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Is there a way to know in VB.NET if a handler has been registered for an event?

Asked 2010-06-01T19:15:07.620
12

In C# I can test for this...

public event EventHandler Trigger;
protected void OnTrigger(EventArgs e)
{
    if (Trigger != null)
        Trigger(this, e);
}

Is there a way to do this in VB.NET? Test for null I mean?

MORE INFO

I forgot to mention. I have classes written in C# but I am writing my unit tests in VB.NET.

I am trying this in the unit test...

If myObject.Trigger IsNot Nothing Then  
    ''#do something
End If

This is causing a compile time error which says ... "Public Event Trigger is an Event and cannot be called directly. Use the RaiseEvent statement to raise an event."

Seth

c# .net vb.net events null
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1 Answer

9

First of all, there's a problem with your c# code. It should read like this to reduce the likelihood of a race condition on removing the last handler in a separate thread at just the wrong time (hint on why it works: mulit-cast delegates are immutable):

public event EventHandler Trigger;
protected void OnTrigger(EventArgs e)
{
    var temp = Trigger;
    if (temp != null)
        temp(this, e);
}

Secondly, there's no need for this code at all in VB.Net. VB handles events a little differently, such that you should not check at all whether any handlers are registered. It's safe and preferred to just raise the event:

Public Event Trigger As EventHandler
Friend Sub OnTrigger(ByVal e As EventArgs)
    RaiseEvent Trigger(Me, e)
End Sub
answered 2010-06-01T19:21:15.500

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