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
![Event]()
Happy Coding.