Converting event-handling code from C# to VB.NET

Question

I am trying to convert this code written in C# to 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);

This is what I have currently, but it always throws an error when I run it:

' 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

Is there something that I am doing wrong?

Here is the rest of my code:

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

[This site](http://www.developerfusion.com/tools/convert/csharp-to-vb/) is a good tool for converting .net languages. — Jim, Dec 16 '11 at 14:40

score 3 · Answer 1 · answered Dec 15 '11 at 20:45

3

Try this:

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

I used http://converter.telerik.com/ which usually works well for me

answered Dec 15 '11 at 20:45

Leopold Stotch

1,452
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same here.. that's how I got the answer quickly.. LOL – MethodMan Dec 15 '11 at 20:46
No that didn't work. I also use that site and it is pretty good, I agree. But what I am getting with your code is that I cannot call the event directly. That is why I tried to add a handler instead. – adam bond Dec 15 '11 at 20:49
1

can you post the exact code that you are using.. perhaps we are not seeing some Encapsulated property's or Class Access levels – MethodMan Dec 15 '11 at 20:50

score 0 · Answer 2 · answered Dec 15 '11 at 20:45

try this and see if it will work

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

score -1 · Answer 3 · answered Dec 16 '11 at 05:27

First of all, the C# code isn't correct.

// 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);

it should be,

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

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

and the VB would be,

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

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

as and TryCast first check the type of the instance to see if it matches the cast type. If it doesn't, it'll return null, and you'll get a NullReferenceException. Instead, you should be casting the type directly, either using (Type)instance or CType(instance, Type). Not that's going to make a difference, logically, but you should still understand the difference. :)

Converting event-handling code from C# to VB.NET

3 Answers3