狀態(tài)模式的使用必然會增加系統(tǒng)類和對象的個數(shù)。
狀態(tài)模式的結(jié)構(gòu)與實現(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 “開閉原則” 并不太好，對于可以切換狀態(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，否則無法切換到新增狀態(tài)，而且修改某個狀態(tài)類的行為也需修改對應(yīng)類的源代碼。

應(yīng)用場景

行為隨狀態(tài)改變而改變的場景。
條件、分支語句的代替者。

代碼示例

在這里插入圖片描述

這是一個狀態(tài)圖，具有 “有 25 分錢”、“沒有 25 分錢”、“售出糖果”、“糖果售罄” 這 4 個狀態(tài)。同時也對應(yīng) 4 個動作：“投入 25 分錢”，“退回 25 分錢”，“轉(zhuǎn)動曲柄” 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)建實例變量來持有當(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__":
    # 以下是代碼測試
    gumball_machine = GumballMachine(5) # 裝入5 個糖果
    print(gumball_machine)
    gumball_machine.insert_quarter() # 投入25分錢
    gumball_machine.turn_crank() # 轉(zhuǎn)動曲柄
    print(gumball_machine)
    gumball_machine.insert_quarter() #投入25分錢
    gumball_machine.eject_quarter()  # 退錢
    gumball_machine.turn_crank()     # 轉(zhuǎn)動曲柄
    print(gumball_machine)
    gumball_machine.insert_quarter() # 投入25分錢
    gumball_machine.turn_crank() # 轉(zhuǎn)動曲柄 
    gumball_machine.insert_quarter() # 投入25分錢 
    gumball_machine.turn_crank()  # 轉(zhuǎn)動曲柄
    gumball_machine.eject_quarter() # 退錢
    print(gumball_machine)