Question

我的程序中有一个错误的错误，如果用户在文本框中没有输入时按下check（计算）按钮，程序会显示以下错误：“从字符串转换”“到'Double'类型无效“。我想解决这个问题，但我不知道如何进行转换。我在想CType但是我听到了解析的话题。我该怎么做？文本框称为mskTxtInput，按钮对象称为btnCheck，它执行所有计算和处理。

更新：这是我的代码，除了解析方法，所以希望这有点帮助！

Private Sub btnCheck_Click（ByVal sender As System.Object，ByVal e As System.EventArgs）处理btnCheck.Click pic1.Visible = False'隐藏图片 pic1.Image = My.Resources.A pic2.Image = My.Resources.F

    Dim value As Double
    If Double.TryParse(mskTxtInput.Text, value) = Then
        MsgBox("parsing success") ' parsing worked, so use the value in here 
    Else
        MsgBox("parsing failed") ' parsing failed, so alert the user to that fact 
    End If


    If radAdd.Checked = True Then
        totalNum = num1 + num2


    End If

    If radSub.Checked = True Then
        totalNum = num1 - num2

    End If

    If radMulti.Checked = True Then
        totalNum = num1 * num2



    End If

    If mskTxtInput.Text = totalNum Then
        lblAns.Text = ("Correct!")
        lblAns2.Text = ("Answer is " & totalNum)
        pic1.Visible = True
        wins = wins + 1
        nScore = wins



    Else
        lblAns.Text = ("Incorrect")
        lblAns2.Text = ("Answer should be " & totalNum)
        pic2.Visible = True

    End If

    attempts = attempts + 1
    If attempts = 5 Then
        MessageBox.Show("Game Finished! ", "End Of Game", _
                        MessageBoxButtons.OK, _
                        MessageBoxIcon.Exclamation)
        lblAns.Text = ("You scored " & wins & " Out of 5")
        btnSpin.Enabled = False
        pic1.Visible = False
        pic2.Visible = False
        lblAns2.Text = ""
        lblAns2.Text = "Play again?"
        btnCheck.Enabled = False
        btnNew.Enabled = True
        attempts = 0
        wins = 0
    End If


    mskTxtInput.Clear()
    mskTxtInput.Focus()


End Sub

Answer 1

尝试使用Double.TryParse Method (String, Double)而不是

像

这样的东西

Dim s As String
Dim result As Double
Dim returnValue As Boolean

returnValue = Double.TryParse(s, result)

Answer 2

使用TryParse方法进行解析，以避免在解析失败时出现异常：

Dim value As Double
If Double.TryParse(mskTxtInput.Text, value) Then
  ' parsing worked, so use the value in here
Else
  ' parsing failed, so alert the user to that fact
End If

Answer 3

将iVar调整为整数 dim sStr as string

SSTR = “”

ivar = val（sstr）

Answer 4

使用静态方法Double.TryParse()。如果它返回true，则解析成功，您可以继续操作。如果它返回false，则解析不成功，您应该显示一条错误消息（如果需要，使用MessageBox）并中止操作。

VB.Net从字符串转换为double

4 个答案: