game design coding error - actionscript-3

Question

/Question/
I have been at this for about a week and still can't find the problem.
I used trace statements but I cant tell whether is this or that. As I am still quite still inexperienced myself. I am using Flash Develop. thanks.
/* This is the error I am getting
I am trying remove the dango once it gets destroyed and remove it again after the game ends */
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at mcDango/destoryDango()[J:\catchMeDango\mcDango.as:72]
at catchMeDango/checkEndGameCondition()[J:\catchMeDango.as:195]
at catchMeDango/gameLoop()[J:\catchMeDango\catchMeDango.as:171]
---------------------------------------------------------------------------------------
/*This is for catchMeDango doc */
package
{
import flash.display.Loader;
import flash.display.MovieClip;
import flash.events.Event;
import flash.events.KeyboardEvent;
import flash.events.TimerEvent;
import flash.net.URLRequest;
import flash.text.TextField;
import flash.utils.Timer;
/**
* ...
* #author
*/
public class catchMeDango extends MovieClip
{
public var skewerPlayer:MovieClip;
private var leftKeyIsDown:Boolean;
private var rightKeyIsDown:Boolean;
private var upKeyIsDown:Boolean;
private var downKeyIsDown:Boolean;
private var aDangoArray:Array;
private var aBlackDangoArray:Array;
public var scoreTxt:TextField;
public var lifeTxt:TextField;
public var menuEnd:mcEndGameScreen;
private var nScore:Number;
private var nLife:Number;
private var tDangoTimer:Timer;
private var tBlackDangoTimer:Timer;
private var menuStart:mcStartGameScreen;
private var startHow:Loader;
public function catchMeDango()
{
//hides the endGameScreen
menuEnd.hideScreen();
//Create loader object
var startLoader:Loader = new Loader();
//Add event listener to listen the complete event
startLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, startLoaded);
//Load our loader object
startLoader.load(new URLRequest("startGameScreen.swf"));
}
private function startHowToPlay(e:Event):void
{
//Create loader object
startHow = new Loader();
//Add event listener to listen the complete event
startHow.contentLoaderInfo.addEventListener(Event.COMPLETE, HowToPlay);
//Load our loader object
startHow.load(new URLRequest("howToPlay.swf"));
}
private function HowToPlay(e:Event):void
{
//add the how to play movie clip to stage
addChild(startHow);
startHow.addEventListener("BEGIN_GAME", playGameAgain);
}
private function startLoaded(e:Event):void
{
//Get a reference to the loaded movieclip
menuStart = e.target.content as mcStartGameScreen;
//Listen for start game event
menuStart.addEventListener("START_GAME", playGameAgain);
menuStart.addEventListener("HOW_TO_PLAY", startHowToPlay);
//Add to stage
addChild(menuStart);
}
private function playGameAgain(e:Event):void
{
//I had to remove this function becuase is was causing errors
//When I click on the "how to play" then go back to the start screen, it hides fine with no issues
//startHow.visible = false;
menuStart.visible = false;
//set keyboard control to false
leftKeyIsDown = false;
rightKeyIsDown = false;
upKeyIsDown = false;
downKeyIsDown = false;
//Initialize variables
aDangoArray = new Array();
aBlackDangoArray = new Array();
nScore = 0;
nLife = 1;
skewerPlayer.visible = true;
menuStart.hideScreen();
menuEnd.addEventListener("PLAY_AGAIN", playGameAgain);
menuEnd.hideScreen();
updateScoreText();
updateLifeText();
//trace ('Catch Me Dango Loaded');
//Set up listerners for when an key is pressed
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDown);
stage.addEventListener(KeyboardEvent.KEY_UP, keyUp);
//Set up a game loop listener
stage.addEventListener(Event.ENTER_FRAME, gameLoop)
//Create a timer object for Dango for every 1 second
tDangoTimer = new Timer(1000)
//Listen for timer ticks/intervals
tDangoTimer.addEventListener(TimerEvent.TIMER, addDango)
//Start timer object
tDangoTimer.start();
//Create a timer object for Black Dango for every 10 seconds
tBlackDangoTimer = new Timer(10000)
//Listen for timer ticks/intervals
tBlackDangoTimer.addEventListener(TimerEvent.TIMER, addBlackDango)
//start timer object
tBlackDangoTimer.start();
}
//Display Score Text (Starting form: 0)
private function updateScoreText():void
{
scoreTxt.text = "Score: " + nScore;
}
//Display Life Text (Starting from: 5)
private function updateLifeText():void
{
lifeTxt.text = "Life: " + nLife;
}
private function addBlackDango(e:TimerEvent):void
{
//create new black dango object
var newBlackDango:mcBlackDango = new mcBlackDango();
//Add our new black dango
stage.addChild(newBlackDango);
aBlackDangoArray.push(newBlackDango);
trace(aBlackDangoArray.length);
}
private function addDango(e:TimerEvent):void
{
