转换事件处理从C＃代码到VB.NET

Question

我试图把这段代码转换写在C＃到VB：

// Initialize the Message Broker Events 
(Application.Current as App).MessageBroker.MessageReceived += new MessageReceivedEventHandler(MessageBroker_MessageReceived); 
(Application.Current as App).MessageBroker.MessageReceived += new MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived); 

这是我现在，但它总是抛出当我运行一个错误它：

' Initialize the Message Broker Events 
AddHandler TryCast(Application.Current, App).MessageBroker.MessageReceived, AddressOf MessageBroker_MessageReceived 
AddHandler TryCast(Application.Current, App).MessageBroker.MessageReceived, AddressOf MessageBroker_SpecialMessageReceived 

有什么，我做错了吗？

这里是我的代码的其余部分：

Partial Public Class MainWindow 
Inherits Window 

Public Sub New() 
    InitializeComponent() 

    ' Initialize the Message Broker Events 
    'AddHandler TryCast(Application.Current, App).MessageBroker.MessageReceived, AddressOf MessageBroker_MessageReceived 
    'AddHandler TryCast(Application.Current, App).MessageBroker.MessageReceived, AddressOf MessageBroker_SpecialMessageReceived 

    TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_MessageReceived) 
    TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived) 

End Sub 

Private Sub MessageBroker_MessageReceived(ByVal sender As Object, ByVal e As MessageBrokerEventArgs) 
    ' Use this event to receive all messages 
    Select Case e.MessageName.ToLower() 
     Case "message1" 
      ' Do something with this message 
      Exit Select 
     Case "message2" 
      ' Do something with this message 
      Exit Select 
     Case "etc." 
      ' Do something with this message 
      Exit Select 
     Case Else 

      If Not String.IsNullOrEmpty(e.MessageObject.MessageBody) Then 
       MessageBox.Show(e.MessageObject.MessageBody) 
      End If 
      Exit Select 
    End Select 
End Sub 

Private Sub MessageBroker_SpecialMessageReceived(ByVal sender As Object, ByVal e As MessageBrokerEventArgs) 
    ' Use this event to receive any special message objects 
    If TypeOf e.MessageObject Is MySpecialMessage Then 
     MessageBox.Show(DirectCast(e.MessageObject, MySpecialMessage).SpecialMessage) 
    End If 
End Sub 

Answer 1

试试这个：

TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_MessageReceived) 
TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived) 

我用http://converter.telerik.com/通常很适合我

Answer 2

试试这个，看看它是否会工作

TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_MessageReceived) 
TryCast(Application.Current, App).MessageBroker.MessageReceived += New MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived) 

Answer 3

首先，C＃代码不正确。

// Initialize the Message Broker Events 
(Application.Current as App).MessageBroker.MessageReceived += 
    new MessageReceivedEventHandler(MessageBroker_MessageReceived); 

(Application.Current as App).MessageBroker.MessageReceived += 
    new MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived); 

它应该是，

// Initialize the Message Broker Events 
((App)Application.Current).MessageBroker.MessageReceived += 
    new MessageReceivedEventHandler(MessageBroker_MessageReceived); 

((App)Application.Current).MessageBroker.MessageReceived += 
    new MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived); 

和VB会，

CType(Application.Current, App).MessageBroker.MessageReceived += 
    New MessageReceivedEventHandler(MessageBroker_MessageReceived) 

CType(Application.Current, App).MessageBroker.MessageReceived += 
    New MessageReceivedEventHandler(MessageBroker_SpecialMessageReceived) 

as和TryCast首先检查实例的类型，看它是否投类型相匹配。如果没有，它会返回null，并且您将得到一个NullReferenceException。相反，您应该直接使用(Type)instance或CType(instance, Type)来投射类型。从逻辑上说，这不会有什么不同，但你仍应该了解其中的差异。 :)