C# .NET Interview Questions & Answers: Level Up Your Expertise

C# .NET interview questions and answers include basic knowledge, core concepts, and advanced usage. 1) Basic knowledge: C# is an object-oriented language developed by Microsoft and is mainly used in the .NET framework. 2) Core concepts: Delegation and events allow dynamic binding methods, and LINQ provides powerful query functions. 3) Advanced usage: Asynchronous programming improves responsiveness, and expression trees are used for dynamic code construction.

introduction

If you are preparing for an interview with C# .NET, or want to improve your professionalism in this field, then you are in the right place. Today we will explore some key interview questions and answers in depth, which not only help you better understand C# .NET, but also make you stand out in the interview. Through this article, you will master the basic to advanced knowledge points, and at the same time you can also learn some of the experience and skills I have accumulated in the process of using C# .NET.

Review of basic knowledge

C# is a modern, object-oriented programming language developed by Microsoft and is mainly used in the .NET framework. .NET is an open source development platform that supports a variety of programming languages ​​and libraries to help developers build various types of applications. From basic data types, classes and objects to more advanced features such as LINQ and asynchronous programming, C# .NET provides a wealth of tools and features.

When using C#, it is crucial to understand basic syntax and structure. For example, C# uses the using keyword to introduce a namespace, which helps manage the organization and readability of the code. At the same time, the garbage collection mechanism of C# makes memory management simpler and more efficient.

Core concept or function analysis

Delegation and Events in C#

Delegations and events are very important concepts in C#, which make the code more flexible and scalable. Delegates can be regarded as references to methods, while events are delegates triggered under certain conditions.

 // Define a delegate public delegate void MyDelegate(string message);

// Use delegate public class MyClass
{
    public event MyDelegate MyEvent;

    public void RaiseEvent(string message)
    {
        MyEvent?.Invoke(message);
    }
}

//Use events public class Program
{
    public static void Main()
    {
        MyClass obj = new MyClass();
        obj.MyEvent = (message) => Console.WriteLine($"Received: {message}");
        obj.RaiseEvent("Hello, World!");
    }
}

Delegates and events work in that they allow dynamic binding and unbinding methods at runtime, which makes the code more modular and maintainable. However, it is important to note that overuse of events can cause performance problems, as the subscription and unsubscribe operations of events may affect the execution efficiency of the program.

The powerful features of LINQ

LINQ (Language Integrated Query) is a very powerful query syntax in C#, which allows developers to manipulate data collections in a declarative way. LINQ can not only be used for data in memory, but also interact with databases, greatly simplifying the complexity of data processing.

 // Use LINQ to query list List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6 };
var evenNumbers = numbers.Where(n => n % 2 == 0).ToList();

// Use LINQ to interact with the database using (var context = new MyDbContext())
{
    var users = context.Users.Where(u => u.Age > 18).ToList();
}

LINQ works by delaying execution and expression trees to achieve efficient data query. Delayed execution means that queries are executed only when results are needed, which can significantly improve performance. However, abuse of LINQ can lead to difficult debugging problems, as the execution time and location of the query may not be intuitive.

Example of usage

Basic usage of asynchronous programming

Asynchronous programming is a very important feature in C#, which allows developers to write efficient non-blocking code. Asynchronous operations can be easily implemented using async and await keywords.

 public async Task<string> DownloadFileAsync(string url)
{
    using (var client = new HttpClient())
    {
        var response = await client.GetAsync(url);
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadAsStringAsync();
    }
}

The key to asynchronous programming is that it does not block the main thread, thereby improving the responsiveness and performance of the application. However, asynchronous programming also has some pitfalls, such as deadlock problems, especially when using UI threads, which require special attention.

Advanced usage: Expression tree

The expression tree is an advanced feature in C# that allows developers to build and execute code dynamically at runtime. Expression trees are very useful in ORM frameworks and dynamic queries.

 // Create an expression tree ParameterExpression param = Expression.Parameter(typeof(int), "x");
Expression body = Expression.Lambda<Func<int, bool>>(
    Expression.GreaterThan(param, Expression.Constant(5)),
    param
);

// Compile and execute the expression tree Func<int, bool> func = body.Compile();
bool result = func(10); // true

The power of an expression tree is its flexibility and dynamicity, but its complexity also makes it unsuitable for beginners. When using expression trees, you need to pay special attention to performance issues, as dynamically generating and compiling code can bring additional overhead.

Common Errors and Debugging Tips

Common errors when using C# .NET include null reference exceptions, type conversion errors, and deadlock problems in asynchronous programming. When debugging these problems, you can use Visual Studio's debugging tools such as breakpoints, monitoring windows, and call stacks to locate and resolve problems.

For example, when dealing with null reference exceptions, you can use the null condition operator ? to avoid the occurrence of exceptions:

 string name = null;
string upperName = name?.ToUpper(); // upperName will be null without throwing an exception

Performance optimization and best practices

Performance optimization is a key topic in C# .NET. When using LINQ, query performance can be improved by selecting the appropriate operator, such as using FirstOrDefault instead of First to avoid unnecessary enumerations.

 // More efficient query var firstEvenNumber = numbers.FirstOrDefault(n => n % 2 == 0);

Additionally, best practices for asynchronous programming include avoiding the use of Task.Result or Task.Wait in asynchronous methods, as these operations can cause deadlocks. Instead, await should be used to wait for the task to complete.

It is also very important to keep the code readable and maintainable when writing it. Using meaningful variable names, adding appropriate comments, and following code style guides can greatly improve the quality of your code.

Through this article, you not only master the interview questions and answers of C# .NET, but also understand many practical techniques and best practices. Hopefully this knowledge will help you perform well in interviews and be at ease in actual development.

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