# 观察者模式

属于行为型模式。
它定义了一种一对多的依赖关系，当一个对象的状态发生改变时，其所有依赖者都会收到通知并自动更新。

CSharp 事件就是观察者模式。接下来的演示将不会使用委托和事件，而是使用接口来实现。

# 类图

	namespace BehavioralPatterns_ObserverPattern
	{
	/// <summary>
	/// 观察者
	/// </summary>
	public interface Observer
	{
	/// <summary>
	/// 更新
	/// </summary>
	public void Update();
	}
	}

	namespace BehavioralPatterns_ObserverPattern
	{
	/// <summary>
	/// 形状
	/// </summary>
	public class Shape : Observer
	{
	public string ShapeName;
	public string ColorName;

	public Shape(string shapeName, string colorName)
	{
	ShapeName = shapeName;
	ColorName = colorName;
	}

	public void Show()
	{
	Console.WriteLine("Shape：" + ShapeName);
	Console.WriteLine("Color：" + ColorName);
	}

	public void Update()
	{
	ShapeName = "Default";
	ColorName = "Default";
	}
	}
	}

	namespace BehavioralPatterns_ObserverPattern
	{
	public class ObserverAction
	{
	/// <summary>
	/// 观察者列表
	/// </summary>
	private List<Observer> ObserverList;

	public ObserverAction()
	{
	ObserverList = new List<Observer>();
	}

	/// <summary>
	/// 添加观察者
	/// </summary>
	/// <param name="listener"></param>
	public void AddObserver(Observer observer)
	{
	ObserverList.Add(observer);
	}

	/// <summary>
	/// 移除观察者
	/// </summary>
	/// <param name="listener"></param>
	public void RemoveObserver(Observer observer)
	{
	ObserverList.Remove(observer);
	}

	/// <summary>
	/// 通知所有观察者
	/// </summary>
	public void Invoke()
	{
	foreach (var item in ObserverList)
	{
	item.Update();
	}
	}
	}
	}

	namespace BehavioralPatterns_ObserverPattern
	{
	public class Program
	{
	private static void Main()
	{
	Shape shape = new Shape("Square", "Red");

	ObserverAction observerAction = new ObserverAction();
	observerAction.AddObserver(shape);

	shape.Show();
	observerAction.Invoke();
	Console.WriteLine();
	shape.Show();
	}
	}
	}

运行结果：
Shape：Square
Color：Red

Shape：Default
Color：Default