StickyLabel是什么？为何出现在ContextMenuStrip集合及类型转换异常问题

为什么会出现StickyLabel转换错误？ #

首先，你的核心问题是遍历了错误的集合：ContextMenuStrip.Controls是用于存放上下文菜单容器内的辅助子控件，而非你手动添加的菜单项目（ToolStripMenuItem/ToolStripSeparator）。

那个StickyLabel是Microsoft Office/VSTO框架内部的一个辅助控件，通常用于在Office界面中显示临时提示或状态文本，会被VSTO自动注入到上下文菜单的控件集合中，不属于你定义的菜单项目，所以当你尝试把它强制转换为ToolStripItem时就会抛出类型转换异常。

你应该遍历的是ContextMenuStrip.Items集合——这个集合专门用于存储所有的菜单项目（也就是你添加的ToolStripMenuItem和ToolStripSeparator）。

修复后的代码 #

把循环对象从Controls改为Items，同时优化选中状态的判断逻辑，减少重复代码：

Private Sub ContextMenuStrip_PopulatedItems_Opening(sender As Object, e As CancelEventArgs) Handles ContextMenuStrip_PopulatedItems.Opening
    Dim ThisListView As ListView = TryCast(ContextMenuStrip_PopulatedItems.SourceControl, ListView)
    If ThisListView Is Nothing Then Return ' 额外判断，避免SourceControl不是ListView的情况

    Dim selectedCount As Integer = ThisListView.SelectedItems.Count
    Dim hasSelection As Boolean = selectedCount > 0
    Dim isSingleSelection As Boolean = selectedCount = 1
    Dim isMultipleSelection As Boolean = selectedCount > 1

    For Each MyControl As ToolStripItem In ContextMenuStrip_PopulatedItems.Items
        MyControl.Visible = False
        Dim tagValue As String = TryCast(MyControl.Tag, String)
        
        If String.IsNullOrEmpty(tagValue) Then
            ' 可根据需求选择隐藏或抛出异常，这里默认跳过
            Continue For
            ' Throw New ApplicationException("The control tag property is not set or invalid.")
        End If

        Select Case tagValue
            Case "ShowAlways"
                MyControl.Visible = True
            Case "WhenSelection"
                MyControl.Visible = hasSelection
            Case "WhenSingleSelection"
                MyControl.Visible = isSingleSelection
            Case "WhenMultipleSelection"
                MyControl.Visible = isMultipleSelection
            Case Else
                Throw New ApplicationException($"Unrecognized tag value: {tagValue}")
        End Select
    Next
End Sub

额外优化点 #

1. 用TryCast替代直接强制转换SourceControl，避免上下文菜单被其他控件触发时出现异常
2. 提前计算选中状态变量，减少重复访问SelectedItems.Count的次数，让代码更清晰
3. 增加对Tag为空或非字符串类型的判断，避免出现额外的转换异常

内容的提问来源于stack exchange，提问作者Ama