Cannot remove .NET event handler

XDSoft

问题：

When my AddIn is loaded it starts listening to the DocumentToBeDestroyed event and it works fine.

However, when later on I try to stop listening to this event I do not succeed and so my handler keeps getting called.

Is there a solution for this?

Here is my code:

1. Imports Autodesk.AutoCAD.Runtime
   
2. Imports Autodesk.AutoCAD.ApplicationServices
   
3. 
   
4. Public Class Commands
   
5.   Implements IExtensionApplication
   
6. 
   
7.   Public Sub Initialize() Implements IExtensionApplication.Initialize
   
8.     AddHandler Application.DocumentManager.DocumentToBeDestroyed, AddressOf docBeginDocClose
   
9.   End Sub
   
10. 
    
11.   Public Sub Terminate() Implements IExtensionApplication.Terminate
    
12.   End Sub
    
13. 
    
14.   Public Sub docBeginDocClose(ByVal senderObj As Object, _
    
15.                               ByVal docColDocActEvtArgs As DocumentCollectionEventArgs)
    
16.     System.Diagnostics.Debug.Print("in docBeginDocClose")
    
17.   End Sub
    
18. 
    
19.   <CommandMethod("StopEvent")> _
    
20.   Public Sub StopEvents()
    
21.     Try
    
22.       RemoveHandler Application.DocumentManager.DocumentToBeDestroyed, AddressOf docBeginDocClose
    
23.     Catch ex As Exception
    
24.       MsgBox("Error: " & ex.Message)
    
25.     End Try
    
26.   End Sub
    
27. 
    
28. End Class
    

Imports Autodesk.AutoCAD.Runtime<br /> Imports Autodesk.AutoCAD.ApplicationServices<br /> <br /> Public Class Commands<br />   Implements IExtensionApplication<br /> <br />   Public Sub Initialize() Implements IExtensionApplication.Initialize<br />     AddHandler Application.DocumentManager.DocumentToBeDestroyed, AddressOf docBeginDocClose<br />   End Sub<br /> <br />   Public Sub Terminate() Implements IExtensionApplication.Terminate<br />   End Sub<br /> <br />   Public Sub docBeginDocClose(ByVal senderObj As Object, _<br />                               ByVal docColDocActEvtArgs As DocumentCollectionEventArgs)<br />     System.Diagnostics.Debug.Print("in docBeginDocClose")<br />   End Sub<br /> <br />   <CommandMethod("StopEvent")> _<br />   Public Sub StopEvents()<br />     Try<br />       RemoveHandler Application.DocumentManager.DocumentToBeDestroyed, AddressOf docBeginDocClose<br />     Catch ex As Exception<br />       MsgBox("Error: " & ex.Message)<br />     End Try<br />   End Sub<br /> <br /> End Class<br />

解答：

AutoCAD creates an instance of the class that contains the Initialize() function. If the command function is an instance function (not static/shared), then AutoCAD also creates a new instance of the class that contains that function for each document. If the handler is an instance function as well, then you'll get the instance of it that belongs to the same class instance as the command handler.

So you attach one instance’s function to the event inside Initialize() or a command, then you try to remove another instance’s function later on – so you do not remove the function that you attached to the event in the first place.

That’s why your handler keeps being called even after you tried to remove it.

So the solution is to simply make the function static/shared:

Public Shared Sub docBeginDocClose(ByVal senderObj As Object, _
                              ByVal docColDocActEvtArgs As DocumentCollectionEventArgs)
  System.Diagnostics.Debug.Print("in docBeginDocClose")
End Sub