//create new dango(enemy) object
var newDango:mcDango = new mcDango();
//Create enemy to the stage
stage.addChild(newDango);
//Add our new dango(enemy) to dango(enemy) array collection
aDangoArray.push(newDango);
trace(aDangoArray.length);
}
private function gameLoop(e:Event):void
{
playerContorl();
clampPlayerToStage();
checkDangosOffScreen();
checkSkewerHitsDango();
checkBlackDangosOffScreen();
checkSkwerHitsBlackDango();
checkEndGameCondition();
}
//HELP
private function checkEndGameCondition():void
{
//Check if the player has 0 life left
if (nLife == 0)
{
//Stop player movement
stage.removeEventListener(KeyboardEvent.KEY_UP, keyUp);
stage.removeEventListener(KeyboardEvent.KEY_DOWN, keyDown);
//Hide the player
skewerPlayer.visible = false;
//Stop spawning dango and black dango
tDangoTimer.stop();
tBlackDangoTimer.stop();
//Clear the dango currently on screen
for each(var dango:mcDango in aDangoArray)
{
//this destory function had to be removed as well. because it was destorying the dango twice when it was already removed from the stage.
//by commenting out this, it was able to destory and remove without any errors and only doing it once.
//Destory the dango the were curretly up to in the for loop
dango.destoryDango();
trace("black dango removed")
//Remove from dango from dango array
aDangoArray.splice(0, 1);
}
//Clear the black dango currently on screen
for each(var blackDango:mcBlackDango in aBlackDangoArray)
{
//Destory the dango tat were curretly up to in the for loop
blackDango.destoryBlackDango();
//Remove from dango from dango array
aBlackDangoArray.splice(0, 1);
}
//Stop the game loop
if (aDangoArray.length == 0 && aBlackDangoArray.length == 0)
{
stage.removeEventListener(Event.ENTER_FRAME, gameLoop);
}
//Show end game screen
menuEnd.showScreen();
}
}
// Checks if the Skewer Hits or makes conatct with the Black Dango
private function checkSkwerHitsBlackDango():void
{
//Loop through our current Black dango
for (var i:int = 0; i < aBlackDangoArray.length; i++)
{
//Get our current Black Dango in the loop
var currentBlackDango:mcBlackDango = aBlackDangoArray[i];
//Test if our skewer is hitting the black dango
if (skewerPlayer.hitTestObject(currentBlackDango))
{
//remove the current dango from stage
currentBlackDango.destoryBlackDango()
//Remove the dango from out dango array
aBlackDangoArray.splice(i, 1);
//Minus one to our score
nScore--;
updateScoreText();
//Minus one to our life
nLife--;
updateLifeText();
}
}
}
// Remove the black dango of the stage and from the array
private function checkBlackDangosOffScreen():void
{
//loop through all our black dango
for (var i:int = 0; i < aBlackDangoArray.length; i++)
{
//Get our current dango in the loop
var currentBlackDango:mcBlackDango = aBlackDangoArray[i];
//When dango starts on the top AND our curent enemy has gone past the bottom side if the stage
if (currentBlackDango.y > (stage.stageHeight + currentBlackDango.y / 2))
{
//Remove black dango (enemy) from array
aBlackDangoArray.splice(i, 1);
//Remove black dango (enemy) from stage
currentBlackDango.destoryBlackDango();
}
}
}
// Checks if the Skewer Hits or makes conatct with the Dango
private function checkSkewerHitsDango():void
{
//Loop through all our current dango
for (var i:int = 0; i < aDangoArray.length; i++)
{
//Get our current dango in the loop
var currentDango:mcDango = aDangoArray[i];
//Test if our skewer is hitting dango
if (skewerPlayer.hitTestObject(currentDango))
{
//remove the current dango from stage
currentDango.destoryDango()
//Remove the dango from out dango array
aDangoArray.splice(i, 1);
//Add one to our score
nScore++;
updateScoreText();
}
}
}
// Remove the dango of the stage and from the array
private function checkDangosOffScreen():void
{
//loop through all our dangos(enemies)
for (var i:int = 0; i < aDangoArray.length; i++)
{
//Get our current dango in the loop
var currentDango:mcDango = aDangoArray[i];
//When dango starts on the top AND our curent enemy has gone past the bottom side if the stage
if (currentDango.y > (stage.stageHeight + currentDango.y / 2))
{
//Remove dango (enemy) from array
aDangoArray.splice(i, 1);
//Remove dango (enemy) from stage
currentDango.destoryDango();
}
}
}
private function clampPlayerToStage():void
{
//If our player is to the left of the stage
if (skewerPlayer.x < skewerPlayer.width/2)
{
//Set our player to left of the stage
skewerPlayer.x = skewerPlayer.width/2;
} else if (skewerPlayer.x > (stage.stageWidth - (skewerPlayer.width / 2)))
//If our player is to the right of the stage
{
//Set our player to right of the stage
skewerPlayer.x = stage.stageWidth - (skewerPlayer.width / 2);
}
//If our player is to the top(up) of the stage
if (skewerPlayer.y < 0)
