1. 数据类型#

• 值类型：int, double, bool, struct, enum • 引用类型：class, interface, delegate, object, string • 可空类型：int? nullableInt = null;

2. 变量与常量#

int num = 10;           // 变量
const double PI = 3.14; // 常量
var name = "C#";        // 类型推断

3. 控制结构#

// 条件语句
if (condition) { ... }
switch (value) { case 1: ... break; }

// 循环
for (int i = 0; i < 10; i++) { ... }
foreach (var item in list) { ... }
while (condition) { ... }

4. 函数#

int Add(int a, int b) => a + b; // 表达式体方法
void Log(string message) { ... }

5. 命名空间#

namespace MyApp;

1. 类与对象#

public class Person
{
    // 属性（自动实现）
    public string Name { get; set; } 

    // 构造函数
    public Person(string name) => Name = name;

    // 方法
    public void SayHello() => Console.WriteLine($"Hello, {Name}");
}

2. 继承与多态#

public class Student : Person
{
    public Student(string name) : base(name) { }
    public override void SayHello() => Console.WriteLine("Hi, I'm a student!");
}

3. 接口与抽象类#

public interface IDrawable
{
    void Draw();
}

public abstract class Shape : IDrawable
{
    public abstract void Draw(); // 抽象方法
}

4. 结构体与枚举#

public struct Point { public int X; public int Y; }
public enum Color { Red, Green, Blue }

5. 访问修饰符#

• public, private, protected, internal, protected internal

1. 委托与事件#

public delegate void MyDelegate(string msg);
public event MyDelegate OnMessage;

// Lambda 表达式
Action<string> print = msg => Console.WriteLine(msg);
Func<int, int, int> add = (a, b) => a + b;

2. LINQ（语言集成查询）#

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var evenNumbers = from num in numbers where num % 2 == 0 select num;
var squares = numbers.Select(n => n * n);

3. 异步编程#

public async Task<string> FetchDataAsync()
{
    using var client = new HttpClient();
    return await client.GetStringAsync("https://example.com");
}

4. 泛型#

public class Box<T>
{
    public T Content { get; set; }
}

5. 反射与特性#

[Serializable]
public class DataModel { }

// 反射获取类型信息
Type type = typeof(DataModel);
var attributes = type.GetCustomAttributes();

6. 异常处理#

try { ... }
catch (IOException ex) when (ex.Message.Contains("file")) { ... }
finally { ... }

1. 依赖注入（.NET Core）#

var services = new ServiceCollection();
services.AddSingleton<ILogger, ConsoleLogger>();
var provider = services.BuildServiceProvider();
var logger = provider.GetService<ILogger>();

2. 异步流（C# 8+）#

public async IAsyncEnumerable<int> GenerateNumbersAsync()
{
    for (int i = 0; i < 10; i++)
    {
        await Task.Delay(100);
        yield return i;
    }
}

3. 模式匹配（C# 9+）#

var result = obj switch
{
    int i when i > 0 => "Positive",
    string s => $"String: {s}",
    _ => "Unknown"
};

4. 记录类型（C# 9+）#

public record Person(string Name, int Age);
var person = new Person("Alice", 30);
var updated = person with { Age = 31 };