的Lua /科羅娜SDK錯誤

Question

我在這個問題上，我不能找到一個解決方案：

「level1.lua：161試圖指數全球‘箱子’（一個零值）」

它發生時，它應該改變線161板條箱的位置，但是「的centerX +（的centerX * event.xGravity」不回零，導致「文字信息」顯示正確的值。

代碼如下

----------------------------------------------------------------------------------------- 
    -- 
    -- level1.lua 
    -- 
    ----------------------------------------------------------------------------------------- 

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

    -- include Corona's "physics" library 
    local physics = require "physics" 
    physics.start(); physics.pause() 

    -------------------------------------------- 
    -- Sounds 
    local shakeSound = audio.loadSound ("shake.mp3") 

    -- Display, metrics stuff 
    local centerX = display.contentWidth/2 
    local centerY = display.contentHeight/2 

    -- forward declarations and other locals 
    local screenW, screenH, halfW = display.contentWidth, display.contentHeight, display.contentWidth*0.5 

    ----------------------------------------------------------------------------------------- 
    -- BEGINNING OF YOUR IMPLEMENTATION 
    -- 
    -- NOTE: Code outside of listener functions (below) will only be executed once, 
    --  unless storyboard.removeScene() is called. 
    -- 
    ----------------------------------------------------------------------------------------- 


    -- Text parameters 
    local labelx = 50 
    local x = 220 
    local y = 95 
    local fontSize = 24 

    local frameUpdate = false     -- used to update our Text Color (once per frame) 

    local xglabel = display.newText("gravity x = ", labelx, y, native.systemFont, fontSize) 
    xglabel:setTextColor(255,255,255) 




    local textMessage = function(str, location, scrTime, size, color, font) 

     local x, t 

     size = tonumber(size) or 24 
     color = color or {255, 255, 255} 
     font = font or "Helvetica" 

     -- Determine where to position the text on the screen 
     if "string" == type(location) then 
      if "Top" == location then 
       x = display.contentHeight/4 
      elseif "Bottom" == location then 
       x = (display.contentHeight/4)*3 
      else 
       -- Assume middle location 
       x = display.contentHeight/2 
      end 
     else 
      -- Assume it's a number -- default to Middle if not 
      x = tonumber(location) or display.contentHeight/2 
     end 

     scrTime = (tonumber(scrTime) or 3) * 1000  -- default to 3 seconds (3000) if no time given 

     t = display.newText(str, 0, 0, font, size) 
     t.x = display.contentWidth/2 
     t.y = x 
     t:setTextColor(color[1], color[2], color[3]) 

     -- Time of 0 = keeps on screen forever (unless removed by calling routine) 
     -- 
     if scrTime ~= 0 then 

      -- Function called after screen delay to fade out and remove text message object 
      local textMsgTimerEnd = function() 
       transition.to(t, {time = 500, alpha = 0}, 
        function() t.removeSelf() end) 
      end 

      -- Keep the message on the screen for the specified time delay 
      timer.performWithDelay(scrTime, textMsgTimerEnd) 
     end 

     return t  -- return our text object in case it's needed 

    end -- textMessage() 




    -- Called when the scene's view does not exist: 
    function scene:createScene(event) 
     local group = self.view 

     -- create a grey rectangle as the backdrop 
     local background = display.newRect(0, 0, screenW, screenH) 
     background:setFillColor(128) 

     -- make a crate (off-screen), position it, and rotate slightly 
     local crate = display.newImage('crate.png') --display.newImageRect("crate.png", 90, 90) 
     crate.x = centerX 
     crate.y = centerY 
     crate.rotation = 15 

     -- add physics to the crate 
     physics.addBody(crate, { density=1.0, friction=0.3, bounce=0.3 }) 

     -- create a grass object and add physics (with custom shape) 
     local grass = display.newImageRect("grass.png", screenW, 82) 
     grass:setReferencePoint(display.BottomLeftReferencePoint) 
     grass.x, grass.y = 0, display.contentHeight 

     -- define a shape that's slightly shorter than image bounds (set draw mode to "hybrid" or "debug" to see) 
     local grassShape = { -halfW,-34, halfW,-34, halfW,34, -halfW,34 } 
     physics.addBody(grass, "static", { friction=0.3, shape=grassShape }) 

     -- all display objects must be inserted into group 
     group:insert(background) 
     group:insert(grass) 
     group:insert(crate) 
    end 

    -- Called immediately after scene has moved onscreen: 
    function scene:enterScene(event) 
     local group = self.view 

     physics.start() 

    end 

    -- Called when scene is about to move offscreen: 
    function scene:exitScene(event) 
     local group = self.view 

     physics.stop() 

    end 

    -- If scene's view is removed, scene:destroyScene() will be called just prior to: 
    function scene:destroyScene(event) 
     local group = self.view 

     package.loaded[physics] = nil 
     physics = nil 
    end 

    -- Accelerometer 
    local function onAccelerate(event) 


     -- Move our object based on the accelerator values -- 
     textMessage(tostring(centerX + (centerX * event.xGravity)), "naosei", 0.5, 12, {255, 255, 0}) 
     crate.x = centerX + (centerX * event.xGravity) 
     crate.y = centerY + (centerY * event.yGravity * -1) 

     -- sound beep if Shake'n 
     if event.isShake == true then 
     textMessage("Shake!", "Top", 3, 52, {255, 255, 0}) 
      audio.play(shakeSound) 
     end 
    end 

    ----------------------------------------------------------------------------------------- 
    -- END OF YOUR IMPLEMENTATION 
    ----------------------------------------------------------------------------------------- 
    -- Add runtime listeners 
    Runtime:addEventListener ("accelerometer", onAccelerate); 

    -- Add scene listeners 
    -- "createScene" event is dispatched if scene's view does not exist 
    scene:addEventListener("createScene", scene) 

    -- "enterScene" event is dispatched whenever scene transition has finished 
    scene:addEventListener("enterScene", scene) 

    -- "exitScene" event is dispatched whenever before next scene's transition begins 
    scene:addEventListener("exitScene", scene) 

    -- "destroyScene" event is dispatched before view is unloaded, which can be 
    -- automatically unloaded in low memory situations, or explicitly via a call to 
    -- storyboard.purgeScene() or storyboard.removeScene(). 
    scene:addEventListener("destroyScene", scene) 

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

    return scene 

Answer 1

「level1.lua：161試圖指數全球‘箱子’（一個零值）」

因爲沒有crate可變範圍上線161

你確實有一個名爲crate變量在createScene之內，但它的本地，所以它只在該函數內可見。第161行是一個不同的函數（onAccelerate），那裏沒有本地的crate變量，所以Lua查找全局（_G['crate']），取回nil，並嘗試對其進行索引。因此錯誤。

最簡單的修復方法：從第108行的crate中刪除關鍵字local，以便創建全局。這並不漂亮，但它應該起作用。

Answer 2

我會避免使用全局變量，因爲內存泄漏問題。 我所做的是在根作用域中定義顯示對象名稱，然後在createScene函數中設置它們。我認爲這有助於lua做垃圾回收。

local background, crate 

function scene:createScene(event) 
    local group = self.view 
    local background = display.newRect(0, 0, screenW, screenH) 
    local crate = display.newImage('crate.png') 
    group:insert(background) 
    group:insert(crate) 
end