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我在 AS3 中制作了一个游戏，我有 2 个文件。一种是 HWMain 和 HWGame。当我单击开始按钮时，脚本从 HWMain 切换到 HWGame，但出现此错误。

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at HWGame()
at MethodInfo-26()
at MethodInfo-25()

这是我的代码。

public class HWGame extends MovieClip
{
    var INIT_STATE:String = "INIT_STATE";
    var READY_STATE:String = "READY_STATE";
    var PLAYER_STATE:String = "PLAYER_STATE";
    var PLAY_STATE:String = "PLAY_STATE";
    var END_STATE:String = "END_STATE";
    var gameState:String;

    //And another variable

    public function HWGame()
    {
        gameState = INIT_STATE;
        trace(gameState);
        stage.addEventListener(Event.ENTER_FRAME, gameLoop);

        function gameLoop(e:Event):void
        {
            switch (gameState)
            {
                case INIT_STATE :
                    initGame();
                    break;
                case READY_STATE :
                    ready();
                    break;
                case PLAYER_STATE :
                    startPlayer();
                    break;
                case PLAY_STATE :
                    playGame();
                    break;
                case END_STATE :
                    endGame();
                    break;
            }
        }

        function initGame():void
        {
            //I write the long code
        }

        function ready():void
        {
            //I write the long code
        }

        function startPlayer():void
        {
            //I write the long code
        }

        function playGame():void
        {
            //I write the long code
        }

        function endGame():void
        {
            //I write the long code
        }
    }
}

我尝试修复它，我认为错误出现在 gameState = INIT_STATE。我该怎么办？

谢谢。

4

1 回答 1

0

从您引用的内容来看，您的HWGame实例可能尚未添加到显示列表中；因此，stage当null您致电时：

stage.addEventListener(Event.ENTER_FRAME, gameLoop);

在访问之前stage，您可以等到添加到阶段：

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

    public class HWGame extends MovieClip
    {

        var INIT_STATE:String = "INIT_STATE";
        var READY_STATE:String = "READY_STATE";
        var PLAYER_STATE:String = "PLAYER_STATE";
        var PLAY_STATE:String = "PLAY_STATE";
        var END_STATE:String = "END_STATE";
        var gameState:String;

        public function HWGame()
        {
            gameState = INIT_STATE;

            addEventListener(Event.ADDED_TO_STAGE, addedToStageHandler);
        }

        protected function addedToStageHandler(event:Event):void
        {
            removeEventListener(Event.ADDED_TO_STAGE, addedToStageHandler);

            stage.addEventListener(Event.ENTER_FRAME, gameLoop);
        }

        protected function gameLoop(e:Event):void
        {
            switch (gameState)
            {
                case INIT_STATE:
                    initGame();
                    break;
                case READY_STATE:
                    ready();
                    break;
                case PLAYER_STATE:
                    startPlayer();
                    break;
                case PLAY_STATE:
                    playGame();
                    break;
                case END_STATE:
                    endGame();
                    break;
            }
        }

        protected function initGame():void
        {
            //I write the long code
        }

        protected function ready():void
        {
            //I write the long code
        }

        protected function startPlayer():void
        {
            //I write the long code
        }

        protected function playGame():void
        {
            //I write the long code
        }

        protected function endGame():void
        {
            //I write the long code
        }
    }
}
于 2012-07-30T06:43:20.043 回答