LUA and Corona error: Attempt To Call Method ' ' (A Nil Value) - Driving Me Crazy

问题

I would ask your help for an error that is driving me crazy.

Ohh... I'm using LUA with Corona SDK btw...

I am creating an instance of a ship. The ship is being instantiated, I can access its properties, but I can not access any method!! Follow the codes, I do not know what to do:

spaceShip.lua:

require('gameConf')

spaceShip = {}
spaceShip.__index = spaceShip

function spaceShip:New(posX, posY, width, height)
    local _spaceShip = nil
    _spaceShip = {}
    setmetatable(_spaceShip, spaceShip)

    _spaceShip = display.newRect(posX - width/2, posY - height/2, width, height)
    _spaceShip:setFillColor(140, 140, 140, 0)
    _spaceShip.width = width
    _spaceShip.height = height

    local shipShape = { -width/2, -height/2, width/2, -height/2, width/2, height/2, -width/2, height/2 }
    local shipShapeMaterial = { density = 1.0, friction = 1.0, bounce = 0.0 , shape = shipShape}

    local shipMotor = { -width/2, height/3, width/2, height/3, width/2, height/2, -width/2, height/2 }
    local shipMotorMaterial = { density = 1.0, friction = 1.0, bounce = 0.0 , shape = shipMotor}

    physics.addBody( _spaceShip, shipShapeMaterial, shipMotorMaterial )

    return _spaceShip
end

function spaceShip:log()
    print("ship")
end

function spaceShip:applyFrontImpulse()
    local angle = math.rad(self.rotation)
    local xComp, yComp = math.cos(angle), -math.sin(angle)
    local forceMag = 2

    self:applyLinearImpulse(forceMag * xComp, forceMag * yComp, self.x, self.y)
end

and part of main.lua

require('camera')
require('gameConf')
require('meteor')
require('spaceShip')

-- Add Physics
local physics = require( "physics" )
physics.start()
physics.setDrawMode( "hybrid" )
physics.setGravity( 0, 0 )

-- Load camera
local camera = camera:New()

-- Containers
meteorManager = {}
shipManager = {}

-- Load Vector class
vector = require "vector"

-- Create one ship
local myShip = nil;
myShip = {}
myShip = spaceShip:New(600, 200, 30, 60)
table.insert(shipManager, myShip)
camera:insert(myShip)
myShip:log() <----- HERE IS THE ERROR

rest of the code...

The error in terminal is:

2013-03-21 19:18:15.736 Corona Simulator[48347:707] Runtime error: 
2013-03-21 19:18:15.737 Corona Simulator[48347:707] ...t/iOS/Deep Space Harvest/Deep Space Harvest/main.lua:28: attempt to call method 'log' (a nil value)
stack traceback:
[C]: in function 'log'
...t/iOS/Deep Space Harvest/Deep Space Harvest/main.lua:28: in main chunk

回答1:

I suspect the issue is because of this fragment:

_spaceShip = {}
setmetatable(_spaceShip, spaceShip)

_spaceShip = display.newRect(posX - width/2, posY - height/2, width, height)

You set a metatable on _spaceShip, but then assigned a new value to it. At that point the new value you assigned doesn't have the metatable association you established as it's on the value (not variable).

Move setmetatable after _spaceShip = display.newRect....

来源：https://stackoverflow.com/questions/15560813/lua-and-corona-error-attempt-to-call-method-a-nil-value-driving-me-craz

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lua

corona