The technology framework varies according on the context in which the program will run, as is common with Microsoft technology, which comes with numerous environments like Desktop, Web, Mobile apps, etc. Thus, the application needs to be planned and built based on the environment. But difficulties will now arise.

Step 1: Please verify that the current application target framework is in place before moving to the higher version. After selecting Solution Properties, check as shown below.

Step 2: To access the upgrade button menu, simply perform a right-click on the solution.

Step 3: The window for the upgrade assistant will appear and ask what has to be done next to upgrade the project.

Step 4: You'll be prompted to choose the target framework in this window.

Step 5: At this point, you may choose which components to upgrade to the newest target framework or migrate to an updated version of.

Step 6: As I pick every component, the system will verify and either provide you with the most recent code alteration or advise you to make the necessary adjustments. Improvement is underway. It will require some time to finish and provide the report.

Step 7: The report is now generated and displayed in the window for the upgrading assistant. Please take the example below into consideration. The project output will vary if the project is an enterprise application.

Step 8: The Visual Studio output window allows the developer to view the current status.

After the DotNet or.Net upgrade assistant is finished, we must follow its recommendations and make changes to the code base. Step 7 indicates that the.net8-windows target framework does not support MVVMLight. Thus, we must decide and update such packages. In this case, CommunityToolkit is an alternative to MVVMLight.Since MVVM is available in Nuget, the codebase must also be modified.

The Null Object Pattern is a behavioral design pattern that provides an object to stand in for the missing object in an interface. It's a way to offer an alternate action in situations when a null object would raise a null reference exception. In this post, we'll go deeply into the C# Null Object Pattern and gradually advance to more complicated scenarios.

The Pattern of Null Object Design What's that?
The use of the Null object pattern is one design strategy that facilitates the use of potentially undefined dependencies. This is done by using instances of a concrete class that implements a recognized interface in place of null references. Together with concrete classes that extend it and a null object class that provides a do-nothing version of the class that can be used anyplace we need to verify the null value, an abstract class detailing the various actions to be performed is constructed.

The Null Object Design Pattern's constituent parts
Customer
The client is the code that depends on an object that either implements a Dependency interface or extends an abstract DependencyBase class. The client uses this item to complete a task. The client shouldn't need to know which kind of object it is working with in order to handle both real and null objects in the same manner.

DependencyBase or Abstract Dependency
An abstract class or interface called DependencyBase specifies the methods that must be implemented by all concrete dependents, including the null object. The contract that all dependencies have to abide by is defined by this class.

Dependency or Real Dependency
The Client may utilize this class as a functional dependency. It is not necessary for the client to know if Dependency objects are actual or null in order to interact with them.

NullObject or Null Dependency
This is the class of null objects that the client may utilize as a dependency. While it implements every member specified by the DependencyBase abstract class, it lacks functionality. A null or non-existent dependency in the system is represented by a NullObject. Methods on a NullObject can be securely called by the client without resulting in errors or requiring null checks.

As an illustration,
Abstract Dependency
Here is the code for the ICar.cs file.
public interface ICar
{
    void Drive();

    void Stop();
}

Real Dependency
Here is the code for the SedanCar.cs file.
public class SedanCar : ICar
{
    public void Drive()
    {
        Console.WriteLine("Drive the sedan car.");
    }

    public void Stop()
    {
        Console.WriteLine("Stop the sedan car.");
    }
}

Null Object Dependency
Here is the code for the NullCar.cs file.
public class NullCar : ICar
{
    public void Drive()
    {

    }

    public void Stop()
    {

    }
}

Client
Here is the code for the CarService.cs file.
public class CarService(ICar car)
{
    private readonly ICar _car = car;

    public void Run()
    {
        Console.WriteLine($"Start run method. {nameof(ICar)}: {_car}");
        _car.Drive();
        _car.Stop();

        Console.WriteLine($"Complete run method. {nameof(ICar)}: {_car}");
        Console.WriteLine();
    }
}

Program
Here is the code for the Program.cs file.
var sedanCar = new SedanCar();
var carService = new CarService(sedanCar);

carService.Run();

var nullCar = new NullCar();
carService = new CarService(nullCar);

carService.Run();

Output

When to apply the Design Pattern for Null Objects?
When you want to provide a default or no-op implementation of an object's functionality to avoid null checks and handle null references gracefully, you can use the Null Object Design Pattern. The following situations call for the application of the Null Object Design Pattern.

• Default Behavior: This is the behavior you want to give an object in the event that its real implementation is unavailable or inappropriate.
• Avoid Null Checks: When you want to provide a null object implementation that may be used safely in place of a null reference, you can avoid having to do explicit null checks in your code.
• Consistent Interface: In situations when you need to give customers access to an interface that stays the same whether they are working with real or null objects.
• Simplifying Client Code: When you wish to spare client code from handling null references by letting them handle null objects in the same manner as actual objects.

When the Null Object Design Pattern should not be used?
The Null Object Design Pattern might not be appropriate in the following situations.

• Sophisticated Behavior: The Null Object Design Pattern is meant to provide simple default behavior; therefore, it might not be acceptable when the null object needs to implement sophisticated behavior or store state.
• Performance Considerations: It could be preferable to handle null references directly in the code if generating and utilizing null objects significantly increases overhead or complexity in the system.
• Confusion with Real Objects: Explicit null checks may be preferable in order to improve the readability and clarity of the code if there is a chance that null objects and real objects could be confused in the system.

Summary
A solid method for handling the lack of objects is provided by the Null Object Pattern, a design pattern. It lowers the possibility of runtime mistakes and simplifies client code by offering a default behavior and doing away with the necessity for null checks. To improve stability and maintainability, the Null Object Pattern can be a useful tool when building a new system or restructuring an old one.

We learned the new technique and evolved together.

Applications developed today do not make use of the System Thread class.Threading straight. It means you are still keeping legacy code if you see it in one of your projects. Is learning Thread API worthwhile? Well, that's a different subject altogether. The Thread API was introduced in.NET 1.0, as we well know, but it was not very user-friendly. Why then is it preferable not to utilize it?

• The underlying API that gives you direct control over everything is called Thread API. Although this choice seems appealing, you can become frustrated if you have more influence over something you don't understand.
• Gaining mastery over Thread API was not an easy feat. It has a rich history that you must really understand by delving into the OS's intricacies. It does seem a little frightening, but the Thread API makes you think in terms of Threads rather than jobs. Instead of focusing about building threads, developers should consider writing concurrent programming. Thread is an implementation detail and a physical concept.
• The process of creating a thread is costly.
• From the standpoint of understandability and maintainability, using Thread API introduces more complexity.

Microsoft introduced the ThreadPool class in.NET 2.0, which is an improvement over the Thread API. Isolating us from the Thread notion was the main advancement toward Threading. It is not necessary for you to consider threads. As a developer, you ought to consider tasks that need to be parallelized.

A wrapper around your threads is called ThreadPool.

Why is it a superior choice?

• You are no longer "the owner" of Threads thanks to ThreadPool. There is no need for manual development, intricate procedures, thread management issues, deadlock, etc. What do you think? You were the main issue, not a thread:)
• When and why to create threads are managed by ThreadPool. Put simply, let's say we have five approaches. You should use multithreading to run them. To run them, you require five methods, but ThreadPool might need to use two or three threads to finish your job. If you use a traditional thread API, the limit is determined by the thread count you utilize.

Every operation is a Thread, and it is not an optimized way of using it.

ThreadPool isolates us from The Thread stuff and provides a simple API to enter multithreading mode. Let’s modify our code and try to understand the value of using ThreadPool instead of Thread directly.
internal class Program
{
    static void Main(string[] args)
    {
        ThreadPool.QueueUserWorkItem((x) => ComplexTask());
        Thread.Sleep(1000);
        ThreadPool.QueueUserWorkItem((x) => ComplexTask());
        Thread.Sleep(1000);
        ThreadPool.QueueUserWorkItem((x) => ComplexTask());
        Thread.Sleep(1000);
        ThreadPool.QueueUserWorkItem((x) => ComplexTask());
        Thread.Sleep(1000);

        Console.ReadLine();
    }
    static void ComplexTask()
    {
        Console.WriteLine($"Running complex task in Thread={Environment.CurrentManagedThreadId}");
        //Thread.Sleep(40);
        Console.WriteLine($"Finishing complex task in Thread={Environment.CurrentManagedThreadId}");
    }
}

As you have probably noticed, ThreadPool optimizes the use of Thread. ThreadPool will utilize an existing thread rather than start a new one if any of them are free. Hold on a minute... Can we perform the same procedure together? Can we really execute the same Thread twice? Let's give it a shot.

You can’t run the same Thread twice but somehow ThreadPool can. ThreadPool can reuse Threads and it helps not to create a Thread every time when you have a block of code to run in multithreading mode. In classical .NET, depending on its version and your CPU architecture the capacity of Worker threads is different.

I have an x64 Intel processor running the most recent version of.NET (.NET 8) with 32767 worker threads with 1000 completion post threads. Typically, ThreadPool begins with just one thread in it. It may automatically increase Threads based on the circumstances. ThreadPool allows you to check the available threads.

In my case, I’m using the latest .NET ( .NET 8) with an x64 intel processor, and I have 32767 worker Threads with 1000 completion post Threads.

ThreadPool usually starts with 1 Thread in the pool. Depending on the context, it may automatically increase Threads. You can Check available threads in ThreadPool.
internal class Program
{
    static void Main(string[] args)
    {
        ThreadCalculator();
        for (int i = 0; i < 10; i++)
        {
            ThreadPool.QueueUserWorkItem((x) => ComplexTask());
        }
        Thread.Sleep(15);
        ThreadCalculator();
        Console.ReadLine();
    }
    static void ThreadCalculator()
    {
        ThreadPool.GetAvailableThreads(out int workerThreads, out int completionPortThreads);
        Console.WriteLine($"worker threads = {workerThreads}, " +
            $"and completion Port Threads = {completionPortThreads}");
    }
    static void ComplexTask()
    {
        Console.WriteLine($"Running complex task in Thread={Environment.CurrentManagedThreadId}");
        //Thread.Sleep(40);
        Console.WriteLine($"Finishing complex task in Thread={Environment.CurrentManagedThreadId}");
    }
}

The most used API in ThreadPool is, of course, QueueUserWorkItem. It has a generic version, also.
Well, we have another great concept called completion post Threads that we need to cover.

ThreadPool.QueueUserWorkItem is a method in C# that allows you to schedule tasks for execution in a thread pool. Here's a breakdown of its functionality:

Purpose
Schedule tasks to run asynchronously without creating and managing individual threads.
Leverages a pool of pre-created threads, improving performance and resource management.

How it works
You provide a delegate (like Action or WaitCallback) that represents the work you want to be done.
Optionally, you can pass an object containing data to be used by the delegate.

ThreadPool.QueueUserWorkItem adds the delegate and data (if provided) to the thread pool's queue.

When a thread from the pool becomes available, it picks up the first item from the queue and executes the delegate with the provided data.

Benefits or Why to Use It
Performance Boost: Reusing threads avoids the overhead of creating and destroying them for each task.
Resource Optimization: Maintains a controlled number of threads, preventing system overload.
Simplified Concurrency Management: The thread pool handles scheduling and ensures tasks are executed efficiently.

Additional notes
The thread pool can dynamically adjust the number of threads based on workload.
Tasks are queued if all threads are busy, ensuring none are dropped.

ThreadPool.QueueUserWorkItem has overloads, including a generic version for type safety and an option to influence thread selection.

Ok, but what about completion port Threads?
The concept of completionPortThreads within the ThreadPool class in C# might not be directly exposed as you might expect.
The ThreadPool class internally manages two types of threads.

