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(搬運工)基于Lua的State Pattern

Posted on 2012-05-07 13:58 點點滴滴閱讀(438) 評論(0) 編輯收藏引用

class.lua實現了在Lua中創建類的模擬，非常方便。class.lua參考自http://lua-users.org/wiki/SimpleLuaClasses

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-- class.lua 

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-- Compatible with Lua 5.1 (not 5.0). 

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function class(base, init) 

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local c = {} -- a new class instance 

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if not init and type(base) == 'function' then

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init = base 

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base = nil

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elseif type(base) == 'table' then

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-- our new class is a shallow copy of the base class! 

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for i,v in pairs(base) do

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c[i] = v 

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end

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c._base = base 

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end

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-- the class will be the metatable for all its objects, 

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-- and they will look up their methods in it. 

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c.__index = c 

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-- expose a constructor which can be called by <classname>(<args>) 

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local mt = {} 

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mt.__call = function(class_tbl, ...) 

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local obj = {} 

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setmetatable(obj,c) 

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-- below 2 lines are updated based on the Comments from 'http://lua-users.org/wiki/SimpleLuaClasses' 

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-- if init then 

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-- init(obj,...) 

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if class_tbl.init then

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class_tbl.init(obj,...) 

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else

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-- make sure that any stuff from the base class is initialized! 

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if base and base.init then

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base.init(obj, ...) 

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end

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end

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return obj 

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end

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c.init = init 

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c.is_a = function(self, klass) 

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local m = getmetatable(self) 

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while m do

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if m == klass then return true end

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m = m._base 

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end

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return false 

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end

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setmetatable(c, mt) 

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return c 

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end

State基類，包含三個stub函數，enter()和exit()分別在進入和退出state時被執行，onUpdate()函數將會在state被激活時的每幀被執行。

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require "class"

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State = class() 

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function State:init( name ) 

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self.name = name 

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end

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function State:enter() 

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end

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function State:onUpdate() 

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end

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function State:exit() 

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end

StateMachine類，該類集成了Moai的MOAIThread類。MOAIThread類似于Lua中的coroutine，但是在Moai中被yield的MOAIThread，會在game loop的每幀中被自動resume，見StateMachine:updateState函數，利用此特點，來實現每幀執行State:onUpdate函數。

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require "State"

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StateMachine = class() 

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function StateMachine:init() 

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self.currentState = nil

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self.lastState = nil

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end

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function StateMachine:run() 

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if ( self.mainThread == nil ) 

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then

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self.mainThread = MOAIThread.new() 

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self.mainThread:run( self.updateState, self ) 

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end

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end

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function StateMachine:stop() 

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if ( self.mainThread ) 

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then

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self.mainThread:stop() 

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end

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end

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function StateMachine:setCurrentState( state ) 

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if ( state and state:is_a( State ) ) 

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then

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if ( state == self.currentState ) 

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then

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print( "WARNING @ StateMachine::setCurrentState - " .. 

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"var state [" .. state.name .. "] is the same as current state" ) 

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return

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end

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self.lastState = self.currentState 

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self.currentState = state 

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if ( self.lastState ) 

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then

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print( "exiting state [" .. self.lastState.name .. "]" ) 

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self.lastState:exit() 

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end

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print( "entering state [" .. self.currentState.name .. "]" ) 

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self.currentState:enter() 

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else

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print( "ERROR @ StateMachine::setCurrentState - " .. 

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"var [state] is not a class type of State" ) 

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end

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end

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function StateMachine:updateState() 

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while ( true ) 

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do

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if ( self.currentState ~= nil ) 

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then

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self.currentState:onUpdate() 

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end

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coroutine.yield() 

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end

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end

如何利用State和StateMachine類的示例，首先定義兩個state。
SampleState.lua

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require "State"

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State1 = class( State ) 

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function State1:init() 

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State.init( self, "State1" ) 

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end

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function State1:enter() 

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self.i = 0 

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end

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function State1:exit() 

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self.i = 0 

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end

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function State1:onUpdate() 

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print( self.name .. " is updated" ) 

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self.i = self.i + 1 

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print( "self.i=" .. self.i ) 

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if ( self.i == 10 ) 

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then

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print( state2 ) 

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SM:setCurrentState( state2 ) 

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self.i = 0 

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end

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end

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----------------------- 

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State2 = class( State ) 

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function State2:init() 

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State.init( self, "State2" ) 

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end

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function State2:onUpdate() 

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print( "State2 is updated" ) 

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end

test.lua

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require "StateMachine"

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require "SampleState"

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SM = StateMachine() 

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SM:run() 

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state1 = State1() 

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state2 = State2() 

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SM:setCurrentState( state1 )

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