C event accessor detail

We can control the behavior of event operators += and -= by defining event accessors for events

The & # 8226; There are two accessors :add and remove
The & # 8226; An accessor that declares an event looks similar to declaring a property

The following example demonstrates a declaration with accessors. Both accessors have implicit value parameters called value, which take references to instances or static methods

public event EventHandler Elapsed
{
    add
    {
        //...  perform += The code for the operator 
    }

     remove
     {
        //...  perform -= The code for the operator 
     }
}

Once the event accessor is declared, the event does not contain any embedded delegate objects. We must implement our own mechanism to store and remove the method of the event

Event accessors are represented as void methods, which means that return statements that return values cannot be used

Complete example:

// The statement 1 a delegate
    delegate void EventHandler();
    class MyClass
    {
        // The statement 1 A member variable to hold an event handle that is called when the event is fired delegate ) 
        private EventHandler m_Handler = null;
        // Trigger events 
        public void FireAEvent()
        {
            if (m_Handler != null)
            {
                m_Handler();
            }
        }
        // The statement event 
        public event EventHandler AEvent
        {
            // Add accessor 
            add
            {
                // Pay attention to , The accessor actually contains 1 called value Implied parameter of 
                // The value of this parameter is the client call += " delegate
                Console.WriteLine("AEvent add Is called ,value the HashCode for :" + value.GetHashCode());
                if (value != null)
                {
                    // Set up the m_Handler Domain saves new handler
                    m_Handler = value;
                }
            }
            // Delete accessor 
            remove
            {
                Console.WriteLine("AEvent remove Is called ,value the HashCode for :" + value.GetHashCode());
                if (value == m_Handler)
                {
                    // Set up the m_Handler for null, The event will no longer be triggered 
                    m_Handler = null;
                }
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            MyClass obj = new MyClass();
            // Create a delegate 
            EventHandler MyHandler = new EventHandler(MyEventHandler);
            MyHandler += MyEventHandle2;
            // Register the delegate to the event 
            obj.AEvent += MyHandler;
            // Trigger events 
            obj.FireAEvent();
            // Revoke the delegate from the event 
            obj.AEvent -= MyHandler;
            // Refiring event 
            obj.FireAEvent();

            Console.ReadKey();
        }
        // Event handler 
        static void MyEventHandler()
        {
            Console.WriteLine("This is a Event!");
        }
        // Event handler 
        static void MyEventHandle2()
        {
            Console.WriteLine("This is a Event2!");
        }
    }