How to expose an event in a c# class?

I am building a simple class to开发者_开发知识库 hold related methods. Part of this code includes synchronising to a database. The built in SyncOrchestrator class includes a SessionProgress event handler which I can wire up an event to.

What I would like to do is instance my class and then hook up an some code to this event so that I can display a progress bar (ill be using BGWorker).

So, my question is probably c# 101, but how do I expose this event through my class the correct way so that I can wire it up?

Thanks

I think you're looking for something like this:

(I also suggest you read the Events tutorial on MSDN.)

public class SyncOrchestrator
{
    // ...

    public event EventHandler<MyEventArgs> SessionProgress;

    protected virtual void OnSessionProgress(MyEventArgs e)
    {
        // Note the use of a temporary variable here to make the event raisin
        // thread-safe; may or may not be necessary in your case.
        var evt = this.SessionProgress;
        if (evt  != null)
            evt (this, e);
    }

    // ...
}

where the MyEventArgs type is derived from the EventArgs base type and contains your progress information.

You raise the event from within the class by calling OnSessionProgress(...).

Register your event handler in any consumer class by doing:

// myMethodDelegate can just be the name of a method of appropiate signature,
// since C# 2.0 does auto-conversion to the delegate.
foo.SessionProgress += myMethodDelegate;

Similarly, use -= to unregister the event; often not explicitly required.

Like this:

public event EventHandlerDelegate EventName;

EventHandlerDelegate should obviously be the name of a delegate type that you expect people to provide to the event handler like so:

anObject.EventName += new EventHandlerDelegate(SomeMethod);

When calling the event, make sure you use this pattern:

var h = EventName;
if (h != null)
    h(...);

Otherwise you risk the event handler becoming null in between your test and actually calling the event.

Also, see the official documentation on MSDN.