Events

This is a discussion on Events within the C# Programming forums, part of the General Programming Boards category; I am a little confuzed with events. To use them first you define a delegate signature. Like: Code: public delegate ...

  1. #1
    System Novice siavoshkc's Avatar
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    Events

    I am a little confuzed with events.
    To use them first you define a delegate signature. Like:
    Code:
    public delegate void ButtonEventHandler();
    Then we make a delegate (event) in our class. Like:
    Code:
    class TestButton 
    {
        public event ButtonEventHandler OnClick;
    
        // A method that triggers the event:
     public void Click()
        {
            OnClick();
        }
    }

    The class has a method or methods that trigger the event. The event is just a delegate that Click() invokes.

    For handling events we subscribe handlers to events. That is exactly adding more methods to a delegate (Except when accessors are used). Like:
    Code:
     TestButton mb = new TestButton();
            
     // Specify the method that will be triggered by the OnClick event.
     mb.OnClick += new ButtonEventHandler(TestHandler);
    
     // Specify an additional anonymous method.
     mb.OnClick += delegate { System.Console.WriteLine("Hello, World!"); };
    And event will be triggered by calling Click() method. Like:
    Code:
     // Trigger the event
     mb.Click();
    Everything is going fine. By raising the event, Click() method invokes OnClick event and because it is like a delegate it calls subscribed methods that are actually event handlers.
    Now my question is: What is the difference between a delegate and an event? A delegate has the same functionality of an event. What will happen if we don't write event keyword in the class?
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  2. #2
    System Novice siavoshkc's Avatar
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    I have also another question: Why MSDN writes this:
    Code:
    m_list.Changed += new ChangedEventHandler(ListChanged);
    When it can be written as this:
    Code:
    m_list.Changed += ListChanged;
    ???
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