Some common C# interview questions and answer summary

Question 1: Please explain what the delegate is in C#?

Answer: Delegate is a type used to encapsulate methods that allow us to pass methods as parameters and can call these methods at runtime. Delegation is a type-safe function pointer, which can be regarded as an abstraction of a function. It defines a signature, and any method that conforms to this signature can be referenced by a delegate.

Question 2: How to implement multi-threaded programming in C#?

Answer: In C#, multithreaded programming can be implemented in many ways, such as usingIn namespaceThreadclass, or useTaskClass andasync/awaitKeywords.

useThreadkind:

Thread myThread = new Thread(() =&gt; {
    // Actions performed});
();

useTaskClass andasync/await：

Task myTask = (() =&gt; {
    // Actions performed});

Question 3: Please explain how events (Event) in C# work?

Answer: Events are special delegates used to notify other classes that some events have occurred in the class. Events allow classes to communicate in a loosely coupled manner. A class defines an event that can trigger when a specific situation occurs. Other classes can subscribe to this event and provide handlers to respond to the event.

Question 4: How to use C# for exception handling?

Answer: In C#, exception handling is usually usedtry、catch、finallyandthrowKeywords.

try
{
    // Code that may throw exceptions}
catch (ExceptionType1 ex1)
{
    // Handle specific types of exceptions}
catch (ExceptionType2 ex2)
{
    // Handle another type of exception}
catch (Exception ex)
{
    // Handle all other types of exceptions}
finally
{
    // Clean up the code and execute it regardless of whether an exception occurs or not}

Question 5: How to implement asynchronous programming in C#?

Answer: C# providesasyncandawaitKeywords to simplify asynchronous programming. Using these keywords, you can create an asynchronous method that will release the thread when waiting for the asynchronous operation to complete, allowing the thread to handle other tasks.

public async Task MyAsyncMethod()
{
    // Use the await keyword to wait for asynchronous operation    var result = await SomeAsyncOperation();
    // Processing results}

Question 6: Please explain what LINQ is and what scenarios is it usually used for?

Answer:LINQ (Language Integrated Query) is part of C#, which allows developers to query data sources using SQL-like syntax. LINQ is usually used to process data sources such as collections, databases, XML, etc. It provides declarative data query and operation capabilities, simplifying the writing of data operation code.

Question 7: How to deal with memory management in C#?

Answer: Memory management in C# mainly relies on the garbage collector (GC) to automatically process it. However, developers still need to pay attention to the following points:

Avoid unnecessary object allocation.
useusingstatement orIDisposableInterface to free unmanaged resources.
Ensure that object references that are no longer used are released in time to help GC recycle memory in time.

Question 8: How to implement image processing and computer vision functions in C#?

Answer: In C#, a variety of libraries can be used to implement image processing and computer vision functions, such as:

Emgu CV: A cross-platform .Net packaging library that encapsulates OpenCV.
: A .NET machine learning and image processing library.
: A .NET framework for computer vision and artificial intelligence.
Hlcon: A powerful machine vision software library, widely used in the field of industrial automation.

Question 9: How to deal with image scaling in C#?

Answer: Process image scaling in C#, you can use the Graphics class and Bitmap class in the namespace. Here is a simple example showing how to scale an image:

using ;

public Bitmap ScaleImage(Bitmap originalImage, int newWidth, int newHeight)
{
    Bitmap resizedImage = new Bitmap(newWidth, newHeight);
    using (Graphics g = (resizedImage))
    {
         = .;
        (originalImage, new Rectangle(0, 0, newWidth, newHeight));
    }
    return resizedImage;
}

Question 10: How to use C# for image edge detection?

Answer: Edge detection is a basic task in computer vision. In C#, edge detection can be achieved using Emgu CV or other libraries. Here is an example of edge detection using Emgu CV:

using ;
using ;

public Image&lt;Gray, byte&gt; EdgeDetection(Image&lt;Gray, byte&gt; inputImage)
{
    Image&lt;Gray, byte&gt; edges = new Image&lt;Gray, byte&gt;(, );

    (inputImage, edges, 100, 200); // Use Canny algorithm for edge detection
    return edges;
}

Question 11: Explain how the await keyword in an asynchronous method in C# works?

Answer：awaitKeywords are used in C# to wait for the asynchronous operation to complete. When a method is marked asasync, and contains oneawaitWhen an expression is expressed, the execution of the method will beawaitPauses before the asynchronous operation of the expression is completed. During this time period, threads can be used to perform other tasks instead of being in a waiting state. Once the asynchronous operation is completed, execution will resume from the paused position.

Question 12: How to optimize the performance of C# applications?

Answer: Optimizing the performance of C# applications can be achieved in a variety of ways:

Use performance analysis tools to identify bottlenecks.
Reduce unnecessary object creation and garbage collection.
useusingStatement management resources.
Optimize data structures and algorithms.
Avoid unnecessary operations in the loop.
Use asynchronous programming to improve the responsiveness of your application.

Question 13: How to use C# to access and process Excel files?

Answer: In C#, you can useLibrary or third-party library such asEPPlus，NPOI orClosedXMLTo access and process Excel files.

useExample:

using ;

public void ReadExcelFile(string filePath)
{
    Application excelApp = new Application();
    Workbook workbook = (filePath);
    Worksheet worksheet = [1];

    Range range = ;
    for (int row = 1; row &lt;= ; row++)
    {
        for (int col = 1; col &lt;= ; col++)
        {
            // Read cell data            object cellValue = [row, col].Value;
        }
    }

    (false);
    ();
}

Examples of using third-party libraries such as EPPlus:

using OfficeOpenXml;

public void ReadExcelFile(string filePath)
{
    var package = new ExcelPackage(new FileInfo(filePath));
    ExcelWorksheet worksheet = [1];

    for (int row = 1; row &lt;= ; row++)
    {
        for (int col = 1; col &lt;= ; col++)
        {
            // Read cell data            object cellValue = [row, col].Value;
        }
    }
}

Question 14: How to implement the design pattern in C#?

Answer: Methods to implement design patterns in C# usually involve a deep understanding of object-oriented design principles and how to apply them in code. Here are some common design patterns and how to implement them in C#:

Singleton: Make sure that a class has only one instance and provides a global access point.

public sealed class Singleton
{
    private static readonly Singleton instance = new Singleton();
    public static Singleton Instance =&gt; instance;

    private Singleton() { }

    // Other methods}

Factory Method: Define an interface for creating objects, letting the subclass decide which class to instantiate.

public interface IProduct
{
    void Use();
}

public class ConcreteProductA : IProduct
{
    public void Use() { /* Implementation details */ }
}

public class ConcreteProductB : IProduct
{
    public void Use() { /* Implementation details */ }
}

public class Factory
{
    public IProduct CreateProduct(string type)
    {
        switch (type)
        {
            case "A": return new ConcreteProductA();
            case "B": return new ConcreteProductB();
            default: throw new ArgumentException();
        }
    }
}

Decorator mode: Dynamically add some extra responsibilities to the object without changing its interface.

public interface IComponent
{
    void Operation();
}

public class ConcreteComponent : IComponent
{
    public void Operation() { /* Implementation details */ }
}

public abstract class Decorator : IComponent
{
    protected IComponent component;

    public Decorator(IComponent component)
    {
         = component;
    }

    public virtual void Operation() { (); }
}

public class ConcreteDecoratorA : Decorator
{
    public ConcreteDecoratorA(IComponent component) : base(component) { }

    public override void Operation() { /* Additional operations */ (); }
}

Strategy: Define a series of algorithms, encapsulate them one by one, and make them replace each other.

public interface IStrategy
{
    int DoOperation(int num1, int num2);
}

public class ConcreteStrategyA : IStrategy
{
    public int DoOperation(int num1, int num2) { return num1 + num2; }
}

public class ConcreteStrategyB : IStrategy
{
    public int DoOperation(int num1, int num2) { return num1 - num2; }
}

public class Context
{
    private IStrategy strategy;

    public Context(IStrategy strategy)
    {
         = strategy;
    }

    public void SetStrategy(IStrategy strategy)
    {
         = strategy;
    }

    public int ExecuteStrategy(int num1, int num2)
    {
        return (num1, num2);
    }
}

Observer mode (Observer): When an object's state changes, all its dependants will automatically receive notifications.

public interface IObserver
{
    void Update();
}

public interface ISubject
{
    void Attach(IObserver observer);
    void Detach(IObserver observer);
    void Notify();
}

public class ConcreteSubject : ISubject
{
    private List&lt;IObserver&gt; observers = new List&lt;IObserver&gt;();

    public void Attach(IObserver observer)
    {
        (observer);
    }

    public void Detach(IObserver observer)
    {
        (observer);
    }

    public void Notify()
    {
        foreach (IObserver observer in observers)
        {
            ();
        }
    }

    // Method to modify the status}

public class ConcreteObserver : IObserver
{
    private ConcreteSubject subject;

    public ConcreteObserver(ConcreteSubject subject)
{
 = subject;
(this);
}

   public void Update()
   {
       // Update operation, based on the state changes of subject       ("Observer updated.");
   }
}

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