VB - 按下退格键后，TextChanged 没有正确触发？

Question

我的问题归结为：

我有六个文本框，它们期望一个介于 0 和给定数字之间的值。我想要实现的是：

• 如果输入的数字介于 0 和指定数字之间（作为标签），文本将保持黑色
• 如果输入的数字超过指定的数字，文本将变为红色

这里的问题是，如果指定的数字是“10”，而用户输入 11，它会变成红色，这是应该的，但是，如果他们按下退格键（输入的数字现在是 1），数字仍然是红色的，即不是预期的功能 - 数字 1 应该是黑色的，因为它介于 0 和指定的数字之间。

所有指定的数字现在都是硬编码的（我正在学习初学者课程，这只是我为了增加程序功能而做的事情，我还没有为每个“作业”添加类" ) 并且您可以在技术上输入负数，我目前不在乎。

这是作为特定 GroupBox 中所有文本框的处理程序添加的子例程

' Handler which gets added to all TextBoxes in "grpGrades" GroupBox
    Private Sub txtGradePoints_TextChanged(sender As Object, e As EventArgs)

        ' Take in generic sender (Textbox) and convert to TextBox (necessary due to Strict mode)
        Dim textBox = CType(sender, TextBox)
        Try
            ' the value of the current TextBox being checked
            Dim val = Decimal.Parse(textBox.Text)
            Select Case textBox.Name
                Case "txtPostPoints"
                    If val > 10 Then textBox.ForeColor = Color.Red
                Case "txtCh1TestPoints", "txtCh2TestPoints", "txtCh3TestPoints"
                    If val > 50 Then textBox.ForeColor = Color.Red
                Case "txtCh2TutPoints", "txtCh3TutPoints"
                    If val > 25 Then textBox.ForeColor = Color.Red
                Case Else
                    textBox.ForeColor = Color.Black

            End Select
        Catch
            textBox.ForeColor = SystemColors.ControlText
        End Try


    End Sub

这是 onLoad 处理程序，它从“grpGrades”GroupBox 获取适当的 TextBox 控件，并将上述 TextChanged 处理程序添加到每个控件。

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        ' Get array of TextBox Controls from the "grpGrades" GroupBox
        Dim textBoxes = grpGrades.Controls.OfType(Of TextBox)()

        ' Go through the array of TextBoxes and add the TextChanged handler to each TextChanged event
        For Each txt In textBoxes
            AddHandler txt.TextChanged, AddressOf txtGradePoints_TextChanged
        Next

        'AddHandler txtPostPoints.TextChanged, AddressOf txtGradePoints_TextChanged
        'AddHandler txtCh1TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
        'AddHandler txtCh2TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
        'AddHandler txtCh3TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
        'AddHandler txtCh2TutPoints.TextChanged, AddressOf txtGradePoints_TextChanged
        'AddHandler txtCh3TutPoints.TextChanged, AddressOf txtGradePoints_TextChanged
    End Sub

子程序的最后一部分只是注释掉的代码，也是我最初添加处理程序的方式，以防万一我的新方法出现问题。

编辑：是否有必要拒绝投票？是什么原因？

Answer 1

您的代码从不测试有效值。当当前文本框返回有效值时，将当前文本框设置为黑色的 Case Else 永远不会被命中。这不会发生，因为 Select Case 将匹配文本框的当前 Name，将再次测试无效值，然后退出 Select Case 块。您需要为当前文本框名称的适当大小写中的有效值设置颜色。该IF条件运算符可以一切减少到单行

Private Sub txtGradePoints_TextChanged(sender As Object, e As EventArgs)

    ' Take in generic sender (Textbox) and convert to TextBox (necessary due to Strict mode)
    Dim textBox = CType(sender, TextBox)
    Try
        ' the value of the current TextBox being checked
        Dim val = Decimal.Parse(textBox.Text)
        Select Case textBox.Name
            Case "txtPostPoints"
                textBox.ForeColor = IF(val > 10, Color.Red, Color.Black)
            Case "txtCh1TestPoints", "txtCh2TestPoints", "txtCh3TestPoints"
                textBox.ForeColor = IF(val > 50, Color.Red, Color.Black)
            Case "txtCh2TutPoints", "txtCh3TutPoints"
                textBox.ForeColor = IF(val > 25, Color.Red, Color.Black)
            Case Else
                ' Not sure if it is needed for other textboxes....
                textBox.ForeColor = Color.Black

        End Select
    Catch
        textBox.ForeColor = SystemColors.ControlText
    End Try


End Sub