尝试索引本地"def"(nil值)

问题描述

我正在开发游戏.在某个时候，我想创建特殊的GameObject.特殊的GameObject称为Projectile，与GameObject相同，但具有dx和dy以及只有射弹才具有的其他一些功能.我试图使Projectile扩展GameObject类，但是在尝试创建Projectile实例时遇到问题.我尝试了不同的方式来声明Projectile和改组声明顺序，但是似乎无法弄清楚为什么我得到标题中提到的错误.谢谢！

I'm working on a game. At a certain point, I would like to create special GameObject. The special GameObject is called Projectile and is the same as GameObject but has a dx and dy as well as some other functions that only a projectile will have. I am trying to make Projectile extend the GameObject class, but I run into issues when I try to create an instance of Projectile. I've tried different ways of declaring Projectile and shuffling declaration order but can't seem to figure out why I'm getting the error mentioned in the title. Thank you!

以下工作正常:

table.insert(self.dungeon.currentRoom.objects, GameObject(
                        GAME_OBJECT_DEFS['pot'],
                        self.player.x,
                        self.player.y
                    ))

但是当我将"GameObject"更改为"Projectile"时，不会.

But when I change "GameObject" to "Projectile" it does not.

table.insert(self.dungeon.currentRoom.objects, Projectile(
                        GAME_OBJECT_DEFS['pot'],
                        self.player.x,
                        self.player.y
                    ))

其余为支持代码.我正在使用Matthias Richter的课程代码

The rest is supporting code. I'm using Class code from Matthias Richter

require 'src/Projectile'
require 'src/GameObject'
require 'src/game_objects'

GameObject = Class{}

function GameObject:init(def, x, y)
    -- string identifying this object type
    self.type = def.type

    self.texture = def.texture
    self.frame = def.frame or 1

    -- whether it acts as an obstacle or not
    self.solid = def.solid

    self.defaultState = def.defaultState
    self.state = self.defaultState
    self.states = def.states

    -- dimensions
    self.x = x
    self.y = y
    self.width = def.width
    self.height = def.height

    -- default empty collision callback
    self.onCollide = def.onCollide
end

Projectile = Class{__includes = GameObject}

function Projectile:init()
    GameObject.init(self, def)

    self.dx = 0
    self.dy = 0
end

GAME_OBJECT_DEFS = {
    ['pot'] = {
        type = 'pot',
        texture = 'tiles',
        frame = 14,
        width = 16,
        height = 16,
        solid = true,
        defaultState = 'idle',
        states = {
            ['idle'] = {
                frame = 14,
            }
        },
        onCollide = function()
        end
    }
}

推荐答案

function Projectile:init()
    GameObject.init(self, def)

    self.dx = 0
    self.dy = 0
end

def 为 nil

如此

function GameObject:init(def, x, y)
    -- string identifying this object type
    self.type = def.type

您为nil值编制索引.

you index a nil value.

x 和 y

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