C# 实现简单的观察者模式

// 观察者接口
public interface IObserver
{
    void Update(string message);
}
// 主题接口
public interface ISubject
{
    void Attach(IObserver observer);
    void Detach(IObserver observer);
    void Notify(string message);
}
// 具体主题
public class NewsSubject : ISubject
{
    private readonly List<IObserver> _observers = new List<IObserver>();
    public void Attach(IObserver observer) => _observers.Add(observer);
    public void Detach(IObserver observer) => _observers.Remove(observer);
    public void Notify(string message)
    {
        foreach (var observer in _observers)
        {
            observer.Update(message);
        }
    }
}
// 具体观察者
public class UserObserver : IObserver
{
    private readonly string _userName;
    public UserObserver(string name) => _userName = name;
    public void Update(string message) => Console.WriteLine($"{_userName} 收到消息: {message}");
}
// 调用示例
public static void TestObserver()
{
    var news = new NewsSubject();
    news.Attach(new UserObserver("张三"));
    news.Attach(new UserObserver("李四"));
    news.Notify("C# 进阶教程已发布！");
}

// 策略接口
public interface ISortStrategy
{
    void Sort(List<int> list);
}
// 冒泡排序策略
public class BubbleSort : ISortStrategy
{
    public void Sort(List<int> list)
    {
        Console.WriteLine("使用冒泡排序");
        for (int i = 0; i < list.Count - 1; i++)
        {
            for (int j = 0; j < list.Count - i - 1; j++)
            {
                if (list[j] > list[j + 1])
                {
                    (list[j], list[j + 1]) = (list[j + 1], list[j]);
                }
            }
        }
    }
}
// 快速排序策略
public class QuickSort : ISortStrategy
{
    public void Sort(List<int> list)
    {
        Console.WriteLine("使用快速排序");
        QuickSortInternal(list, 0, list.Count - 1);
    }
    private void QuickSortInternal(List<int> list, int left, int right)
    {
        // 快速排序实现逻辑
    }
}
// 上下文类
public class Sorter
{
    private ISortStrategy _strategy;
    public Sorter(ISortStrategy strategy) => _strategy = strategy;
    public void SetStrategy(ISortStrategy strategy) => _strategy = strategy;
    public void SortList(List<int> list) => _strategy.Sort(list);
}
// 调用示例
public static void TestStrategy()
{
    var list = new List<int> { 3, 1, 4, 1, 5, 9 };
    var sorter = new Sorter(new BubbleSort());
    sorter.SortList(list);
    sorter.SetStrategy(new QuickSort());
    sorter.SortList(list);
}