lua實作的 FSM(finite-state machine)

代碼實作

為方便閱讀，只粘了核心代碼，完整版可移步Github：Lua_FSM - SouthBegonia

狀態基類 BaseFSMState.lua

---@class BaseFSMState FSM狀態基類
---@field public stateName string @狀態名
---@field private entryCondition function @進入此狀態的條件
BaseFSMState = {}

BaseFSMState.__index = BaseFSMState;

---實體化狀態
---@public
---@param stateName string
function BaseFSMState.New(stateName)
    ---@type BaseFSMState
    local fsmState = setmetatable({}, BaseFSMState);

    fsmState.stateName = stateName;
    fsmState.entryCondition = nil;

    return fsmState;
end

---設定 進入此狀態的條件
---@public
---@param condition function
function BaseFSMState:SetEntryCondition(condition)
    self.entryCondition = condition;
end

---判斷 是否滿足進入此狀態的條件
---@public
---@return boolean
function BaseFSMState:CheckEntryCondition()
    if (self.entryCondition ~= nil) then
        return self.entryCondition();
    end

    return true;
end

---進入狀態
---@public
function BaseFSMState:OnEnter()
end

---更新狀態
---@public
function BaseFSMState:OnUpdate()
end

---離開狀態
---@public
function BaseFSMState:OnLeave()
end

狀態機基類 BaseFSM.lua

---@class BaseFSM FSM基類
---@field private states table<string, BaseFSMState> @持有的狀態 的表（key=BaseFSM.stateName  value=https://www.cnblogs.com/SouthBegonia/archive/2022/11/19/BaseFSMState）
---@field private previousState BaseFSMState @先前狀態
---@field private currentState BaseFSMState @當前狀態
BaseFSM = {};

BaseFSM.__index = BaseFSM;

---構造 狀態機實體
---@public
---@return BaseFSM
function BaseFSM.New()
    ---@type BaseFSM
    local fsm = setmetatable({}, BaseFSM);

    fsm.states = {};
    fsm.previousState = nil;
    fsm.currentState = nil;

    return fsm;
end

---添加 狀態
---@param fsmState BaseFSMState
---@return boolean @是否 成功添加狀態
function BaseFSM:AddState(fsmState)
    if (fsmState == nil) then
        --Error
        return false;
    end

    if (self.states[fsmState.stateName] ~= nil) then
        --Error
        return false;
    end

    self.states[fsmState.stateName] = fsmState;
    return true;
end

---設定 初始狀態
---@param fsmStateName string
function BaseFSM:SetStartState(fsmStateName)
    local startFSMState = self.states[fsmStateName];
    if (startFSMState == nil) then
        --Error
        return false;
    end

    self.previousState = nil;
    self.currentState = startFSMState;
    self.currentState:OnEnter();

    return true;
end

---獲取 當前狀態
---@public
---@return BaseFSMState
function BaseFSM:GetCurrentState()
    return self.currentState;
end

---切換到 目標狀態
---@public
---@param fsmStateName string
---@return boolean
function BaseFSM:ChangeState(fsmStateName)
    ---@type BaseFSMState
    local targetFSMState = self.states[fsmStateName];
    if (targetFSMState == nil) then
        --Error
        return false;
    end

    if (self.currentState == targetFSMState) then
        --Error
        return false;
    end

    if (not targetFSMState:CheckEntryCondition()) then
        --Log
        return false;
    end

    self.currentState:OnLeave();

    self.previousState = self.currentState;
    self.currentState = targetFSMState;

    self.currentState:OnEnter();

    return true;
end

---@public
function BaseFSM:Update()
    if (self.currentState ~= nil) then
        self.currentState:OnUpdate();
    end
end

測驗：

---------- 添加 場景狀態列舉 ----------
local SceneFSMStateDefine = {
    Login = "Login",
    Home = "Home",
    Battle = "Battle",
}

---------- 實體化 各場景狀態 ----------
---@type BaseFSMState
local sceneLoginFSMState = BaseFSMState.New(SceneFSMStateDefine.Login);
sceneLoginFSMState.OnEnter = function()
    print("進入 Login狀態");
end
sceneLoginFSMState.OnLeave = function()
    print("退出 Login狀態");
end
---@type BaseFSMState
local sceneHomeFSMState = BaseFSMState.New(SceneFSMStateDefine.Home);
sceneHomeFSMState.OnEnter = function()
    print("進入 Home狀態");
end
sceneHomeFSMState.OnLeave = function()
    print("退出 Home狀態");
end
---@type BaseFSMState
local sceneBattleFSMState = BaseFSMState.New(SceneFSMStateDefine.Battle);
sceneBattleFSMState.OnEnter = function()
    print("進入 Battle狀態");
end
sceneBattleFSMState.OnLeave = function()
    print("退出 Battle狀態");
end

---------- 實體化 場景狀態機 ----------
print("---------- 構造 FSM ----------");
local sceneFSM = BaseFSM.New();
sceneFSM:AddState(sceneLoginFSMState);
sceneFSM:AddState(sceneHomeFSMState);
sceneBattleFSMState:SetEntryCondition(function()
    --設定Battle狀態的切換條件:僅當在Home狀態時才可切換至Battle
    return sceneFSM:GetCurrentState() == sceneHomeFSMState;
end)
sceneFSM:AddState(sceneBattleFSMState);

print("---------- 設定 FSM初始狀態為 Login ----------");
sceneFSM:SetStartState(SceneFSMStateDefine.Login);

print("---------- 切換 FSM狀態為 Battle ----------");
sceneFSM:ChangeState(SceneFSMStateDefine.Battle);

print("---------- 切換 FSM狀態為 Home ----------");
sceneFSM:ChangeState(SceneFSMStateDefine.Home);

print("---------- 切換 FSM狀態為 Battle ----------");
sceneFSM:ChangeState(SceneFSMStateDefine.Battle);

--[[
    OUTPUT:
    ---------- 構造 FSM ----------
    ---------- 設定 FSM初始狀態為 Login ----------
    進入 Login狀態
    ---------- 切換 FSM狀態為 Battle ----------
    ---------- 切換 FSM狀態為 Home ----------
    退出 Login狀態
    進入 Home狀態
    ---------- 切換 FSM狀態為 Battle ----------
    退出 Home狀態
    進入 Battle狀態
--]]

參考文章

• 有限狀態機 - 魂淡1994
• 在Lua中實作面向物件特性——模擬類、繼承、多型 - 馬三小伙兒
• FSMKit - QFramework
• Fsm - GameFramework
• Lua中使用狀態機FSM簡單例子 - Kevin_綠豆芽

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