How do I call methods and properties from parent classes? - actionscript-3

Question

I'm new here (and also relatively new with AS3 as well), so bear with me.
I've only discovered OOP 2 weeks ago, and before then, I knew only the most rudimentary knowledge of AS3. So I did make a lot of improvement, but one thing's been bugging me.
I can never seem to call functions and methods from parent classes. Even with setters and getters, the child class always gives me an output error. It looks something like this.
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Axiom/clicked()
This is an AS3 project that I'm working on right now that is giving me this problem.
Here's some basic background of the project.
I have the main class, called Main, and some other classes, called Axiom and Textbox. Main creates Axiom into a movieclip (background) that's already present on the stage. Axiom creates Textbox when clicked. Axiom calls a method called mouseClick from Main (plays a sound), and Textbox calls some properties from Axiom (text for the textbox).
I have attempted to use
MovieClip(this.parent).mouseClick();
and declaring a new variable in the child class, like this.
private var main:Main;
...
main.mouseClick();
And this leads me to question - what am I doing wrong, and how should I do it properly?
Here are the classes for reference.
Main.as
package {
import flash.ui.Keyboard;
import flash.events.Event;
import flash.events.EventDispatcher;
import flash.display.MovieClip;
import flash.events.KeyboardEvent;
import flash.ui.Mouse;
import flash.events.MouseEvent;
public class Main extends MovieClip {
// sound
private var music:Music = new Music();
private var clickSound:Click = new Click();
// instructions
private var instructions:Instructions = new Instructions();
// mouse
private var cursor:Cursor = new Cursor();
// player
private var player:Player = new Player();
private var animationState:String = "standing";
private var directionState:String = "right";
// Axiom
private var axiom:Axiom = new Axiom();
// movement
private var rightPressed:Boolean = false;
private var leftPressed:Boolean = false;
private var upPressed:Boolean = false;
private var downPressed:Boolean = false;
private var xMovement:Number = 0;
private var yMovement:Number = 0;
private var speed:Number = 22;
private var friction:Number = 0.9;
private var rDoubleTapCounter:int = 0;
private var lDoubleTapCounter:int = 0;
private var dDoubleTapCounter:int = 0;
private var uDoubleTapCounter:int = 0;
private var doubleTapCounterMax:int = 5;
private var running:Boolean = false;
public function Main() {
// constructor code
// mouse
stage.addChild(cursor);
cursor.mouseEnabled = false;
Mouse.hide();
// instructions
instructions.x = 640;
instructions.y = 120;
stage.addChild(instructions);
// add player
player.x = 642;
player.y = 448.95;
player.gotoAndStop(directionState);
player.right.gotoAndStop(animationState);
addChild(player);
// add Axiom
axiom.x = 300;
axiom.y = -150;
back.addChild(axiom);
// keyboard events
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyPressed);
stage.addEventListener(KeyboardEvent.KEY_UP, keyReleased);
// music
music.play(0, int.MAX_VALUE);
// loop
stage.addEventListener(Event.ENTER_FRAME, loop);
}
private function loop(e:Event):void {
// set mouse
cursor.x = stage.mouseX;
cursor.y = stage.mouseY;
// set Movement to speed
if (rightPressed) {
if (upPressed) {
if (running || (rDoubleTapCounter <= doubleTapCounterMax && uDoubleTapCounter <= doubleTapCounterMax)) {
xMovement = speed * 2;
yMovement = speed * -2;
} else {
xMovement = speed;
yMovement = speed * -1;
}
} else if (downPressed) {
if (running || (rDoubleTapCounter <= doubleTapCounterMax && dDoubleTapCounter <= doubleTapCounterMax)) {
xMovement = speed * 2;
yMovement = speed * 2;
} else {
xMovement = speed;
yMovement = speed;
}
} else if (running || rDoubleTapCounter <= doubleTapCounterMax) {
xMovement = speed * 2;
} else {
xMovement = speed;
}
} else if (leftPressed) {
if (upPressed) {
if (running || (lDoubleTapCounter <= doubleTapCounterMax && uDoubleTapCounter <= doubleTapCounterMax)) {
xMovement = speed * -2;
yMovement = speed * -2;
} else {
xMovement = speed * -1;
yMovement = speed * -1;
}
} else if (downPressed) {
if (running || (lDoubleTapCounter <= doubleTapCounterMax && dDoubleTapCounter <= doubleTapCounterMax)) {
xMovement = speed * -2;
yMovement = speed * 2;
} else {
xMovement = speed * -1;
yMovement = speed;
}
} else if (running || lDoubleTapCounter <= doubleTapCounterMax) {
xMovement = speed * -2;
} else {
xMovement = speed * -1;
}
} else if (downPressed) {
if (dDoubleTapCounter <= doubleTapCounterMax || running) {
yMovement = speed * -2;
} else {
yMovement = speed * -1;
}
} else if (upPressed) {
if (uDoubleTapCounter <= doubleTapCounterMax || running) {
yMovement = speed * -2;
} else {
yMovement = speed * -1;
}
}
// double tap counter
if (rightPressed == false) {
rDoubleTapCounter++;
}
if (leftPressed == false) {
lDoubleTapCounter++;
}
if (downPressed == false) {
dDoubleTapCounter++;
}
if (upPressed == false) {
uDoubleTapCounter++;
}
// change labels
if (player.currentLabel != animationState) {
player.right.gotoAndStop(animationState);
}
// friction
xMovement *= friction;
yMovement *= friction;
// animationState and stop
if (Math.abs(xMovement) > 1) {
if (Math.abs(xMovement) > 22) {
animationState = "running";
running = true;
} else {
animationState = "trotting";
running = false;
}
} else {
animationState = "standing";
xMovement = 0;
}
// right or left facing
if (xMovement > 0) {
player.scaleX = 1;
} else if (xMovement < 0) {
player.scaleX = -1;
}
//movement
if (back.x >= back.width / 2 - 50) {
if (player.x >= 642 && xMovement > 0) {
player.x = 642;
back.x -= xMovement;
} else {
if (player.x <= player.width / 2 && xMovement < 0) {
xMovement = 0;
} else {
player.x += xMovement;
}
}
} else if (back.x <= 1280 - back.width / 2 + 50) {
if (player.x <= 642 - 30 && xMovement < 0) {
player.x = 642;
back.x -= xMovement;
} else {
if (player.x >= 1280 + 30 - player.width / 2 && xMovement > 0) {
xMovement = 0;
} else {
player.x += xMovement;
}
}
} else {
back.x -= xMovement;
}
}
private function keyPressed(e:KeyboardEvent):void {
if (e.keyCode == Keyboard.RIGHT) {
rightPressed = true;
} else if (e.keyCode == Keyboard.LEFT) {
leftPressed = true;
} else if (e.keyCode == Keyboard.DOWN) {
downPressed = true;
} else if (e.keyCode == Keyboard.UP) {
upPressed = true;
}
}
private function keyReleased(e:KeyboardEvent):void {
if (e.keyCode == Keyboard.RIGHT) {
rightPressed = false;
rDoubleTapCounter = 0;
} else if (e.keyCode == Keyboard.LEFT) {
leftPressed = false;
lDoubleTapCounter = 0;
} else if (e.keyCode == Keyboard.DOWN) {
downPressed = false;
dDoubleTapCounter = 0;
} else if (e.keyCode == Keyboard.UP) {
upPressed = false;
uDoubleTapCounter = 0;
}
}
public function mouseClick():void {
clickSound.play();
}
}
}
Axiom.as
package {
import flash.events.MouseEvent;
import flash.events.EventDispatcher;
import flash.display.MovieClip;
public class Axiom extends MovieClip {
private var speechBox:Textbox = new Textbox();
private var speech:String = "Something came out of that pop.";
private var main:Main;
public function Axiom() {
// constructor code
this.addEventListener(MouseEvent.CLICK, onClickStage);
this.addEventListener(MouseEvent.CLICK, clicked);
}
private function onClickStage(e:MouseEvent):void {
trace(e.target,e.target.name);
}
private function clicked(e:MouseEvent):void {
main.mouseClick();
stage.addChild(speechBox);
this.removeEventListener(MouseEvent.CLICK, clicked);
}
public function get words():String {
return speech;
}
public function removeThis():void {
this.addEventListener(MouseEvent.CLICK, clicked);
removeChild(speechBox);
}
}
}
Textbox.as
package {
import flash.events.MouseEvent;
import flash.display.MovieClip;
import com.greensock.TweenLite;
public class Textbox extends MovieClip{
private var axiom:Axiom;
private var main:Main;
public function Textbox() {
// constructor code
this.x = 40;
this.y = 360;
this.textBox.text = axiom.words;
TweenLite.from(this, 0.3, {x: "10", alpha: 0});
this.addEventListener(MouseEvent.CLICK, nextPage);
}
private function nextPage(e:MouseEvent):void{
main.mouseClick();
TweenLite.to(this, 0.3, {x: "-10", alpha: 0});
MovieClip(this.parent).removeThis();
}
}
}

Answer 1

Instead of trying to call functions of the parent (rarely a good idea), use Events instead.
In your Axiom Class:
package {
...import statements
public class Axiom extends MovieClip {
private var speechBox:Textbox = new Textbox();
private var speech:String = "Something came out of that pop.";
private var main:Main; //this shouldn't be here, ideally, Axiom knows NOTHING about the main class.
public function Axiom() {
// constructor code
this.addEventListener(MouseEvent.CLICK, onClickStage);
this.addEventListener(MouseEvent.CLICK, clicked);
}
private function onClickStage(e:MouseEvent):void {
trace(e.target,e.target.name);
}
private function clicked(e:MouseEvent):void {
//main.mouseClick(); // unneccesary
dispatchEvent(e); //the event you caught by performing a click will be dispatched again, so that the parent can react to it
stage.addChild(speechBox); //Axiom might not have access to the stage, addChild would suffice
this.removeEventListener(MouseEvent.CLICK, clicked);
}
public function get words():String {
return speech;
}
public function removeThis():void {
this.addEventListener(MouseEvent.CLICK, clicked);
removeChild(speechBox);
}
}
}
and in your Main Class
axiom.addEventListener(MouseEvent.CLICK, onAximClicked);
private function onAxiomClicked(e:MouseEvent):void{
//now you can use the parents (in this case an Object of the Main class) functions
mouseClick();
}