Question

我无法弄清楚我的代码有什么问题。该代码应该使用成本，数量和促销代码来计算项目的总成本（如果您有）。当我放入!等未使用的字符时，它会一直崩溃。欢迎任何帮助或改进。

Public Class Form1

Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click
    Dim decDisplayTotal As Decimal
    Dim decPrice As Decimal = txtPrice.Text
    Dim intQuantity As Integer = txtQuantity.Text
    Dim strPromoCode As String = txtPromoCode.Text


    decDisplayTotal = decPrice * intQuantity
    lblDisplayTotal.Text = "$" & decDisplayTotal
    If decPrice < 0 Then
        lblDisplayTotal.Text = ("")
        txtPrice.Text = Nothing
        txtQuantity.Text = Nothing
        txtPromoCode.Text = Nothing
        MessageBox.Show("Please enter an appropriate price.", "Invalid Input")
    End If
    If intQuantity < 0 Then
        lblDisplayTotal.Text = ("")
        txtPrice.Text = Nothing
        txtQuantity.Text = Nothing
        txtPromoCode.Text = Nothing
        MessageBox.Show("Please enter an approriate quantity.", "Invalid Input")
    End If
    If strPromoCode = ("132") Then
        MessageBox.Show("You used a limited time, 10% off code! Watch your price drop 10%!", "10% off")
        decDisplayTotal = 0.9 * (decPrice * intQuantity)
        lblDisplayTotal.Text = "$" & decDisplayTotal
    End If
    If strPromoCode = ("129") Then
        MessageBox.Show("You used a limited time, 20% off code! Watch your price drop 20%!", "20% off")
        decDisplayTotal = 0.8 * (decPrice * intQuantity)
        lblDisplayTotal.Text = "$" & decDisplayTotal
    End If
    If strPromoCode = ("136") Then
        MessageBox.Show("You used a limited time, 30% off code! Watch your price drop 30%!", "30% off")
        decDisplayTotal = 0.7 * (decPrice * intQuantity)
        lblDisplayTotal.Text = "$" & decDisplayTotal
    End If
    If strPromoCode = ("264") Then
        MessageBox.Show("You used a limited time, buy 1 get 1 free code, so watch your total cut in half!", "Buy 1 Get 1 Free")
        decDisplayTotal = 0.5 * (decPrice * intQuantity)
        lblDisplayTotal.Text = "$" & decDisplayTotal
    End If
    If strPromoCode = ("125") Then
        decDisplayTotal = (decPrice * intQuantity)
        lblDisplayTotal.Text = "$" & decDisplayTotal
    End If
    Try
        decPrice = Convert.ToInt16(txtPrice.Text)
    Catch ex As Exception
        lblDisplayTotal.Text = Nothing
        MessageBox.Show("Please enter an acceptable price.", "Invalid Input")
        txtPrice.Text = Nothing
    End Try
    Try
        intQuantity = Convert.ToInt16(txtQuantity.Text)
    Catch ex As Exception
        lblDisplayTotal.Text = Nothing
        MessageBox.Show("Please enter an acceptable quanitity.", "Invalid Input")
        txtQuantity.Text = Nothing
    End Try
    Try
        strPromoCode = Convert.ToInt16(txtPromoCode.Text)
    Catch ex As Exception
        lblDisplayTotal.Text = Nothing
        MessageBox.Show("Please enter a valid Promo Code.", "Invalid Input")
        txtPromoCode.Text = Nothing
    End Try
End Sub
Private Sub txtPrice_TextChanged(sender As Object, e As EventArgs) Handles txtPrice.TextChanged
    lblDisplayTotal.Text = ("")

End Sub

Private Sub txtQuantity_TextChanged(sender As Object, e As EventArgs) Handles txtQuantity.TextChanged
    lblDisplayTotal.Text = ("")

End Sub

Private Sub txtPromoCode_TextChanged(sender As Object, e As EventArgs) Handles txtPromoCode.TextChanged
    lblDisplayTotal.Text = ("")

End Sub



End Class

Answer 1

要清楚理解的第一件事是字符串不是数字。 VB允许这种松弛，但它以许多微妙的方式咬回来。我假设您将单点放在任何文本框中，然后尝试使用该TEXT，因为它是一个字符串。有时它不会有效。

正确的方法是让框架尝试转换，如果失败则通知您的用户该问题。

因此，不使用各种Convert.ToXXXXx而是使用SomeType.TryParse（I.E. Int32.TryParse）

 Dim decPrice As Decimal
 Dim intQuantity As Integer
 Dim strPromoCode As String

 if Not Decimal.TryParse(txtPrice.Text, decPrice) Then
    MessageBox.Show("Please type a valid number for Price")
    ClearInputs()
    return
 End if

 if Not Int32.TryParse(txtPrice.Text, intQuantity) Then
    MessageBox.Show("Please type a valid number for Quantity")
    ClearInputs()
    return
 End if

 Private Sub ClearInputs()
    lblDisplayTotal.Text = ""
    txtPrice.Text = ""
    txtQuantity.Text = ""
    txtPromoCode.Text = ""
 End Sub

现在您输入的值存储在正确的数据类型变量中，您可以继续执行代码的其余部分.....

....
decDisplayTotal = decPrice * intQuantity
lblDisplayTotal.Text = "$" & decDisplayTotal.ToString
....

您需要为项目设置的重要配置是项目属性中的Option Strict On。此配置将禁止字符串和数字之间的隐式转换，并强制您编写更正确的代码。

顺便说一句，在检查strPromoCode之后，您不需要再次重复将文本框中的字符串转换为相应变量的过程

语法错误 - 无法计算

1 个答案: