試圖指數全球「前」（一個零值）

Question

我編碼在Lua與科羅娜SDK和我在得到這個錯誤「試圖指數全球‘前’（一個零值）」 75號線

我在game.lua中執行此操作，從main.lua重定向（此部分工作正常） ....鏈接是pastebin，因爲stackoverflow混淆了代碼！

--requires 
local storyboard = require "storyboard" 
local scene = storyboard.newScene() 

local physics = require "physics" 
physics.start() 


function scene:createScene(event) 
    local screenGroup = self.view 

    local bkg = display.newImage("bkg.png") 

    local back = display.newImage("back.png") 
    back.y=450 
    back.speed = 1 
    back:setReferencePoint(display.BottomLeftReferencePoint) 

    local back1 = display.newImage("back.png") 
    back1.y=450 
    back1.x=2400 
    back1.speed = 1 
    back1:setReferencePoint(display.BottomLeftReferencePoint) 

    local front = display.newImage("front1.png") 
    front.y=470 
    front.speed = 4 
    front:setReferencePoint(display.BottomLeftReferencePoint) 

    local front1 = display.newImage("front1.png") 
    front1.y=470 
    front1.x=2400 
    front1.speed = 4 
    front1:setReferencePoint(display.BottomLeftReferencePoint) 

    local bird = display.newImage("bird.png") 
    bird.y = 285; bird.x= 200 
    physics.addBody(bird, "dynamic", 
        {density=0.1, bounce=0.1, friction=0.2, radius=10}) 
end 

function scrollHill(self,event) 
    if self.x < -1800 then 
     self.x = 1400 - self.speed * 2 
    else 
     self.x = self.x - self.speed 
    end 
end 

function activateBird(self,event) 
    self:applyForce(0, -1.5, self.x, self.y) 
end 

function touchScreen(event) 
    print("touch_ok") 
    if event.phase =="began" then 
    bird.enterFrame = activateBird 
    Runtime:addEventListener("enterFrame", bird) 
    end 

    if event.phase =="ended" then 
    Runtime:removeEventListener("enterFrame", bird) 
    end 
end 


function scene:enterScene(event) 
    Runtime:addEventListener("touch", touchScreen) 

    front.enterFrame = scrollHill 
    Runtime:addEventListener("enterFrame", front) 

    front1.enterFrame = scrollHill 
    Runtime:addEventListener("enterFrame", front1) 

    back.enterFrame = scrollHill 
    Runtime:addEventListener("enterFrame", back) 

    back1.enterFrame = scrollHill 
    Runtime:addEventListener("enterFrame", back1) 
end 

function scene:exitScene(event) 
end 

function scene:destroyScene(event) 
end 

scene:addEventListener("createScene", scene) 
scene:addEventListener("enterScene", scene) 
scene:addEventListener("exitScene", scene) 
scene:addEventListener("destroyScene", scene) 

return scene 

Answer 1

很可能這是因爲變量未能初始化。

local front = display.newImage("front1.png") 

確保圖像文件位於同一目錄game.lua，並且文件名拼寫正確。

Answer 2

您需要在模塊範圍內爲createScene()添加forward declarations，以便它們可用於enterScene()。另外，當你使用destroyScene時，一定要刪除你所有的聽衆。

例：

-- Use a forward declaration here so `front` 
-- is in the module's scope 
local front 

function scene:createScene(event) 
    -- ... 
    -- Don't use `local` here because `front` was defined 
    -- above. 
    front = display.newImage("front1.png") 
    front.y=470 
    front.speed = 4 
    front:setReferencePoint(display.BottomLeftReferencePoint) 
    -- ... 
end 

function scene:enterScene(event) 
    -- ... 
    -- Since `front` is in the parent's scope, 
    -- we can access it here 
    Runtime:addEventListener("enterFrame", front) 
    -- ... 
end 

function scene:destroyScene(event) 
    -- Be sure to remove your listeners here 
    Runtime:removeEventListener("enterFrame", front) 
end