannot figure out wny I am still receiving this error. Pls Help
我在 VB.Net 中有一个简单的加法程序，我试图测试文本框是否只接收数字而不是任何字母。我需要使用 TryParse 方法，但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
回答by OneFineDay
This is how you use the TryParse:
这是您使用 TryParse 的方式：
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
End the code block if text is empty:
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
