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<h1 id="python设计模式之观察者模式"><a href="http://dongweiming.github.io/python-observer.html"Permalink to python设计模式之观察者模式"" target="_blank">python设计模式之观察者模式</a></h1><h2 id="观察者模式">观察者模式</h2><p>当我们希望一个对象的状态发生变化，那么依赖与它的所有对象都能相应变化(获得通知),那么就可以用到Observer模式，
其中的这些依赖对象就是观察者的对象，那个要发生变化的对象就是所谓'观察者'</p><h2 id="python的例子">python的例子</h2><pre><code># 这个是观察者基类
class Subject(object):
def __init__(self):
self._observers = []
# 添加依赖的对象
def attach(self, observer):
if not observer in self._observers:
self._observers.append(observer)
# 取消添加
def detach(self, observer):
try:
self._observers.remove(observer)
except ValueError:
pass
# 这里只是通知上面注册的依赖对象新的变化
def notify(self, modifier=None):
for observer in self._observers:
# 可以设置过滤条件，对不符合过滤条件的更新
if modifier != observer:
observer.update(self)
# 观察者类
class Data(Subject):
def __init__(self, name=''):
super(Data, self).__init__()
self.name = name
self._data = 0
# python2.6新增的写法,获取属性为property，设置属性为(假设属性名字为x)@x.setter,删除为@x.deleter
@property
def data(self):
return self._data
@data.setter
def data(self, value):
self._data = value
self.notify()
# 这里有2个被观察者，也就是依赖的对象，每次Data有改变，这2个view都会变动
class HexViewer(object):
def update(self, subject):
print 'HexViewer: Subject %s has data 0x%x' % (subject.name, subject.data)
class DecimalViewer(object):
def update(self, subject):
print 'DecimalViewer: Subject %s has data %d' % (subject.name, subject.data)
if __name__ == '__main__':
data1 = Data('Data 1')
data2 = Data('Data 2')
view1 = DecimalViewer()
view2 = HexViewer()
data1.attach(view1)
data1.attach(view2)
data2.attach(view2)
data2.attach(view1)
print "Setting Data 1 = 10"
data1.data = 10
print "Setting Data 2 = 15"
data2.data = 15
print "Setting Data 1 = 3"
data1.data = 3
print "Setting Data 2 = 5"
data2.data = 5
print "Update data1's view2 Because view1 is be filtered"
data1.notify(modifier=view1)
print "Detach HexViewer from data1 and data2."
data1.detach(view2)
data2.detach(view2)
print "Setting Data 1 = 10"
data1.data = 10
print "Setting Data 2 = 15"
data2.data = 15</code></pre>
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