Question

你好我正在编写一个简单的VB表单，到目前为止一切都很好。但是，如果我为“SpaceLeftText.Text”留下一个空白输入框并点击回车，我会收到此错误：

“Microsoft.VisualBasic.dll中发生了'System.InvalidCastException'类型的未处理异常

其他信息：从字符串“”到“Double”类型的转换无效。

以下是我正在使用的代码：

Public Class Form1

Private Sub EnterButton_Click(sender As Object, e As EventArgs) Handles EnterButton.Click, MyBase.Activated


    SpaceLeftText.Text = Math.Round((((Val(AxleLengthText.Text - 12.7) / 2) - 1.59 - 3)), 2)

    Dim count As Decimal
    count = SpaceLeftText.Text

    If count > 10 Then
        TenText.Text = Int(count / 10)
        count = count - (TenText.Text * 10)
    Else : TenText.Text = 0
    End If

    If count > 4 Then
        FourText.Text = Int(count / 4)
        count = count - (FourText.Text * 4)
    Else : FourText.Text = 0
    End If

    If count > 2 Then
        TwoText.Text = Int(count / 2)
        count = count - (TwoText.Text * 2)
    Else : TwoText.Text = 0
    End If

    If count > 1.5 Then
        OnePointFiveText.Text = Int(count / 1.5)
        count = count - (OnePointFiveText.Text * 1.5)
    Else : OnePointFiveText.Text = 0
    End If

    If count > 1 Then
        OneText.Text = Int(count / 1)
        count = count - (OneText.Text * 1)
    Else : OneText.Text = 0
    End If

End Sub
Private Sub ResetButton_Click(sender As System.Object, e As System.EventArgs) Handles ResetButton.Click
    AxleLengthText.Clear()
    SpaceLeftText.Clear()
    TenText.Clear()
    FourText.Clear()
    TwoText.Clear()
    OnePointFiveText.Clear()
    OneText.Clear()
    GapText.Clear()
    QuadRingText.Clear()
    OringSpacerText.Clear()
    FitText.Clear()
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

End Sub

End Class

所以我在Dim Count上面添加了以下代码作为十进制：

 If SpaceLeftText.Text = "" Then
        MsgBox("Please Enter Axle Length!")
    Else

但现在一旦我运行它，没有按下输入并留下一个空白的输入框我立即得到我的消息框说“请输入轴长度”。我点击确定，然后在进入程序之前立即弹出大约14次。有没有人有任何意见。我不知道我做错了什么。谢谢。

Answer 1

由于您的事件正在处理（MyBase.Activated），因此该消息显示14次。

请尝试以下方法：

Private Sub EnterButton_Click(sender As Object, e As EventArgs) Handles EnterButton.Click

还要确保（AxleLengthText.Text）不为空，并且有效转换为double值，如下所示：

dim tmpDouble as double

if not string.isNullOrEmpty(AxleLengthText.Text) andalso Double.TryParse(AxleLengthText.Text, tmpDouble ) Then
    SpaceLeftText.Text = Math.Round((((Val(tmpDouble - 12.7) / 2) - 1.59 - 3)), 2)
end If

有关空白输入框和错误转换字符串的VB代码的问题＆＃34;＆＃34;加倍

1 个答案: