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

Question

In C# I can test for this...

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


        

Answer 1

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