• Worker Threads: These handle general-purpose tasks submitted through QueueUserWorkItem.
• I/O Completion Port Threads (Completion Port Threads): These are specialized threads optimized for processing asynchronous I/O operations.

Purpose of completion port threads
Asynchronous I/O operations typically involve waiting for network requests, file access, or other external events. Completion port threads efficiently wait for these events using a system mechanism called I/O Completion Ports (IOCP).

When an I/O operation completes, the corresponding completion port thread is notified, and it can then dequeue and process the completed task.

What is the value?

• Improved performance for asynchronous I/O bound tasks.
• Completion port threads avoid busy waiting, reducing CPU usage while waiting for I/O events.
• Dedicated threads for I/O operations prevent worker threads from being blocked, improving overall responsiveness.

Important Notes
You don't directly control completionPortThreads. The ThreadPool class manages its number dynamically based on the system workload. Methods like ThreadPool.SetMinThreads and ThreadPool.GetAvailableThreads allow you to indirectly influence the minimum number of worker and completion port threads, but there's no separate control for each type.

Who Uses the ThreadPool in C#?
The ThreadPool is a fundamental mechanism in C# for efficiently managing threads. It provides a pool of worker threads that can be reused by various parts of your application, including:

• Task Parallel Library (TPL): When you create Task or Task<TResult> objects, the TPL typically schedules them to run on ThreadPool threads by default. This enables parallel execution of tasks without the need to explicitly manage threads.
• Asynchronous Programming: Asynchronous operations like those using the async and await keywords often rely on the ThreadPool to execute the actual work in the background while the main thread remains responsive.
• Parallel Programming: Libraries like the Parallel For loop (Parallel.For) and PLINQ (Parallel LINQ) often leverage the ThreadPool to distribute work items across multiple threads.

Benefits of Using the ThreadPool

• Reduced Thread Creation Overhead: Creating threads can be expensive. The ThreadPool eliminates this overhead by creating a pool of threads upfront and reusing them as needed.
• Improved Performance: By efficiently managing threads, the ThreadPool can enhance the responsiveness and throughput of your application, especially when dealing with concurrent tasks.
• Simplified Thread Management: The ThreadPool handles thread creation, destruction, and idle thread management, freeing you from these complexities.

When to consider alternatives

• Long-Running Operations: If your work items are long-running (e.g., several seconds or more), use dedicated threads or the TaskFactory.StartNew method with a custom thread creation option might be more suitable to avoid saturating the ThreadPool and affecting overall application performance.
• Specialized Thread Requirements: If your tasks require specific thread priority or affinity, you might need to create dedicated threads with the desired settings.

Conclusion
The ThreadPool is a valuable tool for concurrent programming in C#. It offers a convenient and efficient way to manage threads, especially for short-lived, CPU-bound tasks. By understanding how the ThreadPool works and its appropriate use cases, you can create well-structured and performant C# applications.

The five SOLID design principles in object-oriented programming are intended to improve the readability, flexibility, and maintainability of software systems. We'll go into great detail about each SOLID principle in this blog article, using.NET Core examples.

1. The principle of single responsibility (SRP)
According to the Single Responsibility Principle, a class should only have one duty or responsibility, or one cause to change.

As an illustration
Take into consideration the User class, which manages emailing people and storing user data in a database. Due to the class's various responsibilities, this violates the SRP.

Bad Example
public class User
{
    public void Save()
    {
        // Saving user to the database
    }

    public void SendEmail()
    {
        // Sending email to the user
    }
}

Good Example
public class User
{
    public void Save()
    {
        // Saving user to the database
    }
}

public class EmailService
{
    public void SendEmail(User user)
    {
        // Sending email to the user
    }
}

2. Open/Closed Principle (OCP)
The Open/Closed Principle states that software entities should be open for extension but closed for modification. This means that classes should be designed in a way that allows new functionality to be added without changing existing code.

