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}");
        }
    }
}