C#如何从自定义事件中清除处理程序

public class CustomEventArgs : EventArgs
{
    public string Message { get; set; }
}

public class EventPublisher
{
    // 定义一个委托
    public delegate void CustomEventHandler(object sender, CustomEventArgs e);

    // 定义一个事件
    public event CustomEventHandler CustomEvent;

    protected virtual void OnCustomEvent(CustomEventArgs e)
    {
        CustomEvent?.Invoke(this, e);
    }

    public void RaiseEvent()
    {
        OnCustomEvent(new CustomEventArgs { Message = "Event raised!" });
    }
}

public class EventSubscriber
{
    public void Subscribe(EventPublisher publisher)
    {
        publisher.CustomEvent += HandleCustomEvent;
    }

    public void Unsubscribe(EventPublisher publisher)
    {
        publisher.CustomEvent -= HandleCustomEvent;
    }

    private void HandleCustomEvent(object sender, CustomEventArgs e)
    {
        Console.WriteLine($"Event handled: {e.Message}");
    }
}

// 使用示例
var publisher = new EventPublisher();
var subscriber = new EventSubscriber();

subscriber.Subscribe(publisher);
publisher.RaiseEvent(); // 输出: Event handled: Event raised!

subscriber.Unsubscribe(publisher);
publisher.RaiseEvent(); // 无输出

public void ClearEventHandlers(EventPublisher publisher)
{
    publisher.CustomEvent = null;
}

protected virtual void OnCustomEvent(CustomEventArgs e)
{
    CustomEvent?.Invoke(this, e); // 使用 null 条件运算符防止 NullReferenceException
}