c# 实现观察者模式

说明：主要参考《head first设计模式(中文版)》，使用c#代码实现。

代码：github

1、观察者模式uml图

2、气象监测类图

3、气象监测代码(书中c#版)

3.1 observer

public interface iobserver
{
    void update(float temperature, float humidity, float pressure);
}

public interface idisplayelement
{
    void display();
}

public class currentconditiondisplay : iobserver, idisplayelement
{
    private readonly isubject _weatherdata;
 
    private float _temperature;
    private float _humidity;
 
    public currentconditiondisplay(isubject weatherdata)
    {
        _weatherdata = weatherdata;
        _weatherdata?.registerobserver(this);
    }
 
    public void update(float temperature, float humidity, float pressure)
    {
        _temperature = temperature;
        _humidity = humidity;
        display();
    }
 
    public void display()
    {
        console.writeline($"current conditions: {_temperature}f degress and {_humidity}% humidity");
    }
}

3.2 subject

public interface isubject
{
    void registerobserver(iobserver o);
    void removeobserver(iobserver o);
    void notifyobservers();
}

public class weatherdata : isubject
{
    //观察者列表
    private readonly list<iobserver> _observerlist;
 
    //天气数据
    private float _temperature;
    private float _humidity;
    private float _pressure;
 
    public weatherdata()
    {
        _observerlist = new list<iobserver>();
    }
 
    /// <summary>
    /// 订阅观察者
    /// </summary>
    /// <param name="o">观察者对象</param>
    public void registerobserver(iobserver o)
    {
        _observerlist.add(o);
    }
 
    /// <summary>
    /// 移除观察者
    /// </summary>
    /// <param name="o">观察者对象</param>
    public void removeobserver(iobserver o)
    {
        if (_observerlist.contains(o))
        {
            _observerlist.remove(o);
        }
    }
 
    /// <summary>
    /// 发布数据
    /// </summary>
    public void notifyobservers()
    {
        foreach (var observer in _observerlist)
        {
            observer.update(_temperature, _humidity, _pressure);
        }
    }
 
    /// <summary>
    /// 数据发生改变
    /// </summary>
    private void measurementchanged()
    {
        notifyobservers();
    }
 
    /// <summary>
    /// 更新数据
    /// </summary>
    /// <param name="temperature">温度</param>
    /// <param name="humidity">湿度</param>
    /// <param name="pressure">气压</param>
    public void setmeasurements(float temperature, float humidity, float pressure)
    {
        _temperature = temperature;
        _humidity = humidity;
        _pressure = pressure;
        measurementchanged();
    }
}

3.3 测试代码

private static void testweatherdata()
{
    var weatherdata = new weatherdata();
    var currentconditiondisplay = new currentconditiondisplay(weatherdata);
 
    weatherdata.setmeasurements(80, 65, 30.4f);
    weatherdata.setmeasurements(82, 70, 29.2f);
    weatherdata.setmeasurements(78, 90, 29.2f);
}

4、使用c#中iobservable接口实现气象监测

4.1 辅助类/结构体

public struct weathermessage
{
    public float temperature { get; set; }
    public float humidity { get; set; }
    public float pressure { get; set; }
}
 
public class messageunknownexception : exception
{
    internal messageunknownexception()
    {
 
    }
}

4.2 iobserver具体实现

class currentconditiondisplayx : iobserver<weathermessage>, idisplayelement
{
    private idisposable _unsubscribe;
 
    private float _temperature;
    private float _humidity;
 
    public void subscribe(iobservable<weathermessage> provider)
    {
        if (provider != null)
        {
            _unsubscribe = provider.subscribe(this);
        }
    }
 
    public void unsubscribe()
    {
        _unsubscribe?.dispose();
        _unsubscribe = null;
    }
 
    public void oncompleted()
    {
        console.writeline("currentconditiondisplayx: oncompleted");
        unsubscribe();
    }
 
    public void onerror(exception error)
    {
        console.writeline("currentconditiondisplayx: onerror");
    }
 
    public void onnext(weathermessage value)
    {
        _temperature = value.temperature;
        _humidity = value.humidity;
        display();
    }
 
    public void display()
    {
        console.writeline($"current conditions: {_temperature}f degress and {_humidity}% humidity");
    }
}

4.3 iobservable具体实现

public class weatherdatax : iobservable<weathermessage>
{
    private readonly list<iobserver<weathermessage>> _observerlist;
 
    public weatherdatax()
    {
        _observerlist = new list<iobserver<weathermessage>>();
    }
 
    /// <summary>
    /// 通知提供程序：某观察程序将要接收通知。
    /// </summary>
    /// <param name="observer">要接收通知的对象。</param>
    /// <returns>使资源释放的观察程序的接口。</returns>
    public idisposable subscribe(iobserver<weathermessage> observer)
    {
        if(!_observerlist.contains(observer))
        {
            _observerlist.add(observer);
        }
        return new unsubcriber(_observerlist, observer);
    }
 
    public void setmeasurements(nullable<weathermessage> message)
    {
        foreach (var observer in _observerlist)
        {
            if (!message.hasvalue)
            {
                observer.onerror(new messageunknownexception());
            }
            else
            {
                observer.onnext(message.value);
            }
        }
    }
 
    public void endtransmission()
    {
        foreach (var observer in _observerlist.toarray())
        {
            if (_observerlist.contains(observer))
            {
                observer.oncompleted();
            }
        }
        _observerlist.clear();
    }
 
    private class unsubcriber : idisposable
    {
        private list<iobserver<weathermessage>> _observerlist;
        private iobserver<weathermessage> _observer;
 
        public unsubcriber(list<iobserver<weathermessage>> observerlist, iobserver<weathermessage> observer)
        {
            _observerlist = observerlist;
            _observer = observer;
        }
 
        public void dispose()
        {
            if (_observerlist != null && _observerlist.contains(_observer))
            {
                _observerlist.remove(_observer);
            }
        }
    }
}

4.4 测试代码

private static void testweatherdatax()
{
    var weatherdata = new weatherdatax();
    var currentconditiondisplay = new currentconditiondisplayx();
 
    currentconditiondisplay.subscribe(weatherdata);
 
    weatherdata.setmeasurements(new weathermessage()
    {
        temperature = 80,
        humidity = 65,
        pressure = 30.4f
    });
    weatherdata.setmeasurements(new weathermessage()
    {
        temperature = 82,
        humidity = 70,
        pressure = 29.2f
    });
    weatherdata.setmeasurements(new weathermessage()
    {
        temperature = 78,
        humidity = 90,
        pressure = 29.2f
    });
    weatherdata.endtransmission();
}

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