Question

我刚开始用Corona弄湿脚，试着和OOP一起工作。这只是一个简单的比赛制作游戏，帮助我像OOP一样思考。我有2个类，一个类将创建一个卡的实例（我将创建这种类型的卡类的多个对象），另一个类是MatchCardsManager类 - 这将创建卡并应用属性

我得到的错误是，在我创建了对象＆＃34; MatchCard＆＃34;我试图应用＆＃34; addEventListener＆＃34;对象。但当我这样做时，我收到以下错误

     Support/Outlaw/Sandbox/5/MatchCardsManager.lua:53: 
attempt to call method 'addEventListener' (a nil value)
        stack traceback:

如果我在addEventListener上注释掉信息，则所有对象都会相应地显示在我在MatchCard Class中创建的构造函数。

以下是我的文件 - 我得到的错误是在MatchCardsManager类

中

mCard[i] = MatchCardsManager:displayPlacementCard(i, temp, x, y)
mCard[i]:addEventListener("touch", myTouch)

任何有关修复此更好或更好方法的帮助或建议将不胜感激。谢谢。

MatchCard类现在只是一个简单的构造函数，因为这不是我的问题

-- MatchCard Class
-- Meta Data
local sceneGroup = sceneGroup

local MatchCard = { }
local MatchCard_mt = { __index = MatchCard } -- metatable

------------------------------------------------
-- PRIVATE FUNCTION 
------------------------------------------------

------------------------------------------------
-- PUBLIC FUNCTION
------------------------------------------------
-- constructor
function MatchCard.new (id, animal, state, imageId, x, y)

    local newMCard = display.newRoundedRect( x, y, 59, 47, 5)
    newMCard.strokeWidth = 3
    newMCard:setFillColor( 0.5 )
    newMCard:setStrokeColor( 1, 0, 0 )
    newMCard.properties = {
        id = id or nil,
        animal = animal or nil,
        state = state or 0, 
        imageId = imageId,
    }

    return setmetatable ( newMCard, MatchCard_mt )

end

MatchCardsManager Class在那里我计划创建许多卡片实例

-- require files
local MatchCard = require('MatchCard') --MatchCard

local sceneGroup = sceneGroup
local MatchCardsManager = {} -- originally we should use a displayGroup

-- TODO: insert group into scene

local animalPicsReference = { "dog", "dog", "cat", "cat", "pig", "pig" , "fish", "fish"} 

-- manager class properties
MatchCardsManager.totalCards = 8
MatchCardsManager.totalPairs = 4
MatchCardsManager.pairsFound = 0
MatchCardsManager.firstCardSelected = 0
MatchCardsManager.secondCardSelected = 0

-- lets create 6 MatchCardFiles
function MatchCardsManager:create()

    local animalPics = animalPicsReference
    local x = 108 - 85
    local y = 125
    print("do we go here never works")

    local mCard = {}

    for i=1, 4  
        do 
           x = x + 85 
           num = math.random(1, #animalPics)
           temp = animalPics[num]
           table.remove(animalPics, num) 
           mCard[i] = MatchCardsManager:displayPlacementCard(i, temp, x, y)
           mCard[i]:addEventListener("touch", myTouch)

    end

    x = 108 - 85
    y = 195 
    for j = 5, 8 do 
            x = x + 85          
           num = math.random(1, #animalPics)
           temp = animalPics[num]
           table.remove(animalPics, num) 
           mCard[j] = MatchCardsManager:displayPlacementCard(j, temp, x, y)
           print(type(mCard[j]))
           mCard[j]:addEventListener("touch", myTouch)
    end
    --mCards:addEventListener("touch", myTouch)
    return mCard
end

local function  myTouch( event )
    if event.phase == "began" then
            print( "You touched the object! "..event.target.imageId)
    end
end

function MatchCardsManager:displayPlacementCard(idx, animal, x, y)
    -- randomly place the cards in the object id

    local card = MatchCard.new(idx, animal, 0, animal, x, y)
    --card:show(x,y) -- displays card and that is it
    print("animal added is "..card.properties.imageId)
    return card
end

return MatchCardsManager

Answer 1

问题出在构造函数中。 local newMCard = display.newRoundedRect(...) 创建一个显示对象，但行： return setmetatable(newMCard, MatchCard_mt) 覆盖display对象所具有的元表，因此它不再能够访问用于查找__index的显示addEventListener元方法。

要解决此问题，您需要了解如何在Lua中添加继承。请参阅Inheritance Tutorial，以便继承addEventListener。解决方案类似于：setmetatable(MatchCard, {__index=ShapeObject})或=display.ShapeObject} ---我无法确定Corona如何实现其类。

得到一个＆＃39; nil＆＃39;将addEventListener方法附加到创建的Object时的值

1 个答案: