Delay in matching game giving error #2007

Question

I'm using a tutorial I found on Google - which works well. However, I have a few issues to make it work how I would like.

I tried to get the second card to hang on for a short time, so the kid (player) can see the match when there is a match.

Unfortunately, my code gave me a TypeError: Error #2007: Parameter child must be non-null runtime error in my matching game, and when I click on a new card before the set is removed the matching couple is turned back and the new clicked card is removed (on its own). I would appreciate any help.

This is the error and after that my code:

  TypeError: Error : Parameter child must be non-null.
        at flash.display::DisplayObjectContainer/removeChild()
        at MatchingGameObject9/remove_tiles()
        at flash.events::EventDispatcher/dispatchEventFunction()
        at flash.events::EventDispatcher/dispatchEvent()
        at flash.utils::Timer/tick()

package {
  import flash.display.*;
  import flash.events.*;
  import flash.text.*;
  import flash.utils.getTimer;
  import flash.utils.Timer;


  public class MatchingGameObject9 extends MovieClip {
      // game constants
        private static const boardWidth:uint = 6;
      private static const boardHeight:uint = 5;
      private static const cardHorizontalSpacing:Number = 87;
      private static const cardVerticalSpacing:Number = 87;
      private static const boardOffsetX:Number = 20;
      private static const boardOffsetY:Number = 45;
      private static const pointsForMatch:int = 100;
      private static const pointsForMiss:int = -5;

      private var firstCard:Card;
      private var secondCard:Card;
      private var cardsLeft:uint;
      private var gameScore:int;
      private var gameStartTime:uint;
      private var gameTime:uint;
      private var pause_timer:Timer;
      private var gameScoreField:TextField;
      private var gameTimeField:TextField;

      public function MatchingGameObject9():void {
        // make a list of card numbers
        var cardlist:Array = new Array();
        for(var i:uint=0;i<boardWidth*boardHeight;i++) {
            cardlist.push(i);

        }

        // create all the cards, position them, and assign a randomcard face to each
        cardsLeft = 0;
        for(var x:uint=0;x<boardWidth;x++) { // horizontal
            for(var y:uint=0;y<boardHeight;y++) { // vertical
                var c:Card = new Card(); // copy the movie clip
                c.stop(); // stop on first frame
                c.x = x*cardHorizontalSpacing+boardOffsetX; // set position
                c.y = y*cardVerticalSpacing+boardOffsetY;
                var r:uint = Math.floor(Math.random()*cardlist.length); // get a random face
                c.cardface = cardlist[r]; // assign face to card
                cardlist.splice(r,1); // remove face from list
                c.addEventListener(MouseEvent.CLICK,clickCard); // have it listen for clicks
                c.buttonMode = true;
                addChild(c); // show the card
                cardsLeft++;
            }
        }

        gameScoreField = new TextField();
        addChild(gameScoreField);
        gameScore = 0;
        showGameScore();

        gameTimeField = new TextField();
        gameTimeField.x = 450;
        addChild(gameTimeField);
        gameStartTime = getTimer();
        gameTime = 0;
        addEventListener(Event.ENTER_FRAME,showTime);
      }

      // player clicked on a card
      public function clickCard(event:MouseEvent) {
        var thisCard:Card = (event.target as Card); // what card?

        if (firstCard == null) { // first card in a pair
            firstCard = thisCard; // note it
            firstCard.gotoAndStop(thisCard.cardface+2); // turn it over

        } else if (firstCard == thisCard) { // clicked first card again
            firstCard.gotoAndStop(1); // turn back over
            firstCard = null;

        } else if (secondCard == null) { // second card in a pair
            secondCard = thisCard; // note it
            secondCard.gotoAndStop(thisCard.cardface+2); // turn it over

            // compare two cards
            if (Math.floor(firstCard.cardface/2) ==   Math.floor(secondCard.cardface/2)) {
                **pause_timer = new Timer(2000,1);
                 pause_timer.addEventListener(TimerEvent.TIMER_COMPLETE,remove_tiles);
                pause_timer.start();**
            }

        } else { // starting to pick another pair
            // reset previous pair
            firstCard.gotoAndStop(1);
            secondCard.gotoAndStop(1);
            secondCard = null;
            // select first card in next pair
            firstCard = thisCard;
            firstCard.gotoAndStop(thisCard.cardface+2);
        }
      }

      public function showGameScore() {
        gameScoreField.text = "ΣΚΟΡ: "+String(gameScore);
      }

      public function showTime(event:Event) {
        gameTime = getTimer()-gameStartTime;
        gameTimeField.text = "ΧΡΟΝΟΣ: "+clockTime(gameTime);
      }

      public function clockTime(ms:int) {
        var seconds:int = Math.floor(ms/1000);
        var minutes:int = Math.floor(seconds/60);
        seconds -= minutes*60;
        var timeString:String = minutes+":"+String(seconds+100).substr(1,2);
        return timeString;
      }
      **public function remove_tiles(event:TimerEvent) {
        removeChild(firstCard);
                removeChild(secondCard);
                // reset selection
                firstCard = null;
                secondCard = null;
                // add points
                gameScore += pointsForMatch;
                showGameScore();
                // check for game over
                cardsLeft -= 2; // 2 less cards
                if (cardsLeft == 0) {
                    MovieClip(root).gameScore = gameScore;
                    MovieClip(root).gameTime = clockTime(gameTime);
                    MovieClip(root).gotoAndStop("gameover");
                   pause_timer.removeEventListener(TimerEvent.TIMER_COMPLETE,remove_tiles);
                    } else {
                    gameScore += pointsForMiss;
                    showGameScore();
            }**
  }
}

Answer 1

I think you need to organize removing differently. Something like:

var removalQueue:Array = new Array;

addEventListener(Event.ENTER_FRAME, onRemove);

function onRemove(e:Event):void
{
    if (!removalQueue.length) return;

    var anEntry:Object = removalQueue[0];

    if (getTimer() < anEntry['time']) return;

    // Delete entry from queue.
    removalQueue.shift();

    removeChild(anEntry['first']);
    removeChild(anEntry['second']);

    gameScore += anEntry['score'];
    cardsLeft -= 2;

    // The rest of your code...
}

So when you have two matching cards you just need to push an appropriate entry to the queue:

var anEntry:Object =
{
    "time": getTimer() + 2000,
    "first": firstCard,
    "second": secondCard,
    "score": pointsForMatch
}

removalQueue.push(anEntry);