Question

我刚开始上VB的第一堂课，我的老师在48小时内没有回复电子邮件，我的项目即将到期。我希望你们能帮助我解决这个问题。我想要做的是获得一个程序来计算3个文本框的总数，并将其显示在一个标签中。问题是，3个文本框中的输入不能是负数。我试图设置它，所以当输入负数时，它会显示一条消息，只输入正数。但是，每次运行程序时，它只计算带有负数的文本框为0，并完成剩余的计算。这是我的代码：

Private Sub btnCalc_Click(sender As Object, e As EventArgs) Handles btnCalc.Click
    Dim intPackA As Integer
    Dim intPackB As Integer
    Dim intPackC As Integer
    Dim intCalc As Integer
    Try
        If txtPackA.Text Or txtPackB.Text Or txtPackC.Text <= 0 Then
            lblCalc.Text = "Please enter positive numeric values"
        End If
        If txtPackA.Text >= 0 Then
            intPackA = txtPackA.Text * 79.2
        Else
            lblCalc.Text = "Please enter positive numeric values"
        End If
        If txtPackB.Text >= 0 Then
            intPackB = txtPackB.Text * 119.4
        Else
            lblCalc.Text = "Please enter positive numeric values"
        End If

        If intPackC >= 0 Then
            intPackC = txtPackC.Text * 149.5
        Else
            lblCalc.Text = "Please enter positive numeric values"
        End If

        intCalc = intPackA + intPackB + intPackC

        lblCalc.Text = "Package A:  " & intPackA.ToString("c") + vbCrLf & "Package B:  " & intPackB.ToString("c") + vbCrLf & "Package C:  " & intPackC.ToString("c") + vbCrLf + vbCrLf & "Grand Total: " & intCalc.ToString("c")
    Catch
        lblCalc.Text = "Please enter positive numeric values"
    End Try

End Sub

我知道其他一些if语句是多余的，但是如果你能给我一些简单的方法来浓缩和清理，我会很感激。

Answer 1

首先使用TryParse将您的String输入从Textbox转换为Integer（并将其存储到Integer变量），然后进行比较：

    Dim valueA, valueB, valueC As Integer
    Dim intPackA, intPackB, intPackC, intCalc As Integer

    Int32.TryParse(txtPackA.Text, valueA)
    Int32.TryParse(txtPackB.Text, valueB)
    Int32.TryParse(txtPackC.Text, valueC)

    If valueA <=0 Or valueB <= 0 Or valueC <= 0 Then
        lblCalc.Text = "Please enter positive numeric values"
        Exit Sub
    End If

做其余的服务，否则你就没有更多的学习经验了。

Answer 2

而不是

  If txtPackA.Text Or txtPackB.Text Or txtPackC.Text <= 0 Then
            lblCalc.Text = "Please enter positive numeric values"
   End If

使用此

If txtPackA.Text <= 0 Then
    lblCalc.Text = "Please enter positive numeric values"
    txtPackA.Focus()
    Exit Sub
ElseIf txtPackB.Text <= 0 Then
    lblCalc.Text = "Please enter positive numeric values"
    txtPackB.Focus()
    Exit Sub
ElseIf txtPackC.Text <= 0 Then
    lblCalc.Text = "Please enter positive numeric values"
    txtPackC.Focus()
    Exit Sub
End If

Answer 3

你需要这个........

Private Sub TB_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtPackA.KeyPress, txtPackB.KeyPress, txtPackC.KeyPress

    Dim sN As String = "0123456789"
    Dim sO As String = Chr(8) & Chr(13) & Chr(1) & Chr(3) & Chr(22)        

    If Not (sN & sO).Contains(e.KeyChar) Then

        e.Handled = True   

    End If

End Sub


Private Sub TB_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtPackA.TextChanged, txtPackB.TextChanged, txtPackC.TextChanged

     lblCalc.Text = format(val(txtPackA.Text) + val(txtPackB.Text) + val(txtPackC.Text))

End Sub

VB防止负整数

3 个答案: