actionscript-3 - ActionScript 3 : How do I access the properties of the document class?

Question

当我尝试从另一个类访问文档类的一些私有(private)属性时，它会输出以下错误:

1119: Access of possibly undefined property _player through a reference with static type flash.display:Stage.

这是文档类的代码:

    package 
{
    import flash.display.MovieClip;
    import flash.events.Event;
    import flash.events.KeyboardEvent;
    import flash.utils.Timer;
    import flash.events.TimerEvent;
    import flash.ui.Keyboard;
    import collision;
    import player;
    import ground;

    public class engine extends MovieClip
    {
        public var _player:player;
        private var _ground:ground;
        private var _collision:collision;
        private var _right:Boolean;
        private var _space:Boolean;
        private var _left:Boolean;
        private var _touchGround:Boolean;
        private var _jump:Boolean;
        private var _jumpVel:int;
        private var _q:int;
        private var _vx:int;
        private var _vy:int;

        public function engine()
        {
            _player = new player();
            _ground = new ground();
            _collision = new collision();
            addChild(_player);
            addChild(_ground);
            _player.x = stage.stageWidth/2 - _player.width/2;
            _player.y = stage.stageHeight/2 - _player.height/2;
            _ground.x = stage.stageWidth/2 - _ground.width/2;
            _ground.y = stage.stageHeight/2 - _ground.height/2;
            _ground.y += 150;
            _ground.x += 300;
            _q = 0;
            stage.addEventListener(Event.ENTER_FRAME, enterFrame);
            stage.addEventListener(KeyboardEvent.KEY_DOWN,keyDownHandler);
            stage.addEventListener(KeyboardEvent.KEY_UP,keyUpHandler);
        }
        private function enterFrame(e:Event) 
        {
            if(_right)
            {
                if(_vx > 15) 
                {
                    _vx = 15;
                }
                _vx += 2;
            }
            if(_left) 
            {
                if(_vx < -15)
                {
                    _vx = -15;
                }
                _vx -= 2;
            }
            if(_space && _touchGround)
            {
                _jump = true;
            }
            if(_jump)
            {
                _jumpVel = 20 - _q;
                if(_q == 20)
                {
                    _q = 0;
                    _jumpVel = 0;
                    _jump = false;
                }
                else
                {
                    _ground.y += _jumpVel;
                    _q ++;
                }
            }
            _collision.detectCollisions();
            _ground.x -= _vx;
            _ground.y += _vy;
            if(_vx > 0)
            {
                _vx--;
                if(_vx < 0)
                {
                    _vx = 0;
                }
            }
            else if(_vx < 0)
            {
                _vx++;
                if(_vx > 0)
                {
                    _vx = 0;
                }
            }
            if(_vy > 0) 
                {
                    _vy = 0;
                }
            else if(_vy < -10) 
                {
                    _vy = -10;
                }
                trace(_vy);
        }

        private function keyDownHandler(e:KeyboardEvent)
        {
            if(e.keyCode == Keyboard.RIGHT)
            {
                _right = true;
            }
            if(e.keyCode == Keyboard.LEFT) 
            {
                _left = true;
            }
            if(e.keyCode == Keyboard.SPACE)
            {
                _space = true;
            }
        }
        private function keyUpHandler(e:KeyboardEvent)
        {
            if(e.keyCode == Keyboard.RIGHT)
            {
                _right = false;
            }
            if(e.keyCode == Keyboard.LEFT) 
            {
                _left = false;
            }
            if(e.keyCode == Keyboard.SPACE)
            {
                _space = false;
            }

        }
    }
}

这是“碰撞”类的代码。

package
{

    import flash.display.MovieClip;
    import player;
    import engine;

    public class collision extends MovieClip
    {

    private var _playerCol:player = engine._player;


        public function collision()
        {
        }
        public function detectCollisions():void
        {
            _playerCol.y += 7;
        }
    }
}

我正在尝试从碰撞类访问属性“_player”，但出现错误。

Answer 1

目前，您正尝试访问 _player，就好像它是 Engine 类的静态成员一样。您可以将 _player 设为静态，但这会导致代码异味。一种安全的方法是将引用传递给构造函数:

private var _engine:Engine
private var _playerCol:player;
public function collision(engine:Engine){        

   _engine = engine;
   _playerCol = _engine._player
}        

所以在你的 Doc 课上你会有这条线

_collision = new collision(this);

PS。作为提示，类在开始时确实应该有一个大写字母，如果一个变量要公开，请删除下划线，否则将变量保留为私有(private)并为其创建公共(public)属性。此外，您可能需要考虑更改结构，因为它有些笨拙。我建议查看组件实体系统。