Example
Consider a class Area Calculator that calculates the area of shapes. Initially, it only supports rectangles. To adhere to the OCP, we can refactor the code to allow adding new shapes without modifying the existing AreaCalculator class.

Bad Example
public class Rectangle
{
    public double Width { get; set; }
    public double Height { get; set; }
}

public class AreaCalculator
{
    public double CalculateArea(Rectangle[] shapes)
    {
        double area = 0;

        foreach (var shape in shapes)
        {
            area += shape.Width * shape.Height;
        }

        return area;
    }
}

Good Example
public abstract class Shape
{
    public abstract double Area();
}

public class Rectangle : Shape
{
    public double Width { get; set; }
    public double Height { get; set; }

    public override double Area()
    {
        return Width * Height;
    }
}

public class AreaCalculator
{
    public double CalculateArea(Shape[] shapes)
    {
        double area = 0;

        foreach (var shape in shapes)
        {
            area += shape.Area();
        }

        return area;
    }
}

3. Liskov Substitution Principle (LSP)
The Liskov Substitution Principle states that objects of a superclass should be replaceable with objects of its subclasses without affecting the correctness of the program.

Example
Consider a Rectangle class and a Square class where a Square inherits from Rectangle. Violating the LSP would mean that substituting a Square object for a Rectangle object could lead to unexpected behavior.

Bad Example
public class Rectangle
{
    public virtual double Width { get; set; }
    public virtual double Height { get; set; }
}

public class Square : Rectangle
{
    private double _side;

    public override double Width
    {
        get => _side;
        set
        {
            _side = value;
            Height = value;
        }
    }

    public override double Height
    {
        get => _side;
        set
        {
            _side = value;
            Width = value;
        }
    }
}

Good Example
public abstract class Shape
{
    public abstract double Area();
}

public class Rectangle : Shape
{
    public double Width { get; set; }
    public double Height { get; set; }

    public override double Area()
    {
        return Width * Height;
    }
}

public class Square : Shape
{
    public double Side { get; set; }

    public override double Area()
    {
        return Side * Side;
    }
}

4. Interface Segregation Principle (ISP)
The Interface Segregation Principle states that clients should not be forced to depend on interfaces they don’t use. It emphasizes breaking interfaces into smaller, more specific ones.

Example
Consider an IWorker interface that contains both Work() and TakeBreak() methods. This forces all implementing classes to implement both methods, even if they don’t need them.

Bad Example
public interface IWorker
{
    void Work();
    void TakeBreak();
}

public class Programmer : IWorker
{
    public void Work()
    {
        // Programming tasks
    }

    public void TakeBreak()
    {
        // Taking a break
    }
}

Good Example
public interface IWorker
{
    void Work();
}

public interface IBreakable
{
    void TakeBreak();
}

public class Programmer : IWorker, IBreakable
{
    public void Work()
    {
        // Programming tasks
    }

    public void TakeBreak()
    {
        // Taking a break
    }
}

5. Dependency Inversion Principle (DIP)
The Dependency Inversion Principle states that high-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions.

Example
Consider a UserManager class that directly depends on a Logger class. This creates a tight coupling between the two classes, making it difficult to change the logging implementation.

Bad Example
public class Logger
{
    public void Log(string message)
    {
        // Logging implementation
    }
}

public class UserManager
{
    private Logger _logger;

    public UserManager()
    {
        _logger = new Logger();
    }
}

Good Example
public interface ILogger
{
    void Log(string message);
}

public class Logger : ILogger
{
    public void Log(string message)
    {
        // Logging implementation
    }
}

public class UserManager
{
    private ILogger _logger;

    public UserManager(ILogger logger)
    {
        _logger = logger;
    }
}

Conclusion
You can produce software architectures that are more flexible, scalable, and maintainable by comprehending and implementing the SOLID principles in your.NET Core applications. Writing clear, modular, and testable code is made easier by following these guidelines, which eventually improves software quality and developer efficiency.