非托管代码调用vb.net回调 [英] Unmanaged code calling vb.net callback

问题描述

我正在将处理COM对象（可能用VB6编写）的事件的vb.net应用程序从框架1.1升级到WPF 2.0 / 3.5

I am upgrading vb.net app that handles the events of a COM object (possibly written in VB6) from framework 1.1 to WPF 2.0/3.5

代码： （为简便起见，简化了对象名称）

The code: (object names simplified for brevity)

public class MyClass
   Private WithEvents serviceMonitor As COMOBJECT.ServiceMonitor

   Public Sub New()
       serviceMonitor = New COMOBJECT.ServiceMonitor()
       serviceMonitor.Connect([some ip address])
   End Sub

   Private Sub ServiceMonitor_ServiceConnectionUp(ByVal MonitorId As Integer, ByVal UserArg As Integer) _ 
        Handles serviceMonitor.ServiceConnectionUp

        Debug.WriteLine("connection up!")
   End Sub

    ' other similar handlers omitted
End Class

应用程序将以是预期的，但是在几秒钟之内，我就会出现访问冲突。尽管基本运行良好，但基本的回调代码类似于.net 1.1版本。

The app will get the callbacks as expected, however within a few seconds I get an Access Violation. The basic callback code is similar to the .net 1.1 version although it ran perfectly.

根据我对错误的研究，这是由垃圾收集器移动东西引起的。由于我没有将任何要处理的对象传递给DLL，所以我猜想回调是问题所在。其他人通过使用< UnmanagedFunctionPointer（CallingConvention.Cdecl）> 和/或Marshal.GetFunctionPointerForDelegate的委托来解决此问题。

According to my research on the error, it is caused by the garbage collector moving things around. Since I am not passing the DLL any objects to manipulate, I am guessing that the callbacks are the issues. Other folks have solved this via a delegate with <UnmanagedFunctionPointer(CallingConvention.Cdecl)> and/or Marshal.GetFunctionPointerForDelegate.

不幸的是，我发现的所有示例都是DLL具有某种SetCallback（IntPtr）方法的情况。我正在使用WithEvents和Handles关键字。这是我的尝试（请注意，我删除了Handles关键字，以便可以使用AddHandler：

Unfortunately, all the examples I have found are cases where the DLL has some sort of SetCallback(IntPtr) method. I am using WithEvents and the Handles keyword. Here is my attempt (note that I removed the Handles keyword so that I can use AddHandler:

<UnmanagedFunctionPointer(CallingConvention.Cdecl)> _
   Delegate Sub ServiceMonitor_ServiceConnectionUpDelegate(ByVal MonitorId As Integer, ByVal UserArg As Integer)

public class MyClass
   Private WithEvents serviceMonitor As COMOBJECT.ServiceMonitor

   Public Sub New()
       serviceMonitor = New COMOBJECT.ServiceMonitor()
       del = New ServiceMonitor_ServiceConnectionUpDelegate(AddressOf ServiceMonitor_ServiceConnectionUp)
       AddHandler serviceMonitor.ServiceConnectionUp, del ' <--- Error here
       serviceMonitor.Connect([some ip address])
   End Sub

   Private Sub ServiceMonitor_ServiceConnectionUp(ByVal MonitorId As Integer, ByVal UserArg As Integer) 

        Debug.WriteLine("connection up!")
    End Sub

    ' other similar handlers omitted
End Class

我在AddHandler行上遇到的错误是： Value of类型MyClass.ServiceMonitor_ServiceConnectionUpDelegate无法转换为COMOBJECT._IServiceMonitorEvents_ServiceConnectionUpEventHandler

The error I am getting on the AddHandler line is: "Value of type MyClass.ServiceMonitor_ServiceConnectionUpDelegate cannot be converted to COMOBJECT._IServiceMonitorEvents_ServiceConnectionUpEventHandler"

当我将鼠标悬停在上述事件处理程序上时，其签名为：
代表Sub _IServiceMonitorEvents_ServiceConnectionUpEventHandler（ByVal MonitorId为整数，ByVal UserArg为整数）

When I mouse hover the mentioned Event Handler it has a signature of: Delegate Sub _IServiceMonitorEvents_ServiceConnectionUpEventHandler(ByVal MonitorId As Integer, ByVal UserArg As Integer)

签名是相同的，所以我不确定问题出在哪里。

The signatures are identical so I'm not sure what the problem is.

问题1：如何以这种方式在AddHandler中使用委托？
问题2：是否需要涉及 Marshal.GetFunctionPointerForDelegate（）吗？

Question 1: How do I use a delegate with AddHandler in this fashion? Question 2: Does Marshal.GetFunctionPointerForDelegate() need to be involved? It returns an IntPtr but AddHandler wants a delegate.

预先感谢。

推荐答案

尽管我还不能100％地确定问题已得到解决，但是到目前为止，我还没有任何访问冲突。

Although I am not yet 100% certain that the issue is fixed, so far I haven't had any more access violations.

基本上，我删除了WithEvents关键字，以防止VB使用其自己的COM-> .net错误处理，而是使用库中用于C ++客户端的方法。我使用了< UnmanagedFunctionPointer（CallingConvention.Cdecl）> 并将库传递给 Marshal.GetFunctionPointerForDelegate IntPtr。我还保留了对IntPtr的引用，尽管它可能已被矫kill过正。

Basically I removed the WithEvents keyword to prevent VB from using its own COM -> .net error handling and instead used the methods in the library intended for C++ clients. I used the <UnmanagedFunctionPointer(CallingConvention.Cdecl)> and passed the library a Marshal.GetFunctionPointerForDelegate IntPtr. I also kept a reference to the IntPtr althought it may have been overkill.

我很困惑，因为WithEvents处理程序在.net中工作得很好，我不得不经历所有这些事情。 1.1。主要区别在于我使用的是表单而不是类来处理回调。

I am confused that I had to go through all this since the WithEvents handlers worked perfectly in .net 1.1. The main differences was that I used a form to handle the callbacks rather than a class.

一个挥之不去的问题是，当我关闭应用程序时，调试器有时仍会运行形成。我希望这只是一个调试器怪癖。

One lingering issue is the fact that the debugger sometimes stays running when I close the apps form. I am hoping it is just a debugger quirk.

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