{
//Set our player to the top(up) of the stage
skewerPlayer.y = 0;
} else if (skewerPlayer.y > (stage.stageHeight - (skewerPlayer.height / 1)))
//If our player is to the bottom(down) of the stage
{
//Set our player to the bottom(down) of the stage
skewerPlayer.y = stage.stageHeight - (skewerPlayer.height / 1);
}
}
// right, left, top and bottom Key Functions
private function playerContorl():void
{
//if our left key is currently down
if (leftKeyIsDown == true)
{
//move our player to the left
skewerPlayer.x -= 5;
}
//if our right key is currently down
if (rightKeyIsDown)
{
//move our player to the right
skewerPlayer.x += 5;
}
//if our up key is currently down
if (upKeyIsDown)
{
//move our player to the top
skewerPlayer.y -= 5;
}
//if our down key is currently down
if (downKeyIsDown)
{
//move our player to the bottom
skewerPlayer.y += 5;
}
}
private function keyUp(e:KeyboardEvent):void
{
//if our left key is released
if (e.keyCode == 37)
{
//left key is released
leftKeyIsDown = false;
}
//if our right key is released
if (e.keyCode == 39)
{
//right key is released
rightKeyIsDown = false;
}
//if our up key is released
if (e.keyCode == 38)
{
//up key is released
upKeyIsDown = false;
}
//if our down key is released
if (e.keyCode == 40)
{
//down key is released
downKeyIsDown = false;
}
}
private function keyDown(e:KeyboardEvent):void
{
//if our left key is pressed
if (e.keyCode == 37)
{
//left key is pressed
leftKeyIsDown = true;
}
//if our right key is pressed
if (e.keyCode == 39)
{
//right key is pressed
rightKeyIsDown = true;
}
//if our up key is pressed
if (e.keyCode == 38)
{
//up key is pressed
upKeyIsDown = true;
}
//if our down key is pressed
if (e.keyCode == 40)
{
//right key is pressed
downKeyIsDown = true;
}
}
}
}
---------------------------------------------------------------------------------
/*This is for mcDango doc */
package
{
import flash.display.MovieClip;
import flash.events.Event;
/**
* ...
* #author
*/
public class mcDango extends MovieClip
{
private var nSpeed:Number;
private var nRandom:Number;
public function mcDango()
{
// listen for when the Dango is added to the stage
addEventListener(Event.ADDED_TO_STAGE, onAdd);
}
private function onAdd(e:Event):void
{
removeEventListener(Event.ADDED_TO_STAGE, onAdd);
init();
}
private function init():void
{ //Number of frames you have in Flash
var nDango:Number = 12;
//Pick random number between 1 and our number of enemies(dango)
var nRandom:Number = randomNumber(1, nDango)
//Setup our player of this enemey(dango) clip to pur random dango
this.gotoAndStop(nRandom);
//Setup our enemies(dango) start position
setupStartPosition();
}
private function setupStartPosition():void
{
//Pick a random speed for enemy(dango)
nSpeed = randomNumber(5, 10);
//Set your ramdon X postion
nRandom = randomNumber(9, 775);
//Start our enemy(dango) on the top side
this.y = -50;
//set random pos X
this.x = nRandom
//move our enmey(dango)
startMoving();
}
private function startMoving():void
{
addEventListener(Event.ENTER_FRAME, dangoLoop)
}
private function dangoLoop(e:Event):void
{
//Test what direction our enemy(dango) is moving in
//If our enemy(dango) is moving right
//Move our enemy(dango) down
this.y += nSpeed
}
public function destoryDango():void
{
//Remove dango from stage
parent.removeChild(this);
trace("the dango has been removed")
//Remove any event listeners in our enemy object
removeEventListener(Event.ENTER_FRAME, dangoLoop);
}
function randomNumber(low:Number=0, high:Number=1):Number
{
return Math.floor(Math.random() * (1+high-low)) + low;
}
}
}

Answer 1

Glancing at the code, looks like the problem is with following for-each-in loop
for each(var dango:mcDango in aDangoArray) {
//this destory function had to be removed as well. because it was destorying the dango twice when it was already removed from the stage.
//by commenting out this, it was able to destory and remove without any errors and only doing it once.
//Destory the dango the were curretly up to in the for loop
dango.destoryDango();
trace("black dango removed")
//Remove from dango from dango array
aDangoArray.splice(0, 1);
}
Check using
while(aDangoArray.length > 0) {
var dango = aDangoArray[0]
dango.destoryDango();
trace("black dango removed")
aDangoArray.splice(0, 1);
}

Answer 2

Well, it looks like the issue is when you try to access the parent.removeChild method. Maybe you already removed it from stage and it doesn't have a parent anymore. Try doing this:
public function destoryDango():void
{
//Remove dango from stage
if(parent != null)
parent.removeChild(this);
trace("the dango has been removed")
//Remove any event listeners in our enemy object
removeEventListener(Event.ENTER_FRAME, dangoLoop);
}