AS3 stage = null?

actionscript, actionscript-3, events, parent-child

Solution

public function AvoiderGame(callBack)
{
    stage.addEventListener(Event.ADDED_TO_STAGE, init);
    theCallBackFunction = callBack;
}

Should be something like

public function AvoiderGame(callBack)
{
    this.addEventListener(Event.ADDED_TO_STAGE, init);
    theCallBackFunction = callBack;
}

Don't forget to remove the event listener when the init function is called.

Problem

I've just tried to implement a menu system I saw a tutorial onto a game that I'm working on and it was all smooth sailing until I've now encountered a problem with the stage being set to null and I don't know how to stop it. The line that keeps breaking it is in the AvoiderGame.as file and is the `stage.addEventListener(Event.ADDED_TO_STAGE, init);` it keeps returning the following error ``` 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] ``` Currently the way I've programmed my game is so that it starts in States.as which contains the following code. ``` 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; } } } } ``` From there it will go into mainMenu.as until the user clicks play - inside mainMenu.as is the following code ``` 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; } } } ``` Now this is where it goes wrong - it goes into AvoiderGame.as and it then kicks me back with an error which I don't know how to fix - Could anyone advise me on how to fix it? ``` 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; } } } ```

Original source