Question

我正在尝试将用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);

这是我目前所拥有的，但是当我运行它时总是会抛出错误：

' 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

有什么我做错了吗？

以下是我的其余代码：

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)

我使用的http://converter.telerik.com/通常适用于我

Answer 2

试试这个并查看它是否可行

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);

，VB就是，

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，它将返回null，并且您将获得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，这不会有所作为，但你仍然应该了解其中的差异。：）

将事件处理代码从C＃转换为VB.NET

3 个答案: