Java快速转C#的简明教程

// 静态类：扩展方法容器
public static class StringExtensions {
    // 扩展 string 类型的方法
    public static bool IsNullOrEmpty(this string str) {
        return string.IsNullOrEmpty(str);
    }
}

string name = null;

// 调用扩展方法（如同实例方法）
if (name.IsNullOrEmpty()) {
    Console.WriteLine("Name is null or empty");
}

Person person = GetPerson(); // 可能为 null

// 安全访问属性和方法
int length = person?.Name?.Length ?? 0;
person?.SayHello();

string name = null;
string displayName = name ?? "Guest"; // 如果 name 为 null，则使用 "Guest"

string message = GetMessage();
message ??= "Default Message"; // 如果 GetMessage() 返回 null，则赋值为默认值

string name = GetName()!; // 告诉编译器 GetName() 返回值不为 null

public class Person {
    // 字段
    private string name;

    // 属性（推荐封装字段）
    public string Name {
        get { return name; }
        set { name = value; }
    }

    // 构造函数
    public Person(string name) {
        this.name = name;
    }

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

// 继承
public class Student : Person {
    public Student(string name) : base(name) {}
}

// 接口
public interface IRunnable {
    void Run();
}

public class Car : IRunnable {
    public void Run() {
        Console.WriteLine("Car is running");
    }
}

// 委托（类似 Java 的函数式接口）
// 定义一个名为 Notify 的委托类型，它表示一种方法模板，要求方法返回 void 并接受一个 string 参数
// 类比 Java ：类似 Java 中的函数式接口（如 Consumer<String>），但 C# 的委托更直接，可以直接绑定方法。
public delegate void Notify(string message);

// 事件
public class EventPublisher {
	// 声明一个事件 OnNotify，其类型是 Notify 委托。事件本质上是委托的安全封装，外部只能通过 +=/-= 订阅/取消订阅，不能直接调用（如 OnNotify.Invoke() 会报错）。
    public event Notify OnNotify;

	// 调用 OnNotify?.Invoke(...) 触发事件，?. 是空值保护操作符（避免空引用异常）。只有当至少有一个订阅者时，才会执行。
    public void TriggerEvent() {
        OnNotify?.Invoke("Event triggered!");
    }
}

// 使用
EventPublisher publisher = new EventPublisher();
publisher.OnNotify += (msg) => Console.WriteLine(msg);
publisher.TriggerEvent();

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var even = numbers.Where(n => n % 2 == 0).ToList();

public async Task DownloadDataAsync() {
    var client = new HttpClient();
    var data = await client.GetStringAsync("https://example.com");
    Console.WriteLine(data);
}

Parallel.Invoke(() => {
   // 并行执行CPU密集任务
});

// 文件：Program.cs
using System;
namespace MyApplication;

class Program {
    static void Main(string[] args) {
        Console.WriteLine("Hello World!");
    }
}

// 通过类型名获取
Type type = typeof(string);

// 通过对象获取
object obj = new Person();
Type type = obj.GetType();

Type type = typeof(Person);

// 获取所有属性
PropertyInfo[] properties = type.GetProperties();

// 获取特定方法
MethodInfo method = type.GetMethod("SayHello");

// 获取所有字段
FieldInfo[] fields = type.GetFields();

object person = Activator.CreateInstance(typeof(Person));

MethodInfo method = type.GetMethod("SayHello");
method.Invoke(person, null);

PropertyInfo prop = type.GetProperty("Name");
prop.SetValue(person, "Alice");
string name = (string)prop.GetValue(person);

FieldInfo field = type.GetField("age", BindingFlags.NonPublic | BindingFlags.Instance);
field.SetValue(person, 30);
int age = (int)field.GetValue(person);

Assembly assembly = Assembly.GetExecutingAssembly();
foreach (Type type in assembly.GetTypes()) {
    Console.WriteLine(type.Name);
}

Assembly assembly = Assembly.LoadFile("path/to/MyLibrary.dll");
Type type = assembly.GetType("MyNamespace.MyClass");
object instance = Activator.CreateInstance(type);
MethodInfo method = type.GetMethod("DoSomething");
method.Invoke(instance, null);

dynamic person = new ExpandoObject();
person.Name = "Bob";
person.SayHello = new Action(() => Console.WriteLine("Hello"));
person.SayHello(); // 无需反射即可调用

Func<object> factory = Expression.Lambda<Func<object>>(
    Expression.New(typeof(Person))
).Compile();
object person = factory();

# 安装包
dotnet add package Newtonsoft.Json

# 更新包
dotnet add package Newtonsoft.Json --version 13.0.1

# 卸载包
dotnet remove package Newtonsoft.Json

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
  </ItemGroup>
</Project>

# 添加私有源
dotnet nuget add source https://mycompany.com/nuget -n MyCompany

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Reference Include="MyLibrary">
      <HintPath>..\Libraries\MyLibrary.dll</HintPath>
    </Reference>
  </ItemGroup>
</Project>

<ContentWithTargetPath Include="..\Libraries\MyLibrary.dll">
  <TargetPath>MyLibrary.dll</TargetPath>
  <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</ContentWithTargetPath>

using System.Runtime.InteropServices;

[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);

MessageBox(IntPtr.Zero, "Hello from C#", "Greeting", 0);

[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type);

// 调用
MessageBox(IntPtr.Zero, "Hello from C#", "Greeting", 0);

[DllImport("kernel32.dll")]
public static extern uint GetTickCount();

// 调用
uint tickCount = GetTickCount();
Console.WriteLine($"System uptime: {tickCount} ms");

[DllImport("gdi32.dll", CharSet = CharSet.Auto)]
public static extern IntPtr CreateDC(string lpszDriver, string lpszDevice, string lpszOutput, IntPtr lpInitData);

// 调用
IntPtr hdc = CreateDC("DISPLAY", null, null, IntPtr.Zero);

[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
    public int Left;
    public int Top;
    public int Right;
    public int Bottom;
}

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);

// 使用
RECT rect;
bool success = GetWindowRect(hWnd, out rect);
if (success)
{
    Console.WriteLine($"Window Rect: {rect.Left}, {rect.Top}, {rect.Right}, {rect.Bottom}");
}

using System;
using System.Runtime.InteropServices;

public static class Win32Api
{
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type);

    [DllImport("kernel32.dll")]
    public static extern uint GetTickCount();

    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
    }

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
}

// 使用
class Program
{
    static void Main()
    {
        // 调用 MessageBox
        Win32Api.MessageBox(IntPtr.Zero, "Hello from C#", "Greeting", 0);

        // 获取系统运行时间
        uint tickCount = Win32Api.GetTickCount();
        Console.WriteLine($"System uptime: {tickCount} ms");

        // 获取窗口位置
        Win32Api.RECT rect;
        bool success = Win32Api.GetWindowRect(new IntPtr(0x123456), out rect);
        if (success)
        {
            Console.WriteLine($"Window Rect: {rect.Left}, {rect.Top}, {rect.Right}, {rect.Bottom}");
        }
    }
}