vb.net dll反射事件

Question

我正在尝试将用户定义的事件参数类从 dll 传递到我的主程序。两者都定义了事件参数类，但是当我尝试将事件委托绑定到方法时，它不会绑定，因为它的签名不兼容。我已将代码剥离到主要问题。

dll 中的代码引发一个名为 ValueChange 的事件，其参数为 ValueEventArgs：

Public Class Main
  Public Event ValueChange(ByVal sender As System.Object, ByVal e As ValueEventArgs)
  Private _Value As Integer

  Public Sub Up()
    _Value += 1
    RaiseEvent ValueChange(Me, New ValueEventArgs(_Value))
  End Sub
End Class

Public Class ValueEventArgs
  Inherits System.EventArgs
  Public Property Value As Integer

  Public Sub New(ByVal Value As Integer)
    Me.Value = Value
  End Sub
End Class

Main 程序加载 dll 并将事件委托绑定到方法 ShowValue：

Imports System.Reflection

Public Class Main
  Private DriverAssembly As [Assembly]
  Private DriverClass As Type
  Private DriverClassInstance As Object

  Private Sub ButtonLoad_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonLoad.Click
    DriverAssembly = [Assembly].Load("reflection_event, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")
    DriverClass = DriverAssembly.GetType("ReflectionEventDll.Main")
    DriverClassInstance = Activator.CreateInstance(DriverClass)

    ' get the handler method
    Dim Method As MethodInfo = Me.GetType.GetMethod("ShowValue")

    ' get the event and create a delegate
    Dim ValueChangeEvent As EventInfo = DriverClass.GetEvent("ValueChange")
    Dim Handler As [Delegate] = [Delegate].CreateDelegate(ValueChangeEvent.EventHandlerType, Me, Method) ' Fails
    ' Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type.

    ' add the event handler
    ValueChangeEvent.AddEventHandler(DriverClassInstance, Handler)
  End Sub

  Private Sub ButtonUp_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonUp.Click
    DriverClass.GetMethod("Up").Invoke(DriverClassInstance, Nothing) ' invoke the method on the driver class instance
  End Sub

  Public Sub ShowValue(ByVal sender As Object, ByVal e As ValueEventArgs)
    MessageBox.Show(e.Value.ToString())
  End Sub
End Class

Public Class ValueEventArgs
  Inherits System.EventArgs
  Public Property Value As Integer

  Public Sub New(ByVal Value As Integer)
    Me.Value = Value
  End Sub
End Class

如果我删除委托和 AddEventHandler 的创建，一切正常，当然没有事件。

有趣的是，如果我在主程序中更改 ShowValue 方法的参数，一切都会突然起作用，包括事件。

Public Sub ShowValue(ByVal sender As Object, ByVal e As EventArgs)
  ' works, but the Value is lost
End Sub

它变得更好，因为它没有完全丢失。如果我在 Sub 上放置一个断点，我可以看到 e 包含一个名为 Value 的属性。
DirectCast 也会失败，但将 EventArgs 写入对象似乎可行。

  Public Sub ShowValue(ByVal sender As Object, ByVal e As EventArgs)
    Dim Obj As Object = e
    MessageBox.Show(Obj.Value.ToString())
  End Sub

它有效，但我认为这不是正确的方法。在处理来自 dll 的事件时，如何使用用户定义的事件参数类？

Answer 1

在this answer 的帮助下，我找到了解决方案。我觉得这是目前最好的解决方案，如果失败，它会产生可用的错误。

dll 中的代码和方法的绑定保持不变，但是被调用的方法现在使用反射来获取 Value 属性。移植到 VB.net 的方法如下所示：

  Public Sub ShowValue(ByVal sender As Object, ByVal e As EventArgs)
    Dim ValueProperty As PropertyInfo = e.GetType().GetProperty("Value")
    Dim Value As Integer = Convert.ToInt32(ValueProperty.GetValue(e, Nothing))

    MessageBox.Show(Value.ToString())
  End Sub