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Python設(shè)計(jì)模式中的狀態(tài)模式你了解嗎

 更新時(shí)間:2022年02月15日 10:35:43   作者:范桂颶  
這篇文章主要為大家詳細(xì)介紹了Python設(shè)計(jì)模式中的狀態(tài)模式,文中示例代碼介紹的非常詳細(xì),具有一定的參考價(jià)值,感興趣的小伙伴們可以參考一下,希望能夠給你帶來(lái)幫助

狀態(tài)模式

狀態(tài)模式,當(dāng)對(duì)象的內(nèi)部狀態(tài)發(fā)生了改變的時(shí)候,允許對(duì)象執(zhí)行不同的流程。

在這里插入圖片描述

優(yōu)點(diǎn)

  • 封裝了狀態(tài)轉(zhuǎn)換規(guī)則。
  • 枚舉了可能的狀態(tài),在枚舉狀態(tài)之前需要確定狀態(tài)的種類。
  • 將所有與某個(gè)狀態(tài)有關(guān)的行為放到一個(gè)類中,并且可以方便地增加新的狀態(tài),只需要改變對(duì)象狀態(tài)即可改變對(duì)象的行為。
  • 允許狀態(tài)轉(zhuǎn)換邏輯與狀態(tài)對(duì)象合成一體,而不是某一個(gè)巨大的條件語(yǔ)句塊。
  • 可以讓多個(gè)環(huán)境對(duì)象共享一個(gè)狀態(tài)對(duì)象,從而減少系統(tǒng)中對(duì)象的個(gè)數(shù)。

缺點(diǎn)

  • 狀態(tài)模式的使用必然會(huì)增加系統(tǒng)類和對(duì)象的個(gè)數(shù)。
  • 狀態(tài)模式的結(jié)構(gòu)與實(shí)現(xiàn)都較為復(fù)雜,如果使用不當(dāng)將導(dǎo)致程序結(jié)構(gòu)和代碼的混亂。
  • 狀態(tài)模式對(duì) “開閉原則” 并不太好,對(duì)于可以切換狀態(tài)的狀態(tài)模式,增加新的狀態(tài)類需要修改那些負(fù)責(zé)狀態(tài)轉(zhuǎn)換的源代碼,否則無(wú)法切換到新增狀態(tài),而且修改某個(gè)狀態(tài)類的行為也需修改對(duì)應(yīng)類的源代碼。

應(yīng)用場(chǎng)景

  • 行為隨狀態(tài)改變而改變的場(chǎng)景。
  • 條件、分支語(yǔ)句的代替者。

代碼示例

在這里插入圖片描述

這是一個(gè)狀態(tài)圖,具有 “有 25 分錢”、“沒有 25 分錢”、“售出糖果”、“糖果售罄” 這 4 個(gè)狀態(tài)。同時(shí)也對(duì)應(yīng) 4 個(gè)動(dòng)作:“投入 25 分錢”,“退回 25 分錢”,“轉(zhuǎn)動(dòng)曲柄” 和 “發(fā)放糖果”。

class State:
    # 定義state基類
    def insert_quarter(self):
        pass
    def eject_quarter(self):
        pass
    def turn_crank(self):
        pass
    def dispense(self):
        pass

class SoldOutState(State):
    # 繼承State 類
    def __init__(self, gumball_machine):
        self.gumball_machine = gumball_machine
    def __str__(self):
        return "sold_out"
    def insert_quarter(self):
        print("You can't insert a quarter, the machine is sold out")
    def eject_quarter(self):
        print("You can't eject, you haven't inserted a quarter yet")
    def turn_crank(self):
        print("You turned, but ther are no gumballs")
    def dispense(self):
        print("No gumball dispensed")

class SoldState(State):
    # 繼承State 類
    def __init__(self, gumball_machine):
        self.gumball_machine = gumball_machine
    def __str__(self):
        return "sold"
    def insert_quarter(self):
        print("Please wait, we're already giving you a gumball")
    def eject_quarter(self):
        print("Sorry, you already turned the crank")
    def turn_crank(self):
        print("Turning twice doesn't get you another gumball")
    def dispense(self):
        self.gumball_machine.release_ball()
        if gumball_machine.count > 0:
            self.gumball_machine.state = self.gumball_machine.no_quarter_state
        else:
            print("Oops, out of gumballs!")
            self.gumball_machine.state = self.gumball_machine.soldout_state

class NoQuarterState(State):
    # 繼承State 類
    def __init__(self, gumball_machine):
        self.gumball_machine = gumball_machine
    def __str__(self):
        return "no_quarter"
    def insert_quarter(self):
        # 投幣 并且改變狀態(tài)
        print("You inserted a quarter")
        self.gumball_machine.state = self.gumball_machine.has_quarter_state
    def eject_quarter(self):
        print("You haven't insert a quarter")
    def turn_crank(self):
        print("You turned, but there's no quarter")
    def dispense(self):
        print("You need to pay first")

class HasQuarterState(State):
    # 繼承State 類
    def __init__(self, gumball_machine):
        self.gumball_machine = gumball_machine
    def __str__(self):
        return "has_quarter"
    def insert_quarter(self):
        print("You can't insert another quarter")
    def eject_quarter(self):
        print("Quarter returned")
        self.gumball_machine.state = self.gumball_machine.no_quarter_state
    def turn_crank(self):
        print("You turned...")
        self.gumball_machine.state = self.gumball_machine.sold_state
    def dispense(self):
        print("No gumball dispensed")

class GumballMachine:
    def __init__(self, count=0):
        self.count = count
        # 找出所有狀態(tài),并創(chuàng)建實(shí)例變量來(lái)持有當(dāng)前狀態(tài),然后定義狀態(tài)的值
        self.soldout_state = SoldOutState(self)
        self.no_quarter_state = NoQuarterState(self)
        self.has_quarter_state = HasQuarterState(self)
        self.sold_state = SoldState(self)
        if count > 0:
            self.state = self.no_quarter_state
        else:
            self.state = self.soldout_state
    def __str__(self):
        return ">>> Gumball machine current state: %s" % self.state
    def insert_quarter(self):
        # 投入25分錢
        self.state.insert_quarter()
    def eject_quarter(self):
        # 退回25分
        self.state.eject_quarter()
        # print("state", self.state, type(self.state))
    def turn_crank(self):
        # 轉(zhuǎn)動(dòng)曲柄
        # print("state", self.state, type(self.state))
        self.state.turn_crank()
    def release_ball(self):
        # 發(fā)放糖果
        print("A gumball comes rolling out the slot...")
        if self.count > 0:
            self.count -= 1
        
if __name__ == "__main__":
    # 以下是代碼測(cè)試
    gumball_machine = GumballMachine(5) # 裝入5 個(gè)糖果
    print(gumball_machine)
    gumball_machine.insert_quarter() # 投入25分錢
    gumball_machine.turn_crank() # 轉(zhuǎn)動(dòng)曲柄
    print(gumball_machine)
    gumball_machine.insert_quarter() #投入25分錢
    gumball_machine.eject_quarter()  # 退錢
    gumball_machine.turn_crank()     # 轉(zhuǎn)動(dòng)曲柄
    print(gumball_machine)
    gumball_machine.insert_quarter() # 投入25分錢
    gumball_machine.turn_crank() # 轉(zhuǎn)動(dòng)曲柄 
    gumball_machine.insert_quarter() # 投入25分錢 
    gumball_machine.turn_crank()  # 轉(zhuǎn)動(dòng)曲柄
    gumball_machine.eject_quarter() # 退錢
    print(gumball_machine)

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