Understanding Delegates in .NET Core: A Comprehensive Guide
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Chapter 1: Introduction to Delegates
In .NET Core, delegates function as type-safe references to methods, enabling direct access to methods. They play a vital role in areas such as event handling, callbacks, and LINQ queries. To better understand delegates, let’s consider a practical example involving a library management system.
Imagine you are developing a library system that allows users to filter books based on specific criteria like genre or year of publication. You can implement this filtering capability using delegates.
First, you need to create a delegate type that represents a criterion for filtering:
// Define a delegate type for filtering books
public delegate bool BookFilterDelegate(Book book);
Next, define a Book class that represents each book in your library:
public class Book
{
public string Title { get; set; }
public string Author { get; set; }
public int PublicationYear { get; set; }
public string Genre { get; set; }
}
If you wish to filter books by their publication year, you can define a method that matches the BookFilterDelegate signature:
public static bool FilterByPublicationYear(Book book)
{
// Filter books published after 2010
return book.PublicationYear > 2010;
}
Similarly, if you want to filter books by genre, you can create another method:
public static bool FilterByGenre(Book book)
{
// Filter books in the "Fantasy" genre
return book.Genre == "Fantasy";
}
Now, let's see how these filters can be utilized:
class Program
{
static void Main(string[] args)
{
// Assuming you have a list of books
List<Book> books = GetBooks();
// Filter books using the delegate
List<Book> fantasyBooks = FilterBooks(books, FilterByGenre);
List<Book> recentBooks = FilterBooks(books, FilterByPublicationYear);
// Display filtered books
Console.WriteLine("Fantasy Books:");
foreach (var book in fantasyBooks)
{
Console.WriteLine($"{book.Title} by {book.Author}");}
Console.WriteLine("nRecent Books:");
foreach (var book in recentBooks)
{
Console.WriteLine($"{book.Title} ({book.PublicationYear}) by {book.Author}");}
}
// Filter books based on the provided criteria using a delegate
static List<Book> FilterBooks(List<Book> books, BookFilterDelegate filter)
{
List<Book> filteredBooks = new List<Book>();
foreach (var book in books)
{
if (filter(book))
{
filteredBooks.Add(book);}
}
return filteredBooks;
}
// Mock method to retrieve a list of books
static List<Book> GetBooks()
{
return new List<Book>
{
new Book { Title = "Harry Potter and the Philosopher's Stone", Author = "J.K. Rowling", PublicationYear = 1997, Genre = "Fantasy" },
new Book { Title = "The Name of the Wind", Author = "Patrick Rothfuss", PublicationYear = 2007, Genre = "Fantasy" },
new Book { Title = "Mistborn: The Final Empire", Author = "Brandon Sanderson", PublicationYear = 2006, Genre = "Fantasy" },
new Book { Title = "The Way of Kings", Author = "Brandon Sanderson", PublicationYear = 2010, Genre = "Fantasy" },
new Book { Title = "The Hunger Games", Author = "Suzanne Collins", PublicationYear = 2008, Genre = "Young Adult" },
new Book { Title = "Divergent", Author = "Veronica Roth", PublicationYear = 2011, Genre = "Young Adult" },
new Book { Title = "The Martian", Author = "Andy Weir", PublicationYear = 2011, Genre = "Science Fiction" }
};
}
}
In this scenario, the FilterBooks method takes a list of books and a delegate that specifies the filtering logic. It iterates through each book and applies the filtering criteria defined by the delegate. This approach allows for a flexible filtering mechanism without tightly coupling the logic with the FilterBooks method.
Using delegates enables you to easily switch between various filtering criteria without the need to alter the FilterBooks method itself, highlighting the versatility and power of delegates in .NET Core applications.
Chapter 2: Practical Implementation of Delegates
The first video provides a foundational overview of delegates and events in C#, specifically designed for new .NET developers.
The second video delivers a concise, 8-minute tutorial on C# delegates, aimed at helping you learn .NET quickly and effectively.