尝试索引全局变量'city1'（一个空值）

local physics = require"physics" ----
physics.start()
local storyboard = require("storyboard")
local scene = storyboard.newScene()

function scene:enterScene(event)
    city1.enterFrame= scrollCity
    Runtime:addEventListener("enterFrame",city1)

    city2.enterFrame= scrollCity
    Runtime:addEventListener("enterFrame",city2)

    city3.enterFrame= scrollCity
    Runtime:addEventListener("enterFrame",city3)

    city4.enterFrame= scrollCity
    Runtime:addEventListener("enterFrame",city4)

    Runtime:addEventListener("touch",touchScreen)
end

scene:addEventListener("enterScene",scene)
return scene

但是Corona出错了：

game.lua:65: attempt to index globall 'city1' (a nil value)