AS3阶段=空？
AS3阶段=空？
提问于 2012-11-19 04:48:40
我刚刚尝试实现一个菜单系统，我在我正在开发的游戏上看到了一个教程，一切都很顺利，直到现在我遇到了阶段设置为null的问题，我不知道如何停止它。不断中断它的行在AvoiderGame.as文件中，它是stage.addEventListener(Event.ADDED_TO_STAGE, init);，它不断返回以下错误
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at AvoiderGame()[M:\Users\Andy\Documents\Programming For Fun\Flash\Tutorial - Avoider Game\Classes\AvoiderGame.as:29]
at States/changeState()[M:\Users\Andy\Documents\Programming For Fun\Flash\Tutorial - Avoider Game\States.as:26]
at mainMenu/brnP_Button()[M:\Users\Andy\Documents\Programming For Fun\Flash\Tutorial - Avoider Game\Classes\mainMenu.as:34]目前，我编写游戏的方式是让它在包含以下代码的States.as中启动。
package
{
import flash.display.*;
import flash.system.fscommand;
public class States extends MovieClip
{
public function States()
{
changeState(null, "menu");
}
public function changeState (currentState, nextState)
{
if (currentState != null)
{
removeChild(currentState);
}
switch(nextState)
{
case "menu": var mm:mainMenu = new mainMenu(changeState);
addChild(mm);
break;
case "game": var g:AvoiderGame = new AvoiderGame(changeState);
addChild(g);
break;
case "exit": fscommand("quit");
break;
}
}
}
}在此之后，它将进入mainMenu.as，直到用户单击play - inside mainMenu.as是以下代码
package
{
import flash.display.*;
import flash.events.*;
public class mainMenu extends MovieClip
{
var theCallBackFunction:Function;
public function mainMenu(callBack)
{
var Background:gameBackground;
Background = new gameBackground();
addChild(Background);
var btnPlay:mmPlay = new mmPlay();
btnPlay.addEventListener(MouseEvent.MOUSE_DOWN, brnP_Button);
btnPlay.x = width/2;
btnPlay.y = height/2 - btnPlay.height/2;
addChild(btnPlay);
var btnExit:mmExit = new mmExit();
btnExit.addEventListener(MouseEvent.MOUSE_DOWN, brnE_Button);
btnExit.x = width/2;
btnExit.y = height/2 - btnExit.height/2;
btnExit.y += btnExit.height + 4;
addChild(btnExit);
theCallBackFunction = callBack;
}
public function brnP_Button(e:MouseEvent)
{
theCallBackFunction(this, "game");
return;
}
public function brnE_Button(e:MouseEvent)
{
theCallBackFunction(this, "exit");
return;
}
}
}这就是它的问题所在-它进入AvoiderGame.as，然后用一个我不知道如何修复的错误返回给我-有人能建议我如何修复它吗？
package
{
import flash.display.MovieClip;
import flash.utils.Timer;
import flash.events.Event;
import flash.events.TimerEvent;
import com.freeactionscript.CollisionTest;
import flash.display.Stage;
public class AvoiderGame extends MovieClip
{
var theCallBackFunction:Function;
public static var enemyArray:Array;
public var enemy:Enemy
public var Background:gameBackground;
public var avatar:Avatar;
public var gameTimer:Timer;
private var _collisionTest:CollisionTest;
private var numStars:int = 80;
private var fireTimer:Timer; //causes delay between fires
private var canFire:Boolean = true; //can you fire a laser
public function AvoiderGame(callBack)
{
stage.addEventListener(Event.ADDED_TO_STAGE, init);
theCallBackFunction = callBack;
}
private function init(e:Event):void
{
Background = new gameBackground();
addChild(Background);
enemyArray = new Array();
var enemy = new Enemy(Math.round(1 + (500 - 1) * Math.random()), - 2, stage);
enemyArray.push(enemy);
addChild(enemy);
avatar = new Avatar(stage);
addChild(avatar);
avatar.x = stage.stageWidth / 2;
avatar.y = stage.stageHeight / 2;
for (var i:int = 0; i < numStars; i++)
{
stage.addChildAt(new Star(stage), 1);
}
_collisionTest = new CollisionTest();
gameTimer = new Timer(25);
gameTimer.addEventListener(TimerEvent.TIMER, onTick);
gameTimer.start();
fireTimer = new Timer(300, 1);
fireTimer.addEventListener(TimerEvent.TIMER, fireTimerHandler, false, 0, true);
fireTimer.start();
}
public function onTick(timerEvent:TimerEvent):void
{
if (Math.random() < 0.1)
{
trace('array length: ', AvoiderGame.enemyArray.length);
enemy = new Enemy(Math.round(1 + (500 - 1) * Math.random()), - 28, stage);
enemyArray.push(enemy);
addChild(enemy);
}
avatar.UpdateAvatar(canFire);
if (canFire == true)
{
canFire = false;
fireTimer.start();
}
avatar.StayOnScreen();
for each (var enemy:Enemy in enemyArray)
{
enemy.moveDown();
enemy.StayOnScreen();
if (_collisionTest.complex(enemy, avatar))
{
gameTimer.stop();
}
}
}
private function fireTimerHandler(e:TimerEvent) : void
{
//timer ran, we can fire again.
canFire = true;
}
}
}回答 3
Stack Overflow用户
回答已采纳
发布于 2012-11-19 04:52:18
public function AvoiderGame(callBack)
{
stage.addEventListener(Event.ADDED_TO_STAGE, init);
theCallBackFunction = callBack;
}应该是这样的
public function AvoiderGame(callBack)
{
this.addEventListener(Event.ADDED_TO_STAGE, init);
theCallBackFunction = callBack;
}在调用init函数时，不要忘记删除事件侦听器。
Stack Overflow用户
发布于 2012-11-19 04:51:03
如果未将显示对象添加到舞台或显示列表中已有的其它显示对象，则stage为null。当设置了stage并且可用时，将调度Event.ADDED_TO_STAGE。
Stack Overflow用户
发布于 2012-11-19 04:52:33
当您创建AvoiderGame对象时，它将触发构造函数。此时，该对象不会添加到舞台或显示列表中的任何对象，因此它将不会有任何对舞台的引用。
可以将侦听器添加到ADDED_TO_STAGE事件，也可以在手动将其添加到舞台之前调用自定义init方法。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/13444408
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