我正在开发一个系统，我计划使用RealProxy对象启用对一组对象的拦截方法调用，处理调用，然后返回适当的结果。
这可以找到简单的返回类型，如字符串或整数，但我似乎无法从RealProxy.Invoke方法返回对象。
一切正常。我没有错误，但返回的值总是NOTHING，而不是对象。
我已经编写了尽可能最小的示例代码，并将其包含在下面。
基本上，只需调用RPtest并单步执行即可。 该代码创建一个简单的对象RPTestA，其中包含字符串字段和对象值字段 然后它检索字符串 Dim x = c.Name 哪个工作正常 然后尝试检索对象
Dim r = c.SubObj
总是什么都不返回。
但是，在FieldGetter例程中，此代码为：
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
似乎工作正常，将ReturnMessage的ReturnValue字段设置为上面的Activator.CreateInstance（t）调用创建的对象。
我怀疑它是某种序列化的东西，但我不知所措。
您应该可以立即运行此代码，但只需将其粘贴到新的VB.net项目中即可。
'----------------------------------------------------------------------------
Imports System.Security.Permissions
Imports System.Diagnostics
Imports System.Reflection
Imports System.Runtime.CompilerServices
Imports System.Runtime.Serialization
Imports System.Runtime.Remoting
Imports System.Runtime.Remoting.Activation
Imports System.Runtime.Remoting.Messaging
Imports System.Runtime.Remoting.Proxies
Public Module RPTest
Public Sub RPTest()
'---- create a new object that is automatically proxied
' See the RPProxyAttribute for details
Dim c = New RPTestA
Dim x = c.Name
'x is returned as a string value just fine
Dim r = c.SubObj
'********* PROBLEM IS HERE, r ends up nothing
End Sub
End Module
'ROOT test object
Public Class RPTestA
Inherits RPBase
Public Name As String = "Test Name"
Public SubObj As RPTestB
End Class
'SUB OBJECT which should be returned as a field value from the root object above
Public Class RPTestB
Inherits RPBase
Public SubProperty As String = "SubObj Test Property"
End Class
''' <summary>
''' Base proxyable object class
''' </summary>
''' <remarks></remarks>
<RPProxy()> _
Public MustInherit Class RPBase
Inherits ContextBoundObject
End Class
<PermissionSet(SecurityAction.Demand, Name:="FullTrust")> _
Public Class RPProxy
Inherits RealProxy
Private m_target As MarshalByRefObject
Public Sub New()
m_target = DirectCast(Activator.CreateInstance(GetType(ConfigRP)), MarshalByRefObject)
Dim myObjRef = RemotingServices.Marshal(m_target)
End Sub
Public Sub New(ByVal classToProxy As Type)
MyBase.New(classToProxy)
End Sub
Public Sub New(ByVal ClassToProxy As Type, ByVal targetObject As MarshalByRefObject)
m_target = targetObject
Dim myObjRef = RemotingServices.Marshal(m_target)
End Sub
Public Overrides Function Invoke(ByVal msg As IMessage) As IMessage
Dim returnMsg As IMethodReturnMessage = Nothing
If TypeOf msg Is IConstructionCallMessage Then
'---- handle constructor calls
Dim ConstructionCallMessage = DirectCast(msg, IConstructionCallMessage)
returnMsg = InitializeServerObject(ConstructionCallMessage)
Me.m_target = Me.GetUnwrappedServer()
SetStubData(Me, Me.m_target)
Return returnMsg
ElseIf TypeOf msg Is IMethodCallMessage Then
'---- handle all other method calls
Dim methodCallMessage = DirectCast(msg, IMethodCallMessage)
'---- before message processing
preprocess(methodCallMessage)
'---- execute the method call
Dim rawReturnMessage = RemotingServices.ExecuteMessage(Me.m_target, methodCallMessage)
'---- and postprocess
returnMsg = postprocess(methodCallMessage, rawReturnMessage)
Else
Throw New NotSupportedException()
End If
Return returnMsg
End Function
'Called BEFORE the actual method is invoked
Private Sub PreProcess(ByVal msg As IMessage)
Console.WriteLine("before method call...")
End Sub
'Called AFTER the actual method is invoked
Private Function PostProcess(ByVal Msg As IMethodCallMessage, ByVal msgReturn As ReturnMessage) As ReturnMessage
Dim r As ReturnMessage
If Msg.MethodName = "FieldGetter" Then
r = FieldGetter(Msg, msgReturn)
ElseIf Msg.MethodName = "FieldSetter" Then
'na
r = msgReturn
ElseIf Msg.MethodName.StartsWith("get_") Then
'na
r = msgReturn
ElseIf Msg.MethodName.StartsWith("set_") Then
'na
r = msgReturn
Else
r = msgReturn
End If
Return r
End Function
Private Function FieldGetter(ByVal Msg As IMethodCallMessage, ByVal msgReturn As IMethodReturnMessage) As IMethodReturnMessage
Dim t = Me.Target.GetType
'---- This retrieves the type of the field that the getter should retrieve
t = t.GetField(Msg.InArgs(1), BindingFlags.Instance Or BindingFlags.Public).FieldType
If t.Name = "String" Then
'---- just return what the object returned as a result of ExecuteMessage
Return msgReturn
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
Else
Return msgReturn
End If
End Function
Public Property Target() As Object
Get
Return Me.m_target
End Get
Set(ByVal value As Object)
Me.m_target = value
End Set
End Property
End Class
<AttributeUsage(AttributeTargets.Class)> _
<SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.Infrastructure)> _
Public Class RPProxyAttribute
Inherits ProxyAttribute
Public Overrides Function CreateInstance(ByVal Type As Type) As MarshalByRefObject
Dim proxy = New RPProxy(Type)
Dim transparentProxy = DirectCast(proxy.GetTransparentProxy(), MarshalByRefObject)
Return transparentProxy
End Function
End Class
答案 0 :(得分：3)
嗯，事实证明，这是一个非常简单的解决方案，一旦你工作过了神奇的ReturnMessage构造函数，这是非常误导的！
非常感谢我的一位老同事Rich Quackenbush花了几分钟时间来检查这一点。有时候，你无法看到森林中的树木！
无论如何，在FieldGetter中，我正在做这个
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
似乎完全合理，新创建的对象被传递给名为ReturnValue的ReturnMessage构造函数参数。
但不是。实际上你必须创建一个对象数组并将其作为该数组中的3个元素传递，如下所示：
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg) '---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(Nothing, New Object() {Nothing, Nothing, o}, 3, mc.LogicalCallContext, mc)
Return r
事实证明，这是因为FieldGetter函数被代理“调用”并截获，它的签名是
FieldGetter(StringtypeName,StringfieldName,Object&val)
其中，为了为该调用构造ReturnMessage，意味着它根本没有Returnvalue，而是返回值作为该列表中的第3个参数返回。
因为我实际上并没有调用真正的FieldGetter函数，所以前两个参数（typename和fieldname）是无关紧要的，但是第3个参数是放置返回值的适当位置。
后见之明总是显而易见的！
非常感谢Rich。