c# - 帮助将小型 C# WCF 应用程序转换为 Visual Basic(第 2 部分)

Question

我最近问了一个关于将我在互联网上找到的代码示例从 C# 翻译成 VB 的问题，我得到了自动代码翻译网站的链接 (http://converter.telerik.com/& http://www.developerfusion.com/tools/convert/csharp-to-vb/ ) .我是 VB 的新手，不幸的是，翻译人员返回的 VB 无法在 Visual Studio 2010 中编译。我希望有人可以帮助我修复 VB 代码的非工作部分。

这是我要转换成 VB 的 C# 代码:

namespace WCFCallbacks
{
    using System;
    using System.ServiceModel;

    [ServiceContract(CallbackContract = typeof(IMessageCallback))]
    public interface IMessage
    {
        [OperationContract]
        void AddMessage(string message);

        [OperationContract]
        bool Subscribe();

        [OperationContract]
        bool Unsubscribe();
    }

    interface IMessageCallback
    {
        [OperationContract(IsOneWay = true)]
        void OnMessageAdded(string message, DateTime timestamp);
    }        
}

namespace WCFCallbacks
{
    using System;
    using System.Collections.Generic;
    using System.ServiceModel;

    public class MessageService : IMessage
    {
        private static readonly List<IMessageCallback> subscribers = new List<IMessageCallback>();

        public void AddMessage(string message)
        {

            subscribers.ForEach(delegate(IMessageCallback callback)
            {
                if (((ICommunicationObject)callback).State == CommunicationState.Opened)
                {
                    callback.OnMessageAdded(message, DateTime.Now);
                }
                else
                {
                    subscribers.Remove(callback);
                }
            });
        }

        public bool Subscribe()
        {
            try
            {
                IMessageCallback callback = OperationContext.Current.GetCallbackChannel<IMessageCallback>();
                if (!subscribers.Contains(callback))
                    subscribers.Add(callback);
                return true;
            }
            catch
            {
                return false;
            }
        }

        public bool Unsubscribe()
        {
            try
            {
                IMessageCallback callback = OperationContext.Current.GetCallbackChannel<IMessageCallback>();
                if (!subscribers.Contains(callback))
                    subscribers.Remove(callback);
                return true;
            }
            catch
            {
                return false;
            }
        }
    }
}

我上面列出的两个转换器都返回相同的 VB 代码。不起作用的 VB 代码部分在 AddMessage 方法中。这是翻译器生成的 VB 代码:

Imports System.ServiceModel

Namespace WCFCallbacks

    <ServiceContract(CallbackContract:=GetType(IMessageCallback))> _
    Public Interface IMessage
        <OperationContract()> _
        Sub AddMessage(ByVal message As String)

        <OperationContract()> _
        Function Subscribe() As Boolean

        <OperationContract()> _
        Function Unsubscribe() As Boolean
    End Interface

    Interface IMessageCallback
        <OperationContract(IsOneWay:=True)> _
        Sub OnMessageAdded(ByVal message As String, ByVal timestamp As DateTime)
    End Interface

End Namespace

Imports System
Imports System.Collections.Generic
Imports System.ServiceModel

Namespace WCFCallbacks

    Public Class MessageService
        Implements IMessage

        Private Shared ReadOnly subscribers As New List(Of IMessageCallback)()

        Public Sub AddMessage(ByVal message As String) Implements IMessage.AddMessage

   subscribers.ForEach(Function(callback As IMessageCallback) Do
            If DirectCast(callback, ICommunicationObject).State = CommunicationState.Opened Then
                callback.OnMessageAdded(message, DateTime.Now)
            Else
                subscribers.Remove(callback)
            End If
   End Function)
  End Sub

        Public Function Subscribe() As Boolean Implements IMessage.Subscribe
            Try
                Dim callback As IMessageCallback = OperationContext.Current.GetCallbackChannel(Of IMessageCallback)()
                If Not subscribers.Contains(callback) Then
                    subscribers.Add(callback)
                End If
                Return True
            Catch
                Return False
            End Try
        End Function

        Public Function Unsubscribe() As Boolean Implements IMessage.Unsubscribe
            Try
                Dim callback As IMessageCallback = OperationContext.Current.GetCallbackChannel(Of IMessageCallback)()
                If Not subscribers.Contains(callback) Then
                    subscribers.Remove(callback)
                End If
                Return True
            Catch
                Return False
            End Try
        End Function

    End Class

End Namespace

---

如果有人可以帮助我修复 AddMessage 方法的 VB 代码，我将不胜感激。谢谢!

Answer 1

我不是 VB.NET 程序员，但我认为 C# -> VB.NET 解析器显然无法处理该委托(delegate)技巧。代码中发生的事情实际上是非常基本的，如果你用委托(delegate)去除了那层复杂性(只有当你完全理解它时才看起来很简单)。最后，C# 代码只是遍历订阅者列表并调用它们。使用委托(delegate)的原因可能是能够从与正在迭代的集合相同的集合中删除，而不必将它们保存在另一个构造中。

在这里，我只是将要删除的订阅者添加到另一个列表，然后遍历从原始列表(未测试)中删除的订阅者:

    Public Sub AddMessage(ByVal message As String) Implements IMessage.AddMessage
        Dim msgCallback As IMessageCallback

        Dim removedSubscribers As New List(Of IMessageCallback)()

        For Each msgCallback In subscribers
            If (CType(msgCallback, ICommunicationObject).State = CommunicationState.Opened) Then
                msgCallback.OnMessageAdded(message, DateTime.Now)
            Else
                removedSubscribers.Add(msgCallback)
            End If
        Next

        For Each msgCallback In removedSubscribers
            subscribers.Remove(msgCallback)
        Next
    End Sub