Question

我是学习Visual Basic的新程序员。现在，我正在做一个有关垒球记分牌的项目。我已经在这个项目上工作了一段时间，但我对一件事情感到困惑。

让我感到困惑的是，我在一个消息框中输入了一个无效的负数输入，但它并没有从lstScores中删除它，即使该消息框出现了，它仍然算作一局输入。

If runs < 0 Then
            MessageBox.Show(VALID_MESSAGE)

这是代码：

Public Class frmSoftballScoreboard
    Const VALID_MESSAGE As String = "Enter valid runs value"
    Const ONLY_MESSAGE As String = "Only seven innings are allowed"
    'Declaring array
    Dim scores(6) As Double
    'declaring variables
    Dim runs As String
    Dim runningScore As Integer = 0
    Dim i As Integer = 0
    Dim out As Double

    'page load event
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        lstScores.Items.Add("Runs : Running Score")
    End Sub
    'Enter score button
    Private Sub btnScore_Click(sender As Object, e As EventArgs) Handles btnScore.Click

        If i < scores.Length Then
            'display inputbox to the user
            runs = InputBox("Enter score for " & (i + 1) & " innings", "Score")
            'if runs is entered
            If runs <> "" Then
                'parse the value of runs
                If (Double.TryParse(runs, out)) Then
                    'parse the runs and add it to the array scores()
                    scores(i) = Double.Parse(runs)
                    runningScore += scores(i)
                    'add the rainfall value to the listbox along with month name
                    lstScores.Items.Add(scores(i) & " :" & runningScore)
                    'increment the value of i
                    i = i + 1
                Else
                    'display error message
                    MessageBox.Show(VALID_MESSAGE)
                    lblTotal.Text = ""
                End If
            Else
                'if runs is empty then display error message
                MessageBox.Show("Enter runs for " & i & "innings")
            End If
        Else
            MessageBox.Show(ONLY_MESSAGE)
        End If
        If runs < 0 Then
            MessageBox.Show(VALID_MESSAGE)
        End If
        'calculate total runs And display on the lable
        If scores(6) = 7 Then
            lblTotal.Text = String.Format("final score is {0}", scores.Sum())
        End If
    End Sub
    'Clear Menu click
    Private Sub ClearToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles mnuClear.Click
        lstScores.Items.Clear()
        lblTotal.Text = ""
        'reset i to 0
        i = 0
    End Sub
    'Exit Menu click
    Private Sub ExitToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles mnuExit.Click
        'close application
        Application.Exit()
    End Sub
End Class

如果您能提供帮助，我将不胜感激。谢谢。

Answer 1

 Private Sub btnScore_Click(sender As Object, e As EventArgs) Handles btnScore.Click
    If i < scores.Length Then
        'display inputbox to the user
        runs = InputBox("Enter score for " & (i + 1) & " innings", "Score")
        'if runs is entered
        If runs < 0 Then
            MessageBox.Show(VALID_MESSAGE)
            Exit Sub
        ElseIf runs <> "" Then
            'parse the value of runs
            If (Double.TryParse(runs, out)) Then
                'parse the runs and add it to the array scores()
                scores(i) = Double.Parse(runs)
                runningScore += scores(i)
                'add the rainfall value to the listbox along with month name
                lstScores.Items.Add(scores(i) & " :" & runningScore)
                'increment the value of i
                i = i + 1
            Else
                'display error message
                MessageBox.Show(VALID_MESSAGE)
                lblTotal.Text = ""
            End If
        Else
            'if runs is empty then display error message
            MessageBox.Show("Enter runs for " & i & "innings")
        End If
    Else
        MessageBox.Show(ONLY_MESSAGE)
    End If
    If runs < 0 Then
        MessageBox.Show(VALID_MESSAGE)
    End If
    'calculate total runs And display on the lable
    If scores(6) = 7 Then
        lblTotal.Text = String.Format("final score is {0}", scores.Sum())
    End If
End Sub

这就是为什么如果您输入无效数据，它将添加到lstScores中的原因，因为您的If statement..位于代码的底部，尽管不建议您将If else statement..放在哪里。请记住，阅读代码是从上到下开始的。

您的第一个If statement就是这样。 If runs <> "" then ....，当然，如果您在-1中输入Input Text值，则布尔值将为true If -1 <> "" = true，然后它将继续执行

 If (Double.TryParse(runs, out)) Then
    'parse the runs and add it to the array scores()
     scores(i) = Double.Parse(runs)
     runningScore += scores(i)
     'add the rainfall value to the listbox along with month name
     lstScores.Items.Add(scores(i) & " :" & runningScore)
     'increment the value of i
     i = i + 1

这是代码行，即使该值无效还是仍然在lstScores，lstScores.Items.Add(scores(i) & " :" & runningScore)

中添加值

现在，在该语句之后，您将收到一条消息：

输入有效的运行值

 If runs < 0 Then
        MessageBox.Show(VALID_MESSAGE)
 End If

该代码是您收到消息的原因。如果您当然输入-1，则布尔值的结果为true，为什么呢？ -1 is lessthan to 0是真的。

我要做的是，我在上方插入了If statement..和If runs < 0 then ....，Exit Sub以立即结束语句。如果您向-1输入Input Text，则结果是这样的，如果runs(-1)小于0，则布尔结果为true，则它将继续进行声明，即Message和Exit Sub。

尝试上面的代码，并使用断点。.希望这对您有所帮助。

“运行”功能存在问题

1 个答案: