AS3 - 在预加载器实现后引用阶段

时间:2014-03-06 19:44:35

标签: actionscript-3 flash flash-builder preloader stage

我刚刚完成了一个小游戏的基本结构,并将简单的预加载器保存到最后。傻我。

经过多次教程后,我发现这个对我有用 - Pre Loader in Flash Builder

预加载器工作,游戏在舞台上,但立即冻结。我的LevelOne代码中对阶段的任何引用都会引发错误。 错误#1009:无法访问空对象引用的属性或方法。

在实现预加载器之前,我的应用程序类(RookiesGame)被用作级别切换器。每个级别都包含在Sprite中。 RookiesGame首先将LevelOne添加到舞台上,然后一旦玩家完成它,RookiesGame将删除LevelOne并将LevelTwo添加到舞台等。

关卡类使用 _stage 变量引用舞台。

由于我一直在学习这个结构,预加载器成为应用程序类,而RookiesGame成为另一个类,这让我很困惑。 _stage var不应该仍然有用吗?将RookiesGame作为关卡切换器可以吗?

无论如何,主要问题是引用Level Classes的阶段。

当前代码:

Preloader Class

工作正常,游戏开始。

package
{
    import flash.display.DisplayObject;
    import flash.display.Shape;
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    import flash.utils.getDefinitionByName;

    [SWF(width="650", height="450", backgroundColor="#FFFFFF", frameRate="60")]

    public class Preloader extends Sprite
    {
        // Private
        private var _preloaderBackground:Shape
        private var _preloaderPercent:Shape;
        private var _checkForCacheFlag:Boolean = true;
        // Constants
        private static const MAIN_CLASS_NAME:String = "RookiesGame";

        public function Preloader()
        {
            trace("Preloader: Initialized.")
            addEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
        }

        public function dispose():void
        {
            trace("Preloader: Disposing.")
            removeEventListener(Event.ENTER_FRAME, onEnterFrame);
            if (_preloaderBackground)
            {
                removeChild(_preloaderBackground);
                _preloaderBackground = null;
            }
            if (_preloaderPercent)
            {
                removeChild(_preloaderPercent);
                _preloaderPercent = null;
            }
        }

        // Private functions

        private function onAddedToStage(e:Event):void
        {
            trace("Preloader: Added to stage.");
            removeEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
            stage.scaleMode = StageScaleMode.SHOW_ALL;
            stage.align = StageAlign.TOP_LEFT;
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }

        private function onEnterFrame(e:Event):void
        {
            if (_checkForCacheFlag == true)
            {
                _checkForCacheFlag = false;
                if (root.loaderInfo.bytesLoaded >= root.loaderInfo.bytesTotal)
                {
                    trace("Preloader: No need to load, all " + root.loaderInfo.bytesTotal + " bytes are cached.");
                    finishedLoading();
                }
                else
                    beginLoading();
            }
            else
            {
                if (root.loaderInfo.bytesLoaded >= root.loaderInfo.bytesTotal)
                {
                    trace("Preloader: Finished loading all " + root.loaderInfo.bytesTotal + " bytes.");
                    finishedLoading();
                }
                else
                {
                    var percent:Number = root.loaderInfo.bytesLoaded / root.loaderInfo.bytesTotal;
                    updateGraphic(percent);
                    trace("Preloader: " + (percent * 100) + " %");
                }
            }
        }

        private function beginLoading():void
        {
            // Might not be called if cached.
            // ------------------------------
            trace("Preloader: Beginning loading.")
            _preloaderBackground = new Shape()
            _preloaderBackground.graphics.beginFill(0x333333)
            _preloaderBackground.graphics.lineStyle(2,0x000000)
            _preloaderBackground.graphics.drawRect(0,0,200,20)
            _preloaderBackground.graphics.endFill()

            _preloaderPercent = new Shape()
            _preloaderPercent.graphics.beginFill(0xFFFFFFF)
            _preloaderPercent.graphics.drawRect(0,0,200,20)
            _preloaderPercent.graphics.endFill()

            addChild(_preloaderBackground)
            addChild(_preloaderPercent)
            _preloaderBackground.x = _preloaderBackground.y = 10
            _preloaderPercent.x = _preloaderPercent.y = 10
            _preloaderPercent.scaleX = 0
        }

        private function updateGraphic(percent:Number):void
        {
            // Might not be called if cached.
            // ------------------------------
            _preloaderPercent.scaleX = percent
        }

        private function finishedLoading():void
        {
            var RookiesGame:Class = getDefinitionByName(MAIN_CLASS_NAME) as Class;

            if (RookiesGame == null)
                throw new Error("Preloader: There is no class \"" + MAIN_CLASS_NAME + "\".");

            var main:DisplayObject = new RookiesGame() as DisplayObject;
            if (main == null)
                throw new Error("Preloader: The class \"" + MAIN_CLASS_NAME + "\" is not a Sprite or MovieClip.");

            addChild(main);
            dispose();
        }
    }
}

RookiesGame Class(曾经是应用程序类)

对舞台的任何引用都会引发#1009错误,当我将stage.addChild更改为 this .addChild

时停止

我还没有使用预加载器进行关卡切换处理程序,所以我不知道stage.focus是如何工作的!

package
{
        import flash.display.MovieClip;
        import flash.display.Sprite;
        import flash.events.Event;

        public class RookiesGame extends Sprite
        {
            private var _levelOne:LevelOne;
            private var _levelTwo:LevelTwo;

                public function RookiesGame()
                {
                _levelOne = new LevelOne(stage);
                _levelTwo = new LevelTwo(stage);
                this.addChild(_levelOne); 
                        this.addEventListener("levelOneComplete",levelTwoSwitchHandler);                        
                }
                private function levelTwoSwitchHandler(event:Event):void
                {
                        this.removeChild(_levelOne);
                    _levelOne = null;
                    this.addChild(_levelTwo);
                        stage.focus = stage;            

                }
            }
}

LevelOne Class

很多#1009错误。任何引用舞台的东西。

类很大,所以我会突出问题块。

引用阶段时添加键盘侦听器时出现#1009错误。

_stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
_stage.addEventListener(KeyboardEvent.KEY_UP, keyUpHandler); 

引用阶段以检查阶段边界时也是#1009。暂时不能将 stage。更改为 this。

private function checkStageBoundaries(gameObject:MovieClip):void
        {
            if (gameObject.x < 50)
            {
                gameObject.x = 50;
            }
            if (gameObject.y < 50)
            {
                gameObject.y = 50;
            }
            if (gameObject.x + gameObject.width > _stage.stageWidth - 50)
            {
                gameObject.x = _stage.stageWidth - gameObject.width - 50;
            }
            if (gameObject.y + gameObject.height > _stage.stageHeight - 50)
            {
                gameObject.y = _stage.stageHeight - gameObject.height - 50;
            }
        }

我稍后在程序中引用_stage来删除事件侦听器。多数民众赞成。

_stage.removeEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
_stage.removeEventListener(KeyboardEvent.KEY_UP, keyUpHandler);  

如何在没有这些错误的情况下引用舞台,并将RookiesGame作为关卡切换器。

LevelOne类结构

显示我如何使用(d)_stage。

package
{
       //import classes

        public class LevelOne extends Sprite
        {
        //Declare the variables to hold the game objects

        //A variable to store the reference to the stage from the application class
        private var _stage:Object;


        public function LevelOne(stage:Object)
            {
                _stage = stage; 
                this.addEventListener(Event.ADDED_TO_STAGE, addedToStageHandler);
            }
            private function addedToStageHandler(event:Event):void
            {
                startGame();
                this.removeEventListener(Event.ADDED_TO_STAGE, addedToStageHandler);
            }
            private function startGame():void
            {
            //Includes _stage references that mess everything up.
            }
            private function levelCleared():void
            {
            //When Level finished, dispatch event to tell RookiesGame to switch levels.
            dispatchEvent(new Event("levelOneComplete", true));
            }
    }         
}

很抱歉,如果那令人困惑,但如果你可以帮我通过LevelOne和RookiesGame课程参考舞台,我将不胜感激。

1 个答案:

答案 0 :(得分:0)

您从stage班级传递空LevelOneRookiesGame。每当您实例化RookiesGame时,构造函数将首先运行,但它尚未添加到显示列表中,因此其对stage的继承引用为null。您需要做的是在ADDED_TO_STAGE类中为RookiesGame添加一个事件监听器:

package
{
    import flash.display.MovieClip;
    import flash.display.Sprite;
    import flash.events.Event;

    public class RookiesGame extends Sprite
    {
        private var _levelOne:LevelOne;
        private var _levelTwo:LevelTwo;

            public function RookiesGame()
            {
                addEventListener( Event.ADDED_TO_STAGE, onAdded );                        
            }
            //added to stage event
            private function onAdded( e:Event ):void {
                removeEventListener( Event.ADDED_TO_STAGE, onAdded );
                _levelOne = new LevelOne(stage);
                _levelTwo = new LevelTwo(stage);
                this.addChild(_levelOne); 
                this.addEventListener("levelOneComplete",levelTwoSwitchHandler);
            }

            ...
        }

此外,如果您使用addChild() LevelOneaddChild(_levelOne)调用stage,它会在_stage添加到显示列表后自己引用ADDED_TO_STAGE,那么您就不会如果要将这些类添加到显示列表中,则需要为这些类创建LevelOne变量。

此外,您在stage中有_stage的监听器,其中{{1}}变量不再为空,因此您可以完全删除类变量{{1}}。