Question

我目前正试图在我的if / else语句中找到错误我运行了一些小测试，看看我的变量是否保持值，但是当我点击提交按钮时，我一直变为零。

Partial Class _Default
    Inherits System.Web.UI.Page

Protected Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles Pack_Weight.TextChanged

End Sub

Protected Sub Submit_Button_Click(sender As Object, e As EventArgs) Handles Submit_Button.Click
    Dim PackageW, MemphisRate, SanFranRate As Double

    'takes user input from the textbox and places it in the variable
    PackageW = Pack_Weight.Text

    'if user selects the dropbox and radiobutton list the selected combo should charge a varying bag fee
    If Location.SelectedValue = "1" & ShippingList.SelectedValue = "1" Then
        MemphisRate = 2.2 * PackageW

    ElseIf Location.SelectedValue = "1" & ShippingList.SelectedValue = "2" Then
        MemphisRate = 2.59 * PackageW

    ElseIf Location.SelectedValue = "1" & ShippingList.SelectedValue = "3" Then
        MemphisRate = 2.92 * PackageW

    End If
    'outputs the user selected combo to the total amount textbox
    Total_Cost.Text = MemphisRate

    If Location.SelectedValue = "2" & ShippingList.SelectedValue = "1" Then
        SanFranRate = 2.2 * PackageW

    ElseIf Location.SelectedValue = "2" & ShippingList.SelectedValue = "2" Then
        SanFranRate = 2.59 * PackageW

    ElseIf Location.SelectedValue = "2" & ShippingList.SelectedValue = "3" Then
        SanFranRate = 2.92 * PackageW

    End If

    Total_Cost.Text = SanFranRate

End Sub
End Class

Answer 1

您错误地使用了&。在VB.NET中，&运算符用于字符串连接。您应该使用关键字And或AndAlso代替。

Answer 2

在尝试处理输入之前，您应该执行输入验证。

使用Option Strict On可确保所有数据类型都匹配，例如它会阻止你尝试将字符串分配给数字变量。

当您计算货币值时，最好使用Decimal类型而不是Double。

其中有很多If... ElseIf - 使用Select Case看起来有点整洁，如下所示：

Option Strict On
' ...

Protected Sub Submit_Button_Click(sender As Object, e As EventArgs) Handles Submit_Button.Click
    Dim packageW As Decimal

    ' INPUT VALIDATION
    If Not Decimal.TryParse(Pack_Weight.Text, packageW) Then
        ' inform user that a number is required
        Exit Sub
    End If

    If Location.SelectedIndex = -1 Then
        ' inform user that a location must be selected
        Exit Sub
    End If

    If ShippingList.SelectedIndex = -1 Then
        ' inform user that a shipping type must be selected
        Exit Sub
    End If

    ' CALCULATE SHIPPING COST
    Dim shippingRate As Decimal = 0D

    Select Case Location.SelectedItem.Text
        Case "1" ' Memphis
            Select Case ShippingList.SelectedItem.Text
                Case "1" ' Economy
                    shippingRate = 2.2D
                Case "2" ' Normal
                    shippingRate = 2.59D
                Case "3" ' Speedy
                    shippingRate = 2.92D
            End Select

        Case "2" ' San Francisco
            Select Case ShippingList.SelectedItem.Text
                Case "1"
                    shippingRate = 2.2D
                Case "2"
                    shippingRate = 2.59D
                Case "3"
                    shippingRate = 2.92D
            End Select

    End Select

    Dim shippingCost As Decimal = Math.Round(packageW * shippingRate, 2)
    Total_Cost.Text = shippingRate.ToString()

End Sub

我发现.SelectedItem.Text比.SelectedValue更可靠。

我不清楚某些变量的名称是什么 - 你应该改变它们才有意义。

从代码中的注释中可以看出，如果没有选择的状态是有效的 - 如果是，请取出.SelectedIndex = 1的检查。您可能希望确保用户输入了有效的packageW，即不是负数且不是非常大。

如果声明没有给出正确的答案ASP.NET

2 个答案: