Drag and Drop Game using AS3 - actionscript-3

Question

import flash.events.MouseEvent;
import flash.utils.Timer;
import flash.events.TimerEvent;
var wordArray:Array = [mc_clipA, mc_clipB];
var imgArray:Array = [Aimg, Bimg];
var posArray:Array = [ {x:816.15, y:396.05}, {x:518.3, y:410.05}];
var ClipA:MovieClip;
var ClipB:MovieClip;
var startXpositionClipA:Number;
var startYpositionClipA:Number;
var startXpositionClipB:Number;
var startYpositionClipB:Number;
wordArray[0].buttonMode = true;
wordArray[1].buttonMode = true;
wordArray[0].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipA);
wordArray[1].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
//Mouse Down Function for ClipA
function item_onMouseDownClipA(event:MouseEvent):void {
ClipA = MovieClip(event.currentTarget);
startXpositionClipA = ClipA.x;
startYpositionClipA = ClipA.y;
addChild(ClipA);
ClipA.startDrag();
stage.addEventListener(MouseEvent.MOUSE_UP, stage_onMouseUpClipA);
wordArray[0].removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipA);
wordArray[1].removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
}
//Mouse Up Function for ClipA
function stage_onMouseUpClipA(event:MouseEvent):void {
stage.removeEventListener(MouseEvent.MOUSE_UP, stage_onMouseUpClipA);
ClipA.stopDrag();
var indexClipA:int = wordArray.indexOf(ClipClipA);
var matchClipClipA:MovieClip = MovieClip(imageArray[indexClipA]);
if(matchClipClipA.hitTestPoint(ClipA.x, ClipA.y, true)) {
ClipA.x = positionArray[indexClipA].x;
ClipA.y = positionArray[indexClipA].y;
ClipA.removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownZip);
ClipA.buttonMode = false;
var tot=0;
tot=tot+10;
score.text="You scored: " + tot +" Points ";
var setTimer:Timer = new Timer(1000,60);
setTimer.addEventListener(TimerEvent.TIMER,doTask);
setTimer.start();
function doTask(event:TimerEvent) {
gotoAndStop(1,"Scene 2");
setTimer.stop();
}
}
else
{
ClipA.x = startXpositionClipA;
ClipA.y = startYpositionClipA;
wordArray[0].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipA);
wordArray[1].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
}
}
//Mouse Down Function for ClipB
function item_onMouseDownClipB(event:MouseEvent):void {
ClipB = MovieClip(event.currentTarget);
startXpositionClipB = ClipB.x;
startYpositionClipB = ClipB.y;
addChild(ClipB);
ClipB.startDrag();
stage.addEventListener(MouseEvent.MOUSE_UP, stage_onMouseUpClipB);
wordArray[0].removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipA);
wordArray[1].removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
}
//Mouse Up Function for ClipB
function stage_onMouseUpClipB(event:MouseEvent):void {
stage.removeEventListener(MouseEvent.MOUSE_UP, stage_onMouseUpClipB);
ClipB.stopDrag();
var indexClipB:int = wordArray.indexOf(ClipB);
var matchClipClipB:MovieClip = MovieClip(imageArray[indexClipB]);
if(matchClipClipB.hitTestPoint(ClipB.x, ClipB.y, true)) {
ClipB.x = positionArray3[indexTie].x;
ClipB.y = positionArray3[indexTie].y;
ClipB.removeEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
ClipB.buttonMode = false;
var tot=0;
tot=tot;
score.text="You scored: " + tot +" Points ";
var setTimer:Timer = new Timer(1000,60);
setTimer.addEventListener(TimerEvent.TIMER,doTask);
setTimer.start();
function doTask(event:TimerEvent) {
gotoAndStop(1,"Scene 2");
setTimer.stop();
}
}
else
{
ClipB.x = startXpositionClipB;
ClipB.y = startYpositionClipB;
wordArray[0].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipA);
wordArray[1].addEventListener(MouseEvent.MOUSE_DOWN, item_onMouseDownClipB);
}
}
This is regarding a drag n drop game. A particular object name will be displayed to the user then the user has to drag n drop the correct image to specified position and once the task is completed it will dynamically navigate to the next scene. For that i have used the timer class. I am getting this error in the scene 2 but in scene 1 the code runs perfectly.
The naming conventions are all correct but i still get the following error,
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at MethodInfo-1156()
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()
Can someone help me with this.

Answer 1

Your locally declared method "doTask" is removed right after the execution of the mouse listener. You should either create an anonymous inline listener
var setTimer:Timer = new Timer(1000,60);
setTimer.addEventListener(TimerEvent.TIMER, function(event:TimerEvent):void {
gotoAndStop(1,"Scene 2");
setTimer.stop();
});
setTimer.start();
Some like to do so but I am not a big fan of inline declaration. I would create a real method in my class as a listener.
private var setTimer:Timer;
function stage_onMouseUpClipB(event:MouseEvent):void {
...
setTimer = new Timer(1000,60);
setTimer.addEventListener(TimerEvent.TIMER,doTask);
...
}
function doTask(event:TimerEvent):void {
gotoAndStop(1,"Scene 2");
setTimer.stop();
}