Events

In my last post I tried to show some example on Delegate. Here I will give another example of Events.

In windows form based application or in web based application we use events very commonly(button click, page load etc). It is something like a function or method is registered to that event and whenever the event is fired the registered method executed.

In .net Events and Delegates works hand-in-hand to provide a program's functionality. For any pre-defined dot net events or user defined custom events can be registered with any kind of method but this process is done by a delegate, which specifies the signature of the method that is registered for the event. Below is the code as an example of simple Events declaration.

 

namespace Event
{    
    //public delegate void MyDelegate();
    public class EventProgram:Form
    {
        //public static event MyDelegate MyEvent;

        public EventProgram()
        {
            Button clickMe = new Button();

            clickMe.Parent = this;
            clickMe.Text = "Click Here";
            clickMe.Location = new Point(
                (ClientSize.Width - clickMe.Width) / 2,
                (ClientSize.Height - clickMe.Height) / 2);

            
            clickMe.Click += new EventHandler(OnClickMeClicked);

           // MyEvent += new MyDelegate(OnStartEvent);
                        
           // MyEvent();
        }

       
        public void OnClickMeClicked(object sender, EventArgs ea)
        {
            MessageBox.Show("My Button is Clicked.");
        }

        
        public void OnStartEvent()
        {
            MessageBox.Show("My Start Event Started :) ");
        }
       
        static void Main()
        {         
            
            Application.Run(new EventProgram());
           
        }
    }
}

In the above example we are using a windows form containing a button only. Clicking on that button the registered method will be executed.

clickMe.Click += new EventHandler(OnClickMeClicked);

By this line we have assigned a delegate for the click event of the button. and the implementation of the delegate is as below :

public void OnClickMeClicked(object sender, EventArgs ea)

{

MessageBox.Show("My Button is Clicked.");

}

Look carefully that we didnot send the argument 'sender' and 'ea' but we put the method name.

Also in the same code I have added a custom event sample which is commented. Just unblock the lines of code and it will clear the understating how delegate is being used for method registering in events.