c# - 将 C# WCF 应用程序转换为 Visual Basic

Question

我正在尝试用 Visual Basic 编写一个简单/小型的 Windows Communication Foundation 服务应用程序(但我在 VB 方面非常新手)，并且我在网上找到的所有好示例都是用 C# 编写的。到目前为止，我已经让我的 WCF 服务应用程序正常工作，但现在我正在尝试添加回调功能，并且程序变得更加复杂。在 C# 示例代码中，我了解一切是如何工作的，但我在将使用委托(delegate)的代码部分转换为 VB 时遇到问题。有人可以展示 VB 等效项吗？

这是我用作引用的 C# 代码示例:

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>();

        //The code in this AddMessage method is what I'd like to see re-written in VB...
        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;
            }
        }
    }        
}

我想我可以做这样的事情，但我不知道如何将消息字符串从 AddMessage 传递到 DoSomething...

Dim subscribers As New List(Of IMessageCallback)

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

    Dim action As Action(Of IMessageCallback)
    action = AddressOf DoSomething
subscribers.ForEach(action)

'Or this instead of the above three lines:
'subscribers.ForEach(AddressOf DoSomething)

End Sub

Public Sub DoSomething(ByVal callback As IMessageCallback)

    'I am also confused by:
    '((ICommunicationObject)callback).State
    'Is that casting the callback object as type ICommunicationObject? 
    'How is that done in VB?

End Sub

Answer 1

所以你不知道 secret converter ？

Public Class MessageService
    Implements IMessage
    Private Shared ReadOnly subscribers As New List(Of IMessageCallback)()

    'The code in this AddMessage method is what I'd like to see re-written in VB...
    Public Sub AddMessage(message As String)

        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
        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
        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