.NET Base Class Library (BCL)

Understanding the BCL

The BCL is organized into namespaces, with the most fundamental types residing in the System namespace. It provides types for:

• Basic data types (integers, strings, booleans)
• Collections (lists, dictionaries, arrays)
• Input and output operations
• Networking
• Exception handling
• Reflection
• Threading
• And much more...

By leveraging the BCL, developers can significantly reduce the amount of boilerplate code they need to write, focusing instead on the unique logic of their applications.

Collections

The BCL offers robust support for managing groups of objects. The primary namespace for collections is System.Collections and System.Collections.Generic.

Common Collection Types:

• List<T>: A dynamically sized array.
• Dictionary<TKey, TValue>: A collection of key/value pairs.
• HashSet<T>: A collection that contains no duplicate elements.
• Queue<T>: A First-In, First-Out (FIFO) collection.
• Stack<T>: A Last-In, First-Out (LIFO) collection.

using System.Collections.Generic;

var numbers = new List { 1, 2, 3, 4, 5 };
numbers.Add(6);
Console.WriteLine(numbers[0]); // Output: 1
                    

Data Access

Accessing and manipulating data is a critical aspect of application development. The BCL provides namespaces like System.Data for working with databases.

Key Components:

• DataTable: Represents an in-memory collection of data that resembles a table.
• DataSet: A collection of DataTable objects.
• DbConnection, DbCommand, DbDataReader: Base classes for database-specific operations.

For modern data access patterns, consider using Entity Framework Core.

Input/Output (IO)

The System.IO namespace provides classes for reading from and writing to various data streams and files.

Common IO Operations:

• File: Provides static methods for creating, copying, deleting, moving, and opening files.
• Directory: Provides static methods for creating, moving, and enumerating directories and subdirectories.
• Stream: An abstract base class that represents a sequence of bytes.
• StreamReader, StreamWriter: For reading and writing text to streams.

using System.IO;

// Writing to a file
using (StreamWriter writer = new StreamWriter("example.txt"))
{
    writer.WriteLine("Hello, BCL!");
}

// Reading from a file
using (StreamReader reader = new StreamReader("example.txt"))
{
    string line = reader.ReadLine();
    Console.WriteLine(line); // Output: Hello, BCL!
}
                    

Networking

The System.Net namespace and its sub-namespaces provide classes for network communication, including HTTP, TCP, and UDP protocols.

Core Classes:

• HttpClient: Used for sending HTTP requests and receiving HTTP responses from a resource identified by a URI.
• IPAddress: Represents an Internet Protocol (IP) address.
• TcpListener, TcpClient: For TCP socket programming.

Reflection

Reflection allows you to inspect the metadata of assemblies, modules, and types at runtime. The System.Reflection namespace is key here.

Use Cases:

• Examining types and their members (methods, properties, fields).
• Dynamically creating instances of types.
• Invoking methods at runtime.

using System.Reflection;

Type stringType = typeof(string);
MethodInfo[] methods = stringType.GetMethods();

Console.WriteLine($"Methods of {stringType.Name}:");
foreach (var method in methods)
{
    Console.WriteLine($"- {method.Name}");
}
                    

Security

The BCL includes components for implementing security features, such as cryptography and identity management, primarily within the System.Security namespace.

Examples:

• Hashing algorithms (e.g., SHA256)
• Encryption/Decryption (e.g., AES)
• Access control

Threading

Concurrency and parallel processing are supported through the System.Threading namespace.

Key Types:

• Thread: Represents an operating system thread.
• ThreadPool: Manages a pool of threads for efficient execution of asynchronous operations.
• Synchronization primitives (e.g., lock, Mutex, Semaphore)

For more advanced asynchronous programming, explore System.Threading.Tasks (Task Parallel Library).

XML Processing

The BCL provides powerful tools for parsing, querying, and transforming XML documents, primarily in the System.Xml namespace.

Key Classes:

• XmlDocument: Represents an XML document as a tree structure.
• XmlReader, XmlWriter: For forward-only, high-performance XML reading and writing.
• LINQ to XML (System.Xml.Linq): A modern API for querying and manipulating XML in a more object-oriented way.

using System.Xml.Linq;

XDocument doc = XDocument.Parse("");
var title = doc.Root.Element("book").Element("title").Value;
Console.WriteLine(title); // Output: The Great Gatsby
                    

Date and Time

Working with dates and times is straightforward with the System namespace's DateTime and TimeSpan structures.

Core Types:

• DateTime: Represents an instant in time, typically expressed as a date and time of day.
• TimeSpan: Represents a time interval or duration.

DateTime now = DateTime.Now;
DateTime futureDate = now.AddDays(7);
TimeSpan duration = futureDate - now;

Console.WriteLine($"Now: {now}");
Console.WriteLine($"In 7 days: {futureDate}");
Console.WriteLine($"Duration: {duration.TotalDays} days");
                    

Serialization

Serialization is the process of converting an object into a stream of bytes that can be stored or transmitted. Deserialization is the reverse process.

Common Serializers:

• BinaryFormatter: Serializes objects into a binary format (System.Runtime.Serialization.Formatters.Binary).
• XmlSerializer: Serializes objects into XML format (System.Xml.Serialization).
• DataContractSerializer: Used for WCF services and other scenarios (System.Runtime.Serialization).
• System.Text.Json: A modern, high-performance JSON serializer (available in .NET Core and later).