3. AopProxyAttribute AOP代理特性

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public class isingletondisplayer : form  //从form继承
 {
  private static isingletondisplayer singleton = null ;
  private static bool toclean = false ;

  protected isingletondisplayer()
  {
   this.closing += new system.componentmodel.canceleventhandler(isingletondisplayer_closing);
  }

  #region static for singleton

  #region getsingleton
  public static isingletondisplayer getsingleton()
  {
   if(isingletondisplayer.singleton != null)
   {
    isingletondisplayer.singleton.visible = true ;
   }
   return isingletondisplayer.singleton ;
  }

  #endregion

  #region recreatesingleton

  //formonui存在是因为窗体只能在主线程（ui线程）中创建。
  public static void recreatesingleton(type targettype ,object[] args , form formonui)
  {
   type suptype = typeof(isingletondisplayer) ;
   if(! suptype.isassignablefrom(targettype))
   {
    throw new exception("target type is not derived from isingletondisplayer !") ;
   }

   if(formonui.invokerequired)
   {
    object[] paras = {targettype ,args ,formonui} ;
    formonui.invoke(new cbackcreateform(isingletondisplayer.recreatesingleton) ,paras) ;
   }
   else
   {
    try
    {
     isingletondisplayer.toclean = false ;
     isingletondisplayer.singleton  = (isingletondisplayer)activator.createinstance(targettype ,args) ;
     isingletondisplayer.singleton.visible = false ;
    }
    catch(exception ee)
    {
     throw ee ;
    }
   }
  }
  #endregion

  #region destroysingleton
  public static void destroysingleton()
  {
   isingletondisplayer.toclean = true ;
   if(isingletondisplayer.singleton != null)
   {
    isingletondisplayer.singleton.close() ;
    isingletondisplayer.singleton = null ;
   }
  }
  #endregion

  #endregion

  #region isingletondisplayer_closing
  private void isingletondisplayer_closing(object sender, system.componentmodel.canceleventargs e)
  {
   if(! isingletondisplayer.toclean)
   {
    this.visible = false ;
    e.cancel = true ;
    return ;
   }
  }
  #endregion
 }

 internal delegate void cbackcreateform(type targettype ,object[] args  , form formonui) ;

  * 使用方法：
  * 如果一个displayer需要以singleton模式呈现，那么可以先以常规的方式设计displayer，设计过程中不需要涉及任何与单件
  * 相关的东西。设计完后，只要将displayer的基类由form改为isingletondisplayer即可。接下来即可以单件的模式使用displayer了。
  *
  * 如：
  * public class appserversinfoform2 : isingletondisplayer{}
  * object[] args = {obj} ;
  * isingletondisplayer.recreatesingleton(typeof(appserversinfoform2) ,args ,formonui) ;
    
 

上面的实现很容易理解，但是上面的实现有一个弊病，因为所有的单件窗体都要公用一个静态的isingletondisplayer singleton 成员，所以一个应用程序中只能有一个单件继承自isingletondisplayer。/ 在vs2005中可以使用泛型突破此限制。 

下面在看看在vs2005中的实现。

 public class isingletondisplayer<t> : form
 {
  private static isingletondisplayer<t> singleton = null ;
  private static bool toclean = false ;

  protected isingletondisplayer()
  {
   this.closing += new system.componentmodel.canceleventhandler(isingletondisplayer_closing);
  }

  public static isingletondisplayer<t> getsingleton()
  {
   if(isingletondisplayer<t>.singleton != null)
   {
    isingletondisplayer<t>.singleton.visible = true ;
   }
   return isingletondisplayer<t>.singleton ;
  }

  public static void recreatesingleton(type targettype ,object[] args , form formonui)
  {
   type suptype = typeof(isingletondisplayer) ;
   if(! suptype.isassignablefrom(targettype))
   {
    throw new exception("target type is not derived from isingletondisplayer<t> !") ;
   }

   if(formonui.invokerequired)
   {
    object[] paras = {targettype ,args ,formonui} ;
    formonui.invoke(new cbackcreateform(isingletondisplayer<t>.recreatesingleton) ,paras) ;
   }
   else
   {
    try
    {
     isingletondisplayer<t>.toclean = false ;
     isingletondisplayer<t>.singleton  = (isingletondisplayer<t>)activator.createinstance(targettype ,args) ;
     isingletondisplayer<t>.singleton.visible = false ;
    }
    catch(exception ee)
    {
     throw ee ;
    }
   }
  }

  public static void destroysingleton()
  {
   isingletondisplayer<t>.toclean = true ;
   if(isingletondisplayer<t>.singleton != null)
   {
    isingletondisplayer<t>.singleton.close() ;
    isingletondisplayer<t>.singleton = null ;
   }
  } 
  
  private void isingletondisplayer_closing(object sender, system.componentmodel.canceleventargs e)
  {
   if(! isingletondisplayer<t>.toclean)
   {
    this.visible = false ;
    e.cancel = true ;
    return ;
   }
  }
 
    }
 

    internal delegate void cbackcreateform(type targettype ,object[] args  , form formonui) ;

    如：
    public class appserversinfoform2 : isingletondisplayer<appserversinfoform2>{}
    object[] args = {obj} ;
    isingletondisplayer<appserversinfoform2>.recreatesingleton(typeof(appserversinfoform2) ,args ,this) ;

这样每个单件都有自己的静态实例，就不会相互干扰了。

如果你有更好的实现方法，欢迎和我讨论