C＃观察者的超简单的例子/观察到与代表(Super-simple example of C# obs

最近，我开始挖掘到C＃，但我不能用我的生命搞清楚落实在语言观察者/可观察的模式时，代表是如何工作的。

可能有人给我它是如何做一个超级简单的例子？ 我用 Google搜索这个，但所有的我发现的例子是不是太问题特定的或过于“臃肿”。

Answer 1:

观察者模式通常与执行事件 。

下面是一个例子：

using System;

class Observable
{
    public event EventHandler SomethingHappened;

    public void DoSomething() =>
        SomethingHappened?.Invoke(this, EventArgs.Empty);
}

class Observer
{
    public void HandleEvent(object sender, EventArgs args)
    {
        Console.WriteLine("Something happened to " + sender);
    }
}

class Test
{
    static void Main()
    {
        Observable observable = new Observable();
        Observer observer = new Observer();
        observable.SomethingHappened += observer.HandleEvent;

        observable.DoSomething();
    }
}

见有更详细的链接的文章。

需要注意的是上面的例子中使用C＃6 空条件操作符来实现DoSomething安全来处理情况，案件SomethingHappened尚未订阅，因此是无效。 如果您使用的C＃的旧版本，你需要这样的代码：

public void DoSomething()
{
    var handler = SomethingHappened;
    if (handler != null)
    {
        handler(this, EventArgs.Empty);
    }
}

Answer 2:

这里有一个简单的例子：

public class ObservableClass
{
    private Int32 _Value;

    public Int32 Value
    {
        get { return _Value; }
        set
        {
            if (_Value != value)
            {
                _Value = value;
                OnValueChanged();
            }
        }
    }

    public event EventHandler ValueChanged;

    protected void OnValueChanged()
    {
        if (ValueChanged != null)
            ValueChanged(this, EventArgs.Empty);
    }
}

public class ObserverClass
{
    public ObserverClass(ObservableClass observable)
    {
        observable.ValueChanged += TheValueChanged;
    }

    private void TheValueChanged(Object sender, EventArgs e)
    {
        Console.Out.WriteLine("Value changed to " +
            ((ObservableClass)sender).Value);
    }
}

public class Program
{
    public static void Main()
    {
        ObservableClass observable = new ObservableClass();
        ObserverClass observer = new ObserverClass(observable);
        observable.Value = 10;
    }
}

注意：

• 这违反了我不从可观察脱钩观察者的规则，这也许就是这个简单的例子不够好，但要确保你不保持观察家挂您的活动那样的。 处理这种情况的方法是使ObserverClass IDisposable接口，并让.Dispose方法做在构造函数的代码相反
• 检查错误，不执行，至少一个空检查应在ObserverClass的构造函数来完成

Answer 3:

在这种模式下，你有出版商谁还会做一些逻辑和发布的“事件”。
那么出版商将派出自己的活动只为谁订阅接收特定事件的订户。

在C＃中，任何对象都可以发布一组到其他应用程序可以订阅的事件。
当发布类引发的事件，所有的订阅应用程序通知。
下图显示了这种机制。

最简单的例子可以在C＃事件和委托：

代码是自我解释，而且我已经添加了注释以清除代码。

  using System;

public class Publisher //main publisher class which will invoke methods of all subscriber classes
{
    public delegate void TickHandler(Publisher m, EventArgs e); //declaring a delegate
    public TickHandler Tick;     //creating an object of delegate
    public EventArgs e = null;   //set 2nd paramter empty
    public void Start()     //starting point of thread
    {
        while (true)
        {
            System.Threading.Thread.Sleep(300);
            if (Tick != null)   //check if delegate object points to any listener classes method
            {
                Tick(this, e);  //if it points i.e. not null then invoke that method!
            }
        }
    }
}

public class Subscriber1                //1st subscriber class
{
    public void Subscribe(Publisher m)  //get the object of pubisher class
    {
        m.Tick += HeardIt;              //attach listener class method to publisher class delegate object
    }
    private void HeardIt(Publisher m, EventArgs e)   //subscriber class method
    {
        System.Console.WriteLine("Heard It by Listener");
    }

