在没有无限循环的情况下管理“CheckBox_Checked”事件

Question

我知道这看起来很容易解决，但我遇到了麻烦。我有一个CheckBox，选中后，我删除了我的Windows Form 上的DataGridView 的数据源，并删除了一些ReadOnly 的ReadOnly 属性。

我知道CheckedChanged 事件会将我的代码发送到无限循环中，但如果不每次都更改CheckedState，我无法确定哪个事件会处理此更改。我尝试过使用Click、MouseClick 和CheckStateChanged 事件，但没有成功。

这是我当前的代码：

Private Sub chkManual_MouseClick(sender As Object, e As EventArgs) Handles chkManual.MouseClick

        If Not Me.chkManual.Checked Then
        Me.chkManual.Checked = False
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = True
        Me.txtCasenum.ReadOnly = True
        Me.txtCommnum.ReadOnly = True

        Exit Sub

   Else
        Me.dgDataEntry.DataSource = Nothing
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = False
        Me.txtCasenum.ReadOnly = False
        Me.txtCommnum.ReadOnly = False
        ClearForm()

        frmPDF.Hide()
        Exit Sub
    End If
    End Sub

CheckBox 的属性：AutoCheck = True、Checked = False 和 CheckState = Unchecked

我已经研究过这些：

CheckBox_Checked event

Is there a simpler way to process check boxes?

CheckBox reverts to checked after being unchecked

How to check if a checkboxes state has changed

How can I prevent an assignment statement to CheckBox.Checked from raising the CheckChanged event?

http://www.vbforums.com/showthread.php?758455-CheckBox-code-got-stuck-in-an-infinite-loop-can-not-unchecked-it

编辑

如果您的ClearForm() 子不会每次都将CheckBox 的CheckedState 更改回False，这会有所帮助。感谢@Visual Vincent 指出显而易见的事情。代码没什么问题，把EventHandler改成CheckedChanged

最终代码（就这么简单）：

Private Sub chkManual_CheckedChanged(sender As Object, e As EventArgs) Handles chkManual.CheckedChanged
    If Me.chkManual.Checked Then
        Me.dgDataEntry.DataSource = Nothing
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = False
        Me.txtCasenum.ReadOnly = False
        Me.txtCommnum.ReadOnly = False

        ClearForm()
        frmPDF.Hide()
    Else
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = True
        Me.txtCasenum.ReadOnly = True
        Me.txtCommnum.ReadOnly = True
    End If
End Sub

Answer 1

您可以删除更改复选框状态的代码吗？例如：

Me.chkManual.Checked = False

该框将选中或取消选中，而无需您的代码执行此操作，并且该事件只会抛出一次。

Answer 2

我认为最简单的方法是在处理复选框选中状态之前删除事件侦听器。使用 try-finally 块来确保复选框事件监听器总是被设置回来。

Try
RemoveHandler chkManual AddressOf chkManual_MouseClick
Me.chkManual.Checked = False
...
Finally
AddHandler chkManual AddressOf chkManual_MouseClick
End Try

Answer 3

我不确定您是否希望 CheckBox 在选中时自动再次取消选中！？...看起来像一个奇怪的界面。

无论如何，如果您希望在 Check 状态更改时发生某些事情：

Private Sub chkManual_CheckedChanged(sender As Object, e As EventArgs) Handles chkManual.CheckedChanged
    If chkManual.Checked Then
        Debug.Print("Checked")
        Me.dgDataEntry.DataSource = Nothing
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = False
        Me.txtCasenum.ReadOnly = False
        Me.txtCommnum.ReadOnly = False
        ClearForm()

        frmPDF.Hide()
    Else
        Debug.Print("UnChecked")
        Me.cbRegion.SelectedIndex = -1

        Me.txtIssueDate.ReadOnly = True
        Me.txtCasenum.ReadOnly = True
        Me.txtCommnum.ReadOnly = True
    End If
End Sub

您可以像这样在没有无限循环的情况下取消选中该复选框：

Private Sub chkManual_CheckedChanged(sender As Object, e As EventArgs) Handles chkManual.CheckedChanged
    Static counter As Integer
    If chkManual.Checked Then
        counter = counter + 1 ' just to show we're not in an infinite loop...
        Debug.Print("Checked " & counter) ' just to show we're not in an infinite loop...
        chkManual.Checked = False
    Else
        Debug.Print("UnChecked")
    End If
End Sub

不知道你为什么要这样做...似乎这基本上是一个“重置”按钮，因为它不能保持选中状态...