Understanding Delegates in C#
Delegates are a fundamental feature of C# that allow you to pass methods as arguments to other methods. They are type-safe function pointers, enabling dynamic method calls. Delegates are widely used in event handling and callback mechanisms.
Defining and Using Delegates
A delegate is defined using the delegate keyword. Here is a basic syntax:
delegate returnType DelegateName(parameters);
Example 1: Basic Delegate
Let's create a delegate that takes two integers and returns their sum.
using System;
class Program
{
// Define a delegate
public delegate int Operation(int x, int y);
static void Main(string[] args)
{
// Method that matches the delegate signature
int Add(int a, int b) => a + b;
// Create an instance of the delegate
Operation operation = Add;
// Call the delegate
int result = operation(10, 20);
Console.WriteLine($"Sum: {result}");
}
}
Multicast Delegates
Delegates can hold references to multiple methods. When the delegate is invoked, all methods in its invocation list are executed.
using System;
class Program
{
public delegate void Notify();
static void Method1() => Console.WriteLine("Method1 called");
static void Method2() => Console.WriteLine("Method2 called");
static void Main(string[] args)
{
Notify notify = Method1;
notify += Method2;
// Invoke delegate
notify();
}
}
Example 2: Delegates with Lambda Expressions
Delegates can be used with anonymous methods or lambda expressions for conciseness.
using System;
class Program
{
public delegate void Greet(string name);
static void Main(string[] args)
{
// Using a lambda expression
Greet greet = name => Console.WriteLine($"Hello, {name}!");
greet("John");
}
}
Example 3: Delegate for Sorting
Delegates can be used to pass sorting logic to methods. For example:
using System;
class Program
{
public delegate int Comparison(int x, int y);
static int AscendingOrder(int a, int b) => a - b;
static int DescendingOrder(int a, int b) => b - a;
static void Sort(int[] array, Comparison comparison)
{
for (int i = 0; i < array.Length - 1; i++)
{
for (int j = i + 1; j < array.Length; j++)
{
if (comparison(array[i], array[j]) > 0)
{
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
}
}
}
static void Main(string[] args)
{
int[] numbers = { 5, 3, 8, 1, 2 };
Console.WriteLine("Original array: " + string.Join(", ", numbers));
Sort(numbers, AscendingOrder);
Console.WriteLine("Sorted in ascending order: " + string.Join(", ", numbers));
Sort(numbers, DescendingOrder);
Console.WriteLine("Sorted in descending order: " + string.Join(", ", numbers));
}
}
Example 4: Delegate with Predicate
Using a delegate to filter elements in a collection:
using System;
using System.Collections.Generic;
class Program
{
public delegate bool Filter(int number);
static List FilterNumbers(List numbers, Filter filter)
{
List result = new List();
foreach (var number in numbers)
{
if (filter(number))
{
result.Add(number);
}
}
return result;
}
static void Main(string[] args)
{
List numbers = new List { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// Filtering even numbers
List evenNumbers = FilterNumbers(numbers, n => n % 2 == 0);
Console.WriteLine("Even numbers: " + string.Join(", ", evenNumbers));
// Filtering odd numbers
List oddNumbers = FilterNumbers(numbers, n => n % 2 != 0);
Console.WriteLine("Odd numbers: " + string.Join(", ", oddNumbers));
}
}
Real-World Use Case: Event Handling
Delegates are commonly used in event handling. For instance:
using System;
class Program
{
public delegate void Notify(string message);
public static void OnNotification(string message)
{
Console.WriteLine($"Notification received: {message}");
}
static void Main(string[] args)
{
Notify notifier = OnNotification;
notifier("You have a new message.");
}
}
Advantages of Delegates
- Allows dynamic method invocation.
- Enables callback functionality.
- Supports event-driven programming.
In summary, delegates in C# provide a powerful way to work with methods dynamically. They form the backbone of events and callbacks, making them indispensable in modern C# programming.
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