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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