Differences between revisions 18 and 19
⇤ ← Revision 18 as of 2005-07-31 15:15:14 →
Size: 5155
Editor: flyaflya
Comment:
← Revision 19 as of 2005-07-31 15:21:59 → ⇥
Size: 5163
Editor: flyaflya
Comment:
Deletions are marked like this. Additions are marked like this.
Line 102: Line 102:
例如，窗口UI对消息的处理：
 例如，窗口UI对消息的处理：[[BR]]
Line 145: Line 144:
为其他对象提供一种代理以控制对这个对象的访问。
 为其他对象提供一种代理以控制对这个对象的访问。[[BR]]

TableOfContents

设计模式

介绍

创建型模式

singleton(单件)

意图

保证一个类仅有一个实例，并提供一个访问它的全局访问点。

实现代码

Toggle line numbers 
   1 class Singleton:
   2     """ A python singleton """
   3 
   4     class __impl:
   5         """ Implementation of the singleton interface """
   6 
   7         def spam(self):
   8             """ Test method, return singleton id """
   9             return id(self)
  10 
  11     # storage for the instance reference
  12     __instance = None
  13 
  14     def __init__(self):
  15         """ Create singleton instance """
  16         # Check whether we already have an instance
  17         if Singleton.__instance is None:
  18             # Create and remember instance
  19             Singleton.__instance = Singleton.__impl()
  20 
  21         # Store instance reference as the only member in the handle
  22         self.__dict__['_Singleton__instance'] = Singleton.__instance
  23 
  24     def __getattr__(self, attr):
  25         """ Delegate access to implementation """
  26         return getattr(self.__instance, attr)
  27 
  28     def __setattr__(self, attr, value):
  29         """ Delegate access to implementation """
  30         return setattr(self.__instance, attr, value)
  31 
  32 
  33 # Test it
  34 s1 = Singleton()
  35 print id(s1), s1.spam()
  36 
  37 s2 = Singleton()
  38 print id(s2), s2.spam()
  39 
  40 # Sample output, the second (inner) id is constant:
  41 # 8172684 8176268
  42 # 8168588 8176268

另一个实现代码

从[http://members.chello.nl/f.niessink/ TaskCoach]的代码中摘抄，因此许可证为GPL。 -- QiangningHong

Toggle line numbers 
   1 class Singleton(type):
   2     """Singleton Metaclass"""
   3 
   4     def __init__(cls, name, bases, dic):
   5         super(Singleton, cls).__init__(name, bases, dic)
   6         cls.instance = None
   7 
   8     def __call__(cls, *args, **kwargs):
   9         if cls.instance is None:
  10             cls.instance = super(Singleton, cls).__call__(*args, **kwargs)
  11         return cls.instance

使用方法:

Toggle line numbers 
   1 class MyClass(object):
   2     __metaclass__ = Singleton
   3 
   4 ob1 = MyClass()
   5 ob2 = MyClass()
   6 assert ob1 is ob2

结构型模式

行为模式

Chain of Responsibility（职责链）

意图

使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。

说明

用一系列类(classes)试图处理一个请求request,这些类之间是一个松散的耦合,唯一共同点是在他们之间传递request. 也就是说，来了一个请求，A类先处理，如果没有处理，就传递到B类处理，如果没有处理，就传递到C类处理，就这样象一个链条(chain)一样传递下去。 例如，窗口UI对消息的处理：BR attachment:CORPattern.gif

代码实现

模拟UI对消息的处理

Toggle line numbers 
   1 class Event:
   2     def __init__( self, name ):
   3         self.name = name
   4 
   5 class Widget:
   6     def __init__( self, parent = None ):
   7         self.__parent = parent
   8     def Handle( self, event ):
   9         handler = 'Handle_' + event.name
  10         if hasattr( self, handler ):
  11             method = getattr( self, handler )
  12             method( event )
  13         elif self.__parent:
  14             self.__parent.Handle( event )
  15         elif hasattr( self, 'HandleDefault' ):
  16             self.HandleDefault( event )

使用： 当用一个event被Handle，将调用Handle_"event.name"，如果没有此函数就调用parent来处理此event，如果还没有被处理，就试着交给HandleDefault（）。 例如：

Toggle line numbers 
   1 class MainWindow(Widget):
   2     def Handle_close( self, event ):
   3         print 'MainWindow: ' + event.name
   4     def HandleDefault( self, event ):
   5         print 'Default: ' + event.name
   6         
   7 class Button( Widget ):
   8     def Handle_click( self, event ):
   9         print 'Button: ' + event.name

=== Proxy（代理）===

意图

为其他对象提供一种代理以控制对这个对象的访问。BR attachment:ProxyPattern.gif

代码

Toggle line numbers 
   1 class Proxy:
   2     def __init__( self, subject ):
   3         self.__subject = subject
   4     def __getattr__( self, name ):
   5         return getattr( self.__subject, name )

例子：

Toggle line numbers 
   1 class RGB:
   2     def __init__( self, red, green, blue ):
   3         self.__red = red
   4         self.__green = green
   5         self.__blue = blue
   6     def Red( self ):
   7         return self.__red
   8     def Green( self ):
   9         return self.__green
  10     def Blue( self ):
  11         return self.__blue

使用Proxy改变Blue函数：

Toggle line numbers 
   1 class NoBlueProxy( Proxy ):
   2     def Blue( self ):
   3         return 0

使用： >>> rgb = RGB( 100, 192, 240 )

>>> rgb.Red()

100

>>> proxy = Proxy( rgb )

>>> proxy.Green()

192

>>> noblue = NoBlueProxy( rgb )

>>> noblue.Green()

192

>>> noblue.Blue()

0

}}} 使用： >>> rgb = RGB( 100, 192, 240 )

>>> rgb.Red()

100

>>> proxy = Proxy( rgb )

>>> proxy.Green()

192

>>> noblue = NoBlueProxy( rgb )

>>> noblue.Green()

192

>>> noblue.Blue()

0

designpattern (last edited 2009-12-25 07:10:09 by localhost)