}
public class Subscriber2                   //2nd subscriber class
{
    public void Subscribe2(Publisher m)    //get the object of pubisher class
    {
        m.Tick += HeardIt;               //attach listener class method to publisher class delegate object
    }
    private void HeardIt(Publisher m, EventArgs e)   //subscriber class method
    {
        System.Console.WriteLine("Heard It by Listener2");
    }

}

class Test
{
    static void Main()
    {
        Publisher m = new Publisher();      //create an object of publisher class which will later be passed on subscriber classes
        Subscriber1 l = new Subscriber1();  //create object of 1st subscriber class
        Subscriber2 l2 = new Subscriber2(); //create object of 2nd subscriber class
        l.Subscribe(m);     //we pass object of publisher class to access delegate of publisher class
        l2.Subscribe2(m);   //we pass object of publisher class to access delegate of publisher class

        m.Start();          //starting point of publisher class
    }
}

输出：

由听者听到它

通过LISTENER2听见了它

由听者听到它

通过LISTENER2听见了它

由听者听到它。 。 。 （无限次）

Answer 4:

我绑在一起了几个上面的很好的例子（谢谢你，一如既往，以飞碟双向先生和卡尔森先生 ），包括几个不同的观测量，并利用一个接口来跟踪它们的观察者，并允许观察员通过内部列表以“守”任意数量的观测值：

namespace ObservablePattern
{
    using System;
    using System.Collections.Generic;

    internal static class Program
    {
        private static void Main()
        {
            var observable = new Observable();
            var anotherObservable = new AnotherObservable();

            using (IObserver observer = new Observer(observable))
            {
                observable.DoSomething();
                observer.Add(anotherObservable);
                anotherObservable.DoSomething();
            }

            Console.ReadLine();
        }
    }

    internal interface IObservable
    {
        event EventHandler SomethingHappened;
    }

    internal sealed class Observable : IObservable
    {
        public event EventHandler SomethingHappened;

        public void DoSomething()
        {
            var handler = this.SomethingHappened;

            Console.WriteLine("About to do something.");
            if (handler != null)
            {
                handler(this, EventArgs.Empty);
            }
        }
    }

    internal sealed class AnotherObservable : IObservable
    {
        public event EventHandler SomethingHappened;

        public void DoSomething()
        {
            var handler = this.SomethingHappened;

            Console.WriteLine("About to do something different.");
            if (handler != null)
            {
                handler(this, EventArgs.Empty);
            }
        }
    }

    internal interface IObserver : IDisposable
    {
        void Add(IObservable observable);

        void Remove(IObservable observable);
    }

    internal sealed class Observer : IObserver
    {
        private readonly Lazy<IList<IObservable>> observables =
            new Lazy<IList<IObservable>>(() => new List<IObservable>());

        public Observer()
        {
        }

        public Observer(IObservable observable) : this()
        {
            this.Add(observable);
        }

        public void Add(IObservable observable)
        {
            if (observable == null)
            {
                return;
            }

            lock (this.observables)
            {
                this.observables.Value.Add(observable);
                observable.SomethingHappened += HandleEvent;
            }
        }

        public void Remove(IObservable observable)
        {
            if (observable == null)
            {
                return;
            }

            lock (this.observables)
            {
                observable.SomethingHappened -= HandleEvent;
                this.observables.Value.Remove(observable);
            }
        }

        public void Dispose()
        {
            for (var i = this.observables.Value.Count - 1; i >= 0; i--)
            {
                this.Remove(this.observables.Value[i]);
            }
        }

        private static void HandleEvent(object sender, EventArgs args)
        {
            Console.WriteLine("Something happened to " + sender);
        }
    }
}

Answer 5:

应用与代表和在C＃中的事件观察者模式是根据MSDN这是一个轻微的变化命名为“事件模式”。

在本文中，您会发现如何应用在C＃中的两个经典的方式，并使用委托和事件的模式以及结构化的例子。

探索Observer设计模式

public class Stock
{

    //declare a delegate for the event
    public delegate void AskPriceChangedHandler(object sender,
          AskPriceChangedEventArgs e);
    //declare the event using the delegate
    public event AskPriceChangedHandler AskPriceChanged;

