C#: المندوبون والفعاليات

delegate int MathOp(int a, int b);

class Program
{
    static int Add(int a, int b) => a + b;
    static int Multiply(int a, int b) => a * b;

    static void Main()
    {
        MathOp op = Add;
        Console.WriteLine(op(3, 4));

        op = Multiply;
        Console.WriteLine(op(3, 4));
    }
}

7
12

delegate void NotifyHandler(string msg);

class Program
{
    static void LogToConsole(string msg) => Console.WriteLine($"Console: {msg}");
    static void LogToFile(string msg) => Console.WriteLine($"File: {msg}");
    static void LogToDb(string msg) => Console.WriteLine($"Database: {msg}");

    static void Main()
    {
        NotifyHandler handler = LogToConsole;
        handler += LogToFile;
        handler += LogToDb;

        handler("System started");

        Console.WriteLine("---");

        handler -= LogToFile;
        handler("System shutdown");
    }
}

Console: System started
File: System started
Database: System started
---
Console: System shutdown
Database: System shutdown

class Program
{
    static void Main()
    {
        Action```<string>``` greet = name => Console.WriteLine($"Hello, {name}!");
        greet("Alice");

        Action noParam = () => Console.WriteLine("Parameterless Action");
        noParam();
    }
}

Hello, Alice!
Parameterless Action

class Program
{
    static void Main()
    {
        Func`<int, int, int>` add = (a, b) => a + b;
        Console.WriteLine(add(10, 20));

        Func```<string>``` getTime = () => DateTime.Now.ToString("HH:mm:ss");
        Console.WriteLine(getTime());
    }
}

30
14:30:00

class Program
{
    static void Main()
    {
        Predicate```<int>``` isEven = n => n % 2 == 0;
        Console.WriteLine(isEven(4));
        Console.WriteLine(isEven(7));

        var numbers = new List```<int>``` { 1, 2, 3, 4, 5, 6 };
        var evens = numbers.FindAll(isEven);
        Console.WriteLine(string.Join(", ", evens));
    }
}

True
False
2, 4, 6

class Program
{
    static void Main()
    {
        Func`<int, int>` square = delegate(int x) { return x * x; };
        Console.WriteLine(square(5));

        Action```<string>``` log = delegate(string msg) { Console.WriteLine($"[LOG] {msg}"); };
        log("Anonymous method example");
    }
}

25
[LOG] Anonymous method example

class Button
{
    public event EventHandler```<string>``` OnClick;

    public void Click()
    {
        OnClick?.Invoke(this, "Button clicked");
    }
}

class Program
{
    static void Main()
    {
        var btn = new Button();
        btn.OnClick += (sender, msg) => Console.WriteLine($"Event received: {msg}");
        btn.Click();
        btn.Click();
    }
}

Event received: Button clicked
Event received: Button clicked

class NewsPublisher
{
    public event EventHandler```<string>``` OnNewsPublished;

    public void Publish(string news)
    {
        Console.WriteLine($"Publishing news: {news}");
        OnNewsPublished?.Invoke(this, news);
    }
}

class NewsSubscriber
{
    public string Name { get; }

    public NewsSubscriber(string name)
    {
        Name = name;
    }

    public void Subscribe(NewsPublisher publisher)
    {
        publisher.OnNewsPublished += HandleNews;
    }

    public void Unsubscribe(NewsPublisher publisher)
    {
        publisher.OnNewsPublished -= HandleNews;
    }

    private void HandleNews(object sender, string news)
    {
        Console.WriteLine($"  [{Name}] Received: {news}");
    }
}

class Program
{
    static void Main()
    {
        var publisher = new NewsPublisher();
        var sub1 = new NewsSubscriber("Reader A");
        var sub2 = new NewsSubscriber("Reader B");

        sub1.Subscribe(publisher);
        sub2.Subscribe(publisher);

        publisher.Publish("C# 12 officially released");

        sub2.Unsubscribe(publisher);
        publisher.Publish(".NET 9 performance improved by 50%");
    }
}

Publishing news: C# 12 officially released
  [Reader A] Received: C# 12 officially released
  [Reader B] Received: C# 12 officially released
Publishing news: .NET 9 performance improved by 50%
  [Reader A] Received: .NET 9 performance improved by 50%

class TemperatureEventArgs : EventArgs
{
    public double Temperature { get; }
    public DateTime Timestamp { get; }

    public TemperatureEventArgs(double temperature)
    {
        Temperature = temperature;
        Timestamp = DateTime.Now;
    }
}

class TemperatureMonitor
{
    public event EventHandler<TemperatureEventArgs> OnTemperatureAlert;
    private double _threshold;

    public TemperatureMonitor(double threshold)
    {
        _threshold = threshold;
    }

    public void CheckTemperature(double current)
    {
        Console.WriteLine($"Current temperature: {current}°C");
        if (current > _threshold)
        {
            var args = new TemperatureEventArgs(current);
            OnTemperatureAlert?.Invoke(this, args);
        }
    }
}

class Cooler
{
    public void StartCooling(object sender, TemperatureEventArgs e)
    {
        Console.WriteLine($"  🚨 Temperature exceeded! {e.Temperature}°C > threshold, starting cooling (time: {e.Timestamp:HH:mm:ss})");
    }
}

class Program
{
    static void Main()
    {
        var monitor = new TemperatureMonitor(30.0);
        var cooler = new Cooler();

        monitor.OnTemperatureAlert += cooler.StartCooling;

        monitor.CheckTemperature(25.0);
        monitor.CheckTemperature(32.5);
        monitor.CheckTemperature(28.0);
        monitor.CheckTemperature(35.0);
    }
}

Current temperature: 25°C
Current temperature: 32.5°C
  🚨 Temperature exceeded! 32.5°C > threshold, starting cooling (time: 14:30:00)
Current temperature: 28°C
Current temperature: 35°C
  🚨 Temperature exceeded! 35°C > threshold, starting cooling (time: 14:30:01)