设计模式系列 - 观察者模式

当对象之间存在一对多的关系时，若需要进行对象之间的通知，则可使用观察者模式

介绍#

观察者模式属于行为型模式，当一个对象的状态发生改变时，若我们想通知其他对象，此时可通过观察者模式来进行解决。

类图描述#

代码实现#

1、定义抽象观察者

public abstract class Observer
{
    protected Subject subject;
    public abstract void Update();
}

2、定义观察者管理类

public class Subject
{
    private List<Observer> observers = new List<Observer>();

    private int state;
    public int GetState() => this.state;

    public void SetState(int state)
    {
        this.state = state;
        NitifyAllObservers();
    }

    public void Attach(Observer observer)
    {
        observers.Add(observer);
    }

    private void NitifyAllObservers()
    {
        foreach (var observer in observers)
        {
            observer.Update();
        }
    }
}

3、定义具体观察者

public class BinaryObserver : Observer
{
    public BinaryObserver(Subject subject)
    {
        this.subject = subject;
        this.subject.Attach(this);
    }

    public override void Update()
    {
        Console.WriteLine($"Binary string:{subject.GetState()}");
    }
}

public class HexaObserver:Observer
{
    public HexaObserver(Subject subject)
    {
        this.subject = subject;
        this.subject.Attach(this);
    }

    public override void Update()
    {
        Console.WriteLine($"Hex string:{subject.GetState()}");
    }
}

public class OctalObserver:Observer
{
    public OctalObserver(Subject subject)
    {
        this.subject = subject;
        this.subject.Attach(this);
    }

    public override void Update()
    {
        Console.WriteLine($"Octal string:{subject.GetState()}");

    }
}

4、上层调用

class Program
{
    static void Main(string[] args)
    {
        Subject subject = new Subject();

        new HexaObserver(subject);
        new OctalObserver(subject);
        new BinaryObserver(subject);
        Console.WriteLine("First state change:15");
        subject.SetState(15);
        Console.WriteLine("Second state change:10");
        subject.SetState(10);

        Console.ReadKey();
    }
}