    //instance variable for ask price
    object _askPrice;

    //property for ask price
    public object AskPrice
    {

        set
        {
            //set the instance variable
            _askPrice = value;

            //fire the event
            OnAskPriceChanged();
        }

    }//AskPrice property

    //method to fire event delegate with proper name
    protected void OnAskPriceChanged()
    {

        AskPriceChanged(this, new AskPriceChangedEventArgs(_askPrice));

    }//AskPriceChanged

}//Stock class

//specialized event class for the askpricechanged event
public class AskPriceChangedEventArgs : EventArgs
{

    //instance variable to store the ask price
    private object _askPrice;

    //constructor that sets askprice
    public AskPriceChangedEventArgs(object askPrice) { _askPrice = askPrice; }

    //public property for the ask price
    public object AskPrice { get { return _askPrice; } }

}//AskPriceChangedEventArgs

Answer 6:

    /**********************Simple Example ***********************/    

class Program
        {
            static void Main(string[] args)
            {
                Parent p = new Parent();
            }
        }

        ////////////////////////////////////////////

        public delegate void DelegateName(string data);

        class Child
        {
            public event DelegateName delegateName;

            public void call()
            {
                delegateName("Narottam");
            }
        }

        ///////////////////////////////////////////

        class Parent
        {
            public Parent()
            {
                Child c = new Child();
                c.delegateName += new DelegateName(print);
                //or like this
                //c.delegateName += print;
                c.call();
            }

            public void print(string name)
            {
                Console.WriteLine("yes we got the name : " + name);
            }
        }

Answer 7:

余did't想改变我的源代码添加额外的观察者，所以我写了下面这个简单的例子：

//EVENT DRIVEN OBSERVER PATTERN
public class Publisher
{
    public Publisher()
    {
        var observable = new Observable();
        observable.PublishData("Hello World!");
    }
}

//Server will send data to this class's PublishData method
public class Observable
{
    public event Receive OnReceive;

    public void PublishData(string data)
    {
        //Add all the observer below
        //1st observer
        IObserver iObserver = new Observer1();
        this.OnReceive += iObserver.ReceiveData;
        //2nd observer
        IObserver iObserver2 = new Observer2();
        this.OnReceive += iObserver2.ReceiveData;

        //publish data 
        var handler = OnReceive;
        if (handler != null)
        {
            handler(data);
        }
    }
}

public interface IObserver
{
    void ReceiveData(string data);
}

//Observer example
public class Observer1 : IObserver
{
    public void ReceiveData(string data)
    {
        //sample observers does nothing with data :)
    }
}

public class Observer2 : IObserver
{
    public void ReceiveData(string data)
    {
        //sample observers does nothing with data :)
    }
}

Answer 8:

事情是这样的：

// interface implementation publisher
public delegate void eiSubjectEventHandler(eiSubject subject);

public interface eiSubject
{
    event eiSubjectEventHandler OnUpdate;

    void GenereteEventUpdate();

}

// class implementation publisher
class ecSubject : eiSubject
{
    private event eiSubjectEventHandler _OnUpdate = null;
    public event eiSubjectEventHandler OnUpdate
    {
        add
        {
            lock (this)
            {
                _OnUpdate -= value;
                _OnUpdate += value;
            }
        }
        remove { lock (this) { _OnUpdate -= value; } }
    }

    public void GenereteEventUpdate()
    {
        eiSubjectEventHandler handler = _OnUpdate;

        if (handler != null)
        {
            handler(this);
        }
    }

}

// interface implementation subscriber
public interface eiObserver
{
    void DoOnUpdate(eiSubject subject);

}

// class implementation subscriber
class ecObserver : eiObserver
{
    public virtual void DoOnUpdate(eiSubject subject)
    {
    }
}

。 观察者模式C＃与事件 。 链接库

文章来源: Super-simple example of C# observer/observable with delegates