explanation of an event and eventhandler c# code example

Example: c# events

// --------------------- HOW TO CREATE EVENTS? ----------------------- //
// 1º - Main (Start the program)
// 2º - Publisher (the one that sends the event) 
// 3º - Subscriber (the one that receives the event)


// PUBLISHER:
class Publisher
{
   // 1º Create a delegate
   public delegate void MyEventHandler (object source, EventArgs args);

   // 2º Create an event based on that delegate
   public event MyEventHandler myEvents;

   // 3º Raise the event. For example, create a method that does:
   protected virtual void Method1()
   {
      if(myEvents != null)
      {
           myEvents(this, EventArgs.Empty);  // Calling the event if it points to some other method 
      }
   }

   public void Method2()
   {
      Console.WriteLine("This method is called from the Main function...");

      // Continuation of 3º step
      Method1();
     
    }
}


// SUBSCRIBER:
public class Subscriber
{
     public void Method1(object source, EventArgs e)
     {
            Console.WriteLine("The work done by the subscriber after the event was raised...");
      }
}


// MAIN:
class Program
{
   static void Main(string[] args)
   {
      var myPublisher = new Publisher();
      var mySubscriber = new Subscriber();

      // Give the Event a pointer to the function inside the class Subscriber
      myPublisher.myEvents += mySubscriber.Method1;

      myPublisher.Method2();
   }
}


// ----------- HOW TO PASS ARGUMENTS/DATA THROUGH EVENTS? ------------ //
// You have to create an EventArgs class, like:

public class MyNewEventArgs : EventArgs    // It will inherit from the EventArgs class, and you can add on top of that, some new information 
{
	public string newData {get; set;}	

}


// Then, you just need to change the following (in the code above):
// |  1º |
public delegate void EventHandler (object source, MyNewEventArgs args);  // Substitute EventArgs for MyNewEventArgs
// |  2º |
myEvents(this, new MyNewEventArgs() { newData = "Hello World!"} );  // Create an instance of the MyNewEventArgs class and pass it as a parameter of myEvents   
// |  3º |
public void Method1(object source, MyNewEventArgs e)   // Update all the other methods (substitute EventArgs for MyNewEventArgs)

// Now you can use the data inside the "e" variable on the Subscribers methods