vb.net - 如何删除此 GoTo？

Question

我很好奇是否可以解析数据类型的输入框，如果它与数据类型不匹配，它将循环直到完成正确的类型。我了解如何使用范围来做到这一点，但如果可能的话，我宁愿不这样做。

我的代码是:

Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
    Dim amountAssignments As Integer
    Dim pointsEarned As Integer = 0
    Dim pointsEarnedTotal As Integer = 0
    Dim pointsPossible As Integer = 0
    Dim pointsPossibleTotal As Integer = 0
    Dim Assignment As Integer = 1

    Integer.TryParse(txtAmount.Text, amountAssignments)

    Do Until Assignment > amountAssignments
        txtAmount.Text = String.Empty
        pointsEarned = Integer.Parse(InputBox("Please enter the amount, as a whole number, of Points Earned for Assignment " & Assignment & ":"))
        On Error GoTo Check
        pointsEarnedTotal = pointsEarnedTotal + pointsEarned
        pointsPossible = Integer.Parse(InputBox("Please enter the amount, as a whole number, of Points Possible for Assignment " & Assignment & ":"))
        On Error GoTo Check
        pointsPossibleTotal = pointsPossibleTotal + pointsPossible
        Assignment = Assignment + 1
    Loop

    lblGrade.Text = (pointsEarnedTotal / pointsPossibleTotal)
Check:
    MessageBox.Show("An error has occured, most likely due to an improper value in the points earned or possible box. Please try running the program again with proper values.", "Please run the program again", _
                    MessageBoxButtons.OK, MessageBoxIcon.Asterisk)

End Sub

我知道 GoTo 不是“正确”或首选的解决方案，但我更多地将其用作临时占位符。任何帮助将不胜感激，因为这超出了我目前的编程能力。

Answer 1

我会考虑将 Integer.TryParse 用于所有转换而不是 Parse，这样您就可以测试转换是否失败而没有抛出和错误。像这样的东西应该工作

If Integer.TryParse(txtAmount.Text, amountAssignments) Then
    Do Until Assignment > amountAssignments
        txtAmount.Text = String.Empty
        If Not Integer.TryParse(InputBox("Please enter the amount, as a whole number, of Points Earned for Assignment " & Assignment & ":"), pointsEarned) Then
            showError()
            Exit Sub
        End If
        pointsEarnedTotal = pointsEarnedTotal + pointsEarned
        If Not Integer.TryParse(InputBox("Please enter the amount, as a whole number, of Points Possible for Assignment " & Assignment & ":"), pointsPossible) Then
            showError()
            Exit Sub
        End If
        pointsPossibleTotal = pointsPossibleTotal + pointsPossible
        Assignment = Assignment + 1
    Loop
    lblGrade.Text = (pointsEarnedTotal / pointsPossibleTotal)
Else
    showError()
End If

您的消息框已放入这样的子例程中。

Sub showError()
    MessageBox.Show("An error has occured, most likely due to an improper value in the points earned or possible box. Please try running the program again with proper values.", "Please run the program again", _
     MessageBoxButtons.OK, MessageBoxIcon.Asterisk)
End Sub