19使用推模式和拉模式实现电梯超重报警

当电梯超过最大承重800公斤，报警器报警。把电梯看成被观察者，报警器看成观察者。分别使用推模式和拉模式实现超重报警。

 

  推模式实现超重报警

被观察者在运行本身方法的时候，达到一定条件，就触发通知事件，把自己的状态"推"个观察者。

→把电梯看作是被观察者，当运行其TestWeight()方法时候，如果满足某种weight变量>800，就触发方法把自己的状态推给观察者。

 //被观察者


[code] public class Elevator : SubjectBase

{

private int weight;

private static string factory = "日立";

private static string area = "广州";

  protected virtual void OnMoreThanStandard(MoreThanStandardEventArgs e)

 {

base.Notify(e);

  }

  public void TestWeight()

 {

for (int i = 795; i <= 805; i++)

  {

 weight = i;

 if (weight > 800)

{

  MoreThanStandardEventArgs e = new MoreThanStandardEventArgs(weight,factory,area);

  OnMoreThanStandard(e);

 }

}

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→Elevator把自己的状态信息封装成MoreThanStandardEventArgs类，推送给观察者。

 //观察者和被观察者之间传递的参数


[code] public class MoreThanStandardEventArgs

{

private int weight;

  private string factory;

  private string area;

  public MoreThanStandardEventArgs(int weight, string factory, string area)

 {

this.weight = weight;

this.factory = factory;

this.area = area;

  }

  public int Weight {get { return weight; }}

  public string Factory {get { return factory; }}

  public string Area {get { return area; }}

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→Elevator本身没有注册、注销、通知观察者的能力，所以需要继承有这些能力的基类SubjectBase。

//被观察者基类抽象类


[code] public abstract class SubjectBase : IObseervable

{

  private List<IObserver>  container = new List<IObserver>();

  public void Register(IObserver obj)

 {

container.Add(obj);

  }

  public void Unregister(IObserver obj)

 {

container.Remove(obj);

  }

  protected virtual void Notify(MoreThanStandardEventArgs e)

 {

foreach (IObserver observer in container)

  {

 observer.Update(e);

}

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→而IObservalble的接口就注册和取消注册2个行为。

 //被观察者接口


[code] public interface IObseervable

{

  void Register(IObserver obj);

  void Unregister(IObserver obj);

 } 

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→观察者接口拿到被观察者推来的信息，做自己的事。

 //观察者接口


[code] public interface IObserver

{

  void Update(MoreThanStandardEventArgs e);

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→观察者就把状态信息显示出来

 //观察者


[code] public class Alarm : IObserver

{

  public void Update(MoreThanStandardEventArgs e)

 {

Console.WriteLine("嘀嘀嘀：来自{0}{1}的电梯最大承重800kg，目前重量为{2}",e.Area,e.Factory,e.Weight);

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→主程序

 class Program


[code]{

  static void Main(string[] args)

 {

Elevator elevator = new Elevator();

Alarm alarm = new Alarm();

elevator.Register(alarm);

elevator.TestWeight();

Console.ReadKey();

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

结果：





 

  拉模式实现超重报警   

观察者把被观察者拉进来作为方法参数，当被观察者在运行本身方法的时候，达到一定条件，就触发通知事件，并把自己传递给观察者方法。

 

→被观察者Elevator执行方法满足条件就触发通知

 //被观察者


[code] public class Elevator : SubjectBase

{

private int weight;

private static string factory = "日立";

private static string area = "广州";

  public int Weight {get { return weight; }}

  public string Factory {get { return factory; }}

  public string Area {get { return area; }}

  protected virtual void OnMoreThanStandard()

 {

base.Notify(this);

  }

  public void TestWeight()

 {

for (int i = 795; i <= 805; i++)

  {

 weight = i;

 if (weight > 800)

{

  OnMoreThanStandard();

 }

}

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→被观察者Elevator本身没有注册、取消注册、通知观察者的能力，需要继承拥有这些能力的SubjectBase。 

 //被观察者基类


[code] public abstract class SubjectBase : IObservable

{

  List<IObserver>  container = new List<IObserver>();

  public void Register(IObserver obj)

 {

container.Add(obj);

  }

  public void Unregister(IObserver obj)

 {

container.Remove(obj);

  }

  protected virtual void Notify(IObservable obj)

 {

foreach (IObserver observer in container)

  {

 observer.Update(obj);

}

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→观察者调用自己拉进来的观察者对象获得其状态信息

 //观察者接口


[code] public interface IObserver

{

  void Update(IObservable sender);

 }

 //观察者

 public class Alarm : IObserver

{

  public void Update(IObservable sender)

 {

Elevator elevator = (Elevator)sender;

Console.WriteLine("嘀嘀嘀：来自{0}{1}的电梯最大承重800kg，目前重量为{2}", elevator.Area, elevator.Factory, elevator.Weight);

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

→ 主程序

 class Program


[code]{

  static void Main(string[] args)

 {

Elevator elevator = new Elevator();

Alarm alarm = new Alarm();

elevator.Register(alarm);

elevator.TestWeight();

Console.ReadKey();

  }

 }

[/code]

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

结果：





 

  推模式和拉模式的区别

● 推模式的好处是按需供给：观察者需要什么状态信息，被观察者就把需要的状态信息封装起来推给观察者。缺点是需要创建封装的状态信息。

● 拉模式的好处是不需要创建推送给观察者的、封装状态的信息。缺点是把被观察者的属性和方法暴露给了被观察者。

 

而微软定义的委托EventHandler则很好解决了推和拉的问题，不仅可以拿到被观察者本身，同时可以拿到观察者的状态信息：

public delegate void EventHandler(object sender, EventArgs e)

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

参考资料：

※ 《.NET之美》--张子阳,感谢写了这么好的书！