C# 中的委托与事件机制详解

// 定义一个委托
public delegate void PrintDelegate(string message);
// 使用委托
public class Printer
{
    public void PrintMessage(PrintDelegate printDelegate, string message)
    {
        printDelegate(message);  // 调用委托
    }
}
public class Program
{
    public static void PrintToConsole(string message)
    {
        Console.WriteLine(message);
    }
    public static void Main()
    {
        Printer printer = new Printer();
        PrintDelegate printDelegate = PrintToConsole;  // 将方法赋值给委托
        printer.PrintMessage(printDelegate, "Hello, Delegates!");  // 输出：Hello, Delegates!
    }
}
 

PrintDelegate printDelegate = delegate (string message)
{
    Console.WriteLine(message);
};
printDelegate("Hello, Anonymous Methods!");  // 输出：Hello, Anonymous Methods!
 

PrintDelegate printDelegate = (message) => Console.WriteLine(message);
printDelegate("Hello, Lambda Expressions!");  // 输出：Hello, Lambda Expressions!
 

public class Button
{
    // 定义一个事件
    public event EventHandler Click;
    public void OnClick()
    {
        if (Click != null)
        {
            Click(this, EventArgs.Empty);  // 触发事件
        }
    }
}
public class Program
{
    public static void ButtonClicked(object sender, EventArgs e)
    {
        Console.WriteLine("Button clicked!");
    }
    public static void Main()
    {
        Button button = new Button();
        button.Click += ButtonClicked;  // 订阅事件
        button.OnClick();  // 输出：Button clicked!
    }
}
 

public delegate void NotifyDelegate(string message);
public class Program
{
    public static void PrintToConsole(string message)
    {
        Console.WriteLine($"Console: {message}");
    }
    public static void PrintToFile(string message)
    {
        Console.WriteLine($"File: {message} (simulated)");
    }
    public static void Main()
    {
        NotifyDelegate notifyDelegate = PrintToConsole;
        notifyDelegate += PrintToFile;  // 添加另一个方法
        notifyDelegate("Multicast Delegate Example");
        // 输出：
        // Console: Multicast Delegate Example
        // File: Multicast Delegate Example (simulated)
    }
}