How to subscribe to other class' events in c#?

Question

A simple scenario: a custom class that raises an event. I wish to consume this event inside a form and react to it. How do I do that? Code examples, please!

Note that the form and custom class are separate classes.

Answer 1

Inside your form:

void SubscribeToEvent(OtherClass theInstance)
{
    theInstance.SomeEvent += this.MyEventHandler;
}

void MyEventHandler(object sender, EventArgs args)
{
    // Do something on the event
}

You just subscribe to the event on the other class the same way you would to an event in your form. The three important things to remember:

1) You need to make sure your method (event handler) has the appropriate declaration to match up with the delegate type of the event on the other class.

2) The event on the other class needs to be visible to you (ie: public or internal).

3) Subscribe on a valid instance of the class, not the class itself.

Answer 2

Assuming your event is handled by EventHandler, this code works:

protected void Page_Load(object sender, EventArgs e)
{
    MyClass myObj = new MyClass();
    myObj.MyEvent += new EventHandler(this.HandleCustomEvent);
}

private void HandleCustomEvent(object sender, EventArgs e)
{
    //handle the event
}

If your "custom event" requires some other signature to handle, you'll need to use that one instead.

Answer 3

        public class EventThrower
        {
            public delegate void EventHandler(object sender, EventArgs args) ;
            public event EventHandler ThrowEvent = delegate{};

            public void SomethingHappened()
            {
                ThrowEvent(this, new EventArgs());
            }
        }

        public class EventSubscriber
        {
            private EventThrower _Thrower;

            public EventSubscriber()
            {
                _Thrower = new EventThrower();
                //using lambda expression..could use method like other answers on here
                _Thrower.ThrowEvent += (sender, args) => { DoSomething(); };
            }

            private void DoSomething()
            {
               //Handle event.....
            }
        }