Question

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

Answer 1

There is an interesting discussion in question 1129517 around how to do this very thing in C#.

Since the class that contains the Event was written in C#, the delegate semantics do apply, and those techniques should work for you. However, you’ll need to translate the source to VB.NET for your unit test.

Given the following class in a C# assembly:

public class Triggerific
{
    public event EventHandler Trigger;

    private static void OnTriggerTriggered(object sender, EventArgs e)
    {
        Console.WriteLine("Triggered!");
    }

    public void AddTrigger()
    {
        Trigger += OnTriggerTriggered;
    }
}

Here is some VB.NET code which will correctly determine if a handler was registered for the Trigger event:

<TestMethod()> _
Public Sub TriggerTest()
    Dim cut As New Triggerific
    cut.AddTrigger()

    Assert.IsNotNull(GetEventHandler(cut, "Trigger"))
End Sub

Private Shared Function GetEventHandler(ByVal classInstance As Object, ByVal eventName As String) As EventHandler
    Dim classType As Type = classInstance.[GetType]()
    Dim eventField As FieldInfo = classType.GetField(eventName, BindingFlags.GetField Or BindingFlags.NonPublic Or BindingFlags.Instance)

    Dim eventDelegate As EventHandler = DirectCast(eventField.GetValue(classInstance), EventHandler)

    ' eventDelegate will be null/Nothing if no listeners are attached to the event
    Return eventDelegate
End Function