带有委托的C#观察者/可观察者的超简单示例
带有委托的C#观察者/可观察者的超简单示例
提问于 2009-08-08 18:04:53
我最近开始深入研究C#，但在语言中实现观察者/可观察模式时，我无法弄清楚委托是如何工作的。
谁能给我一个超级简单的例子，说明它是如何做到的？我已经用谷歌搜索过了，但我发现的所有例子要么太具体问题，要么太“臃肿”。
回答 5
Stack Overflow用户
回答已采纳
发布于 2009-08-08 18:12:49
观察者模式通常使用events实现。
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();
}
}有关更多详细信息，请参阅链接文章。
请注意，上面的示例使用C# 6 null条件运算符安全地实现DoSomething，以处理尚未订阅SomethingHappened的情况，因此为null。如果您使用的是较旧版本的C#，则需要如下代码：
public void DoSomething()
{
var handler = SomethingHappened;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}Stack Overflow用户
发布于 2009-08-08 20:19:53
我把上面几个很棒的例子(一如既往地感谢Mr. Skeet和Mr. Karlsen)组合在一起，包含了几个不同的观察值，并利用一个接口在观察者中跟踪它们，并允许观察者通过一个内部列表“观察”任意数量的观察值：
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);
}
}
}Stack Overflow用户
发布于 2014-09-21 01:21:53
/**********************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);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/1249517
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