Custom Events in C#

In this article, I shall demonstrate how to create custom events in C#. Before going through this article I recommend you get some knowledge of Delegates.

Example

In this example, I have created a custom event handler for displaying Employee data. This event is raised when a new Employee is added to a List.

Step 1: Create a custom class named EmployeeArgs.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CustomEvents
{
    public delegate void EmployeeAddDelegate(EmployeeArgs e);
    public class EmployeeArgs : EventArgs
    {
       public Employee _employee;
       public EmployeeArgs(Employee employee)
       {
           this._employee = employee;
       }
    }
}

EmployeeArgs is inherited from the predefined class EventArgs in the .Net Framework.

A delegate is declared with EmployeeArgs as the parameter as in the following:

public delegate void EmployeeAddDelegate(EmployeeArgs e);

Step 2: Create a Listener class for our custom event. Our handler will call the function ShowEmployees as in the following:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CustomEvents
{
    public class EmployeeListener
    {
       public void ShowEmployees(EmployeeArgs e)
       {
           // Call the model class to display the results on screen.
           Employee.ShowEmployees(e);
       }
    }
}

Step 3: Create an Employee Class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CustomEvents
{
    public class Employee
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public static void ShowEmployees(EmployeeArgs e)
        {
            Console.WriteLine("New Employee Added...");
            Console.WriteLine("Employee ID = {0}, Employee Name = {1} ", e._employee.ID, e._employee.Name);
        }
    }
}

Step 4: Construct the main class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace CustomEvents
{
    class Program
    {
        public static event EmployeeAddDelegate _employeeEventHandler;
        public static List<Employee> lstEmployees = null;
        public static EmployeeListener employeeListener = null;
        public static Employee emp1, emp2;
        static void Main(string[] args)
        {
            lstEmployees = new List<Employee>();
            employeeListener = new EmployeeListener();
            // Assigning the function ShowEmployees to the event handler.
            _employeeEventHandler += new EmployeeAddDelegate(employeeListener.ShowEmployees);
            //Initialising Employees
            emp1 = new Employee { ID = 10456, Name = "Madhav" };
            emp2= new Employee { ID = 15621, Name = "Praveen" };
            //Add the employees
            AddEmployees(emp1);
            AddEmployees(emp2);
            Console.ReadLine();
        }
        private static void AddEmployees(Employee employee)
        {
            if (employee != null)
            {
                EmployeeArgs e = new EmployeeArgs(employee);
                lstEmployees.Add(employee);
                //Event handling call
                OnEmployeeAdd(e);
            }
        }
        private static void OnEmployeeAdd(EmployeeArgs e)
        {
            //Event Handler is raised. Here ShowEmployees function in EmployeeListener is     raised.
            // Eventhandler calls the ShowEmployees function in EmployeeListener class.
            if (_employeeEventHandler != null)
            {
                _employeeEventHandler(e);
            }
        }
    }
}

I have provided comments in the main class in such a way that it helps you understand the logic and its implementation.

Please find the attached source code for a better understanding.

Output

Happy Coding.