RE: Delegates/events

Hi Peter ,

In "AMethod", the parameter "callback" is of type
"EventHandler<EventArgs>", which is a delegate instead of event. So you can
not pass an event to this method. You should explicitly construct a
"EventHandler<EventArgs>" delegate(which must explictly wrap a method) and
pass this delegate to the method, like this:

public class First
{
public event EventHandler<EventArgs> MyEvent;
public void OnMyEvent(object sender, EventArgs args)
{
if (this.MyEvent != null)
this.MyEvent(sender, args);
}
}
public class Second
{
public void Method(First aInstance)
{
Third th = new Third();
EventHandler<EventArgs> EH = new
EventHandler<EventArgs>(aInstance.OnMyEvent);
th.AMethod(EH);
}
}

public class Third
{
public void AMethod(EventHandler<EventArgs> callback)
{
if (callback != null)
callback(this, new EventArgs());
}
}

Additionally, the code snippet provided by "PS" is almost the same as this,
but it uses an implicit way of constructing "EventHandler<EventArgs>". That
is when passing "aInstance.OnMyEvent" to the method, the C# compiler will
emit an explicit construct to "EventHandler<EventArgs>" delegate like below:
public void Method(Form1.First aInstance)
{
Form1.Third th = new Form1.Third();
th.AMethod(new EventHandler<EventArgs>(aInstance.OnMyEvent));
}

Hope this helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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.

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