将事件处理代码从c#转换为VB.NET

Question

我正在尝试将这段用c#编写的代码转换为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);

这是我目前拥有的，但是当我运行它时它总是抛出一个错误:

' 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

我做错了什么吗?

下面是我剩下的代码:

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)

我使用http://converter.telerik.com/，这通常对我来说很好

Answer 2

试试这个，看看是否会起作用

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);

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);

而VB是

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，看它是否与强制转换类型匹配。如果没有，它会返回null，你会得到一个NullReferenceException。相反，您应该使用(Type)instance或CType(instance, Type)直接转换类型。从逻辑上讲，这不会有什么区别，但你仍然应该理解其中的区别。:)