状态模式（State Pattern）
意图：允许对象在内部状态发生改变时改变它的行为，对象看起来好像修改了它的类。
主要解决：对象的行为依赖于它的状态（属性），并且可以根据它的状态改变而改变它的相关行为。
何时使用：代码中包含大量与对象状态有关的条件语句。
如何解决：将各种具体的状态类抽象出来。
python
from abc import ABCMeta, abstractmethod
class Context(metaclass=ABCMeta):
""" 状态模式的上下文环境 """
def __init__(self):
self.__states = []
self.__cur_state = None
# 状态发生变化的依赖属性，当这一变量由多个变量共同决定时可以将其定义成一个类
self.state_info = 0
def add_state(self, state):
""" 添加状态 """
if state not in self.__states:
self.__states.append(state)
def change_state(self, state):
""" 改变状态 """
if state is None:
return False
if self.__cur_state is None:
print("初始化为：", state.get_name())
else:
print("由", self.__cur_state.get_name(), "变为", state.get_name())
self.__cur_state = state
self.add_state(state)
return True
def get_state(self):
""" 获取状态 """
return self.__cur_state
def _set_state_info(self, state_info):
self.__state_info = state_info
for state in self.__states:
if state.is_match(state_info):
self.change_state(state)
def _get_state_info(self):
return self.__state_info
class State:
""" 状态基类(负责状态的定义和接口的统一) """
def __init__(self, name):
self.__name = name
def get_name(self):
return self.__name
def is_match(self, state_info):
""" 状态的属性state_info是否在当前状态的范围"""
return False
@abstractmethod
def behavior(self, context):
pass
class Water(Context):
""" 水(H2O)"""
def __init__(self):
super().__init__()
self.add_state(SolidState("固态"))
self.add_state(LiquidState("液态"))
self.add_state(GaseousState("气态"))
self.set_temperature(25)
def get_temperature(self):
""" 获取温度 """
return self._get_state_info()
def set_temperature(self, temperature):
""" 设置温度 """
self._set_state_info(temperature)
def rise_temperature(self, step):
""" 温度上升 """
self.set_temperature(self.get_temperature() + step)
def reduce_temperature(self, step):
""" 温度下降 """
self.set_temperature(self.get_temperature() - step)
def behavior(self):
""" 不同的行为状态 """
state = self.get_state()
if isinstance(state, State):
state.behavior(self)
# 单例装饰器
def singleton(cls, *args, **kwargs):
""" 构造一个单例装饰器 """
instance = {}
def __singleton(*args, **kwargs):
if cls not in instance:
instance[cls] = cls(*args, **kwargs)
return instance[cls]
return __singleton
@singleton
class SolidState(State):
""" 固态状态 """
def __init__(self, name):
super().__init__(name)
def is_match(self, state_info):
return state_info < 0
def behavior(self, context):
print("我是固态，当前温度：" + str(context._get_state_info()) + "℃")
@singleton
class LiquidState(State):
""" 液态状态 """
def __init__(self, name):
super().__init__(name)
def is_match(self, state_info):
return state_info >= 0 and state_info < 100
def behavior(self, context):
print("我是液态，当前温度：" + str(context._get_state_info()) + "℃")
@singleton
class GaseousState(State):
""" 气态状态 """
def __init__(self, name):
super().__init__(name)
def is_match(self, state_info):
return state_info >= 100
def behavior(self, context):
print("我是气态，当前温度：" + str(context._get_state_info()) + "℃")
if __name__ == '__main__':
water = Water()
water.behavior()
water.set_temperature(-4)
water.behavior()
water.rise_temperature(18)
water.behavior()
water.rise_temperature(110)
water.behavior()
dart 实现
main(List<String> args) {
Context context = Context();
StartState startState = StartState();
startState.doAction(context);
print(context.state);
StopState stopState = new StopState();
stopState.doAction(context);
print(context.state);
}
//////////////////////////////////////////////////////////////////
///
/// 创建一个接口
///
abstract class State {
void doAction(Context context);
}
///
/// 创建 Context 类
///
class Context {
State? state = null;
Context();
}
///
/// 创建实现接口的实体类
///
class StartState implements State {
void doAction(Context context) {
print("Player is in start state");
context.state = this;
}
@override
String toString() {
return "Start State";
}
}
class StopState implements State {
void doAction(Context context) {
print("Player is in stop state");
context.state = this;
}
@override
String toString() {
return "Stop State";
}
}
