c#使用WeakReference实现简单的发布和订阅者模式

// WeakMulticastDelegate 实现
public class WeakMulticastDelegate
{
    private List<WeakReference<Action>> _delegates = new List<WeakReference<Action>>();

    // 添加委托
    public void Add(Action handler)
    {
        _delegates.Add(new WeakReference<Action>(handler));
    }

    // 移除委托
    public void Remove(Action handler)
    {
        _delegates.RemoveAll(wr =>
        {
            if (wr.TryGetTarget(out var target))
            {
                return target == handler;
            }
            return false;
        });
    }

    // 调用委托
    public void Invoke()
    {
        for (int i = _delegates.Count - 1; i >= 0; i--)
        {
            if (_delegates[i].TryGetTarget(out var target))
            {
                target(); // 调用委托方法
            }
            else
            {
                _delegates.RemoveAt(i); // 移除已被回收的委托
            }
        }
    }
}

// 事件源
public class EventSource
{
    public WeakMulticastDelegate OnEvent = new WeakMulticastDelegate();

    public void TriggerEvent()
    {
        Console.WriteLine("Event triggered!");
        OnEvent.Invoke(); // 触发事件
    }
}

// 订阅者
public class Subscriber
{
    public string Name { get; set; }

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

    public void HandleEvent()
    {
        Console.WriteLine($"{Name} handled the event!");
    }
}

// 测试程序
public class Program
{
    public static void Main()
    {
        // 创建事件源
        var eventSource = new EventSource();

        // 创建订阅者
        var subscriber1 = new Subscriber("Subscriber 1");
        var subscriber2 = new Subscriber("Subscriber 2");

        // 订阅事件
        eventSource.OnEvent.Add(subscriber1.HandleEvent);
        eventSource.OnEvent.Add(subscriber2.HandleEvent);

        // 触发事件
        eventSource.TriggerEvent();

        // 销毁一个订阅者
        subscriber1 = null;
        GC.Collect(); // 强制垃圾回收

        Console.WriteLine("After destroying Subscriber 1:");

        // 再次触发事件
        eventSource.TriggerEvent(); // 只有 Subscriber 2 会处理事件
    }
}