与表单事件相关的"无法使用已与其基础 RCW 分离的 COM 对象 vb.net"错误

Question

我正在将 arcobjects 映射事件挂接到 vb.net 窗体以侦听地图选择更改。这一切都工作正常，但用户在打开表单时偶尔会报告此错误。我看不到任何模式来重现错误，而且似乎是随机的。

"无法使用已与其基础 RCW 分离的 COM 对象">

它起源于我钩接事件的Load((方法形式。

谁能帮助我了解我做错了什么？我正在 FormClosesing(( 事件中解开地图选择事件，我认为这是正确的方法。

Public Class MyForm
Private _activeViewEvents As IActiveViewEvents_Event
Private Sub FormLoad(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
_activeViewEvents = TryCast(pMxDoc.ActiveView.FocusMap, IActiveViewEvents_Event)
AddHandler _activeViewEvents.SelectionChanged, AddressOf SelectionChanged    
End Sub
Private Sub SelectionChanged
'do something when selection is changed
End Sub
Private Sub FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
RemoveHandler _activeViewEvents.SelectionChanged, AddressOf SelectionChanged
End Sub
End Class

Answer 1

您创建和销毁处理程序的方法有效。在表单打开时更改地图文档时，您可能会收到 RCW COM 异常。由于您正在使用FocusMap来创建句柄，因此当文档更改时，FocusMap也会更改，这意味着您需要为新地图文档重新创建处理程序。

Answer 2

好的，所以我想我已经通过使用 ActiveViewChanged 事件解决了这个问题。我没有在每个表单加载或新文档事件上重新挂钩事件，而是尝试侦听何时触发 ActiveViewChanged 事件，并每次重新挂钩 SelectionChanged 事件。事实证明，每次打开新文档时都会多次触发此操作(不确定原因(。无论如何，问题似乎已经消失了。下面是一些示例代码：

Public Class MyForm
Private _activeViewEvents As IActiveViewEvents_Event
Private _docEvents As IDocumentEvents_Event
Private Sub FormLoad(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
AddHandler _docEvents.ActiveViewChanged, AddressOf ActiveViewChanged
End Sub
Private Sub ActiveViewChanged()
Dim maps = pMxDoc.Maps
For i = 0 to maps.Count - 1 'remove handlers from all maps
RemoveActiveViewEvents(maps.Item(i))
Next
SetupActiveViewEvent(pMxDoc.ActiveView.FocusMap) 'only add handler to active map
End Sub
Private Sub RemoveActiveViewEvents(map As IMap)
_activeViewEvents = CType(map, IActiveViewEvents_Event)
RemoveHandler _activeViewEvents.SelectionChanged, AddressOf SelectionChanged
End Sub
Private Sub SetupActiveViewEvents(map As IMap)
_activeViewEvents = CType(map, IActiveViewEvents_Event)
AddHandler _activeViewEvents.SelectionChanged, AddressOf SelectionChanged
End Sub
Private Sub SelectionChanged
'do something when selection is changed
End Sub
End Class