Question

Okay, so I’ve recently been trying to get my head properly around OOP in AS3. Right now I have a really simple scenario where I’ve got a class, Paddle, which draws a rectangle. In my document class I create two instances of the Paddle class, paddle1 and paddle2.

I’ve also created a property for my Paddle class which I want to change the colour of the rectangle that it draws. I want to be able to adjust this property from the main class. I know I could do this by passing in attributes when instantiating the class but it seems like a property would be a better way, and now I want to know if this is the right way of thinking or not.

main class:

    package
{
    import flash.display.Sprite;
    import flash.events.Event;

    public class Engine extends Sprite 
    {
        private var paddle1:Paddle = new Paddle();
        private var paddle2:Paddle = new Paddle();

        public function Engine() 
        {
            paddle1.x = 30;
            paddle1.color = 0xFF00FF;
            stage.addChild(paddle1);

            paddle2.x = stage.stageWidth - 45;
            paddle2.color = 0xFF0000;
            stage.addChild(paddle2);
        }

    }

}

Paddle class:

package
{
    import flash.display.MovieClip;
    import flash.display.Shape;
    import flash.display.Graphics;
    import flash.events.Event;

    public class Paddle extends MovieClip
    {
        public var color:uint = 0xFFFFFF;

        public function Paddle() 
        {
            var child:Shape = new Shape();
            child.graphics.beginFill(color);
            child.graphics.drawRect(0, 260, 15, 80);
            child.graphics.endFill();
            addChild(child);
        }

    }

}

If changing the properties in this way is not the best way of doing things then of course say so. Otherwise, what am I doing wrong that it doesn’t work? Seems like it’s something to do with the order (by the time the main class changes the colour attribute, it’s already created the rectangle and it’s too late to change it?)

Thanks 😀

EDIT: realised it might help to say what happens when I execute this code. Basically changing the color attribute from the Engine class doesn’t change the colour of the rectangle and they both just stay white (FFFFFF)

Answer 1

The issue you’re having is that when you do:

new Paddle();

Your constructor code is run. What this means is that the Rectangle has already been drawn with the color defined at the top of the class. You’re then changing the color property after this, which as you can see has no effect.

I suggest you make a draw() function for your Paddle. It could accept a color and be used to draw the Rectangle. It might look like this:

public class Paddle extends MovieClip
{

    private var _child:Shape;


    public function Paddle() 
    {
        _child = new Shape();
        addChild(_child);
    }


    public function draw(color:uint):void
    {
        _child.graphics.clear();
        _child.graphics.beginFill(color);
        _child.graphics.drawRect(0, 260, 15, 80);
        _child.graphics.endFill();
    }

}

This way provides an advantage which is that you can modify the arguments of draw() to accept dimensions for your Rectangle or other elements that will affect the visuals. This will be cleaner and faster than having to add more properties to the class itself if you decide you want to do this.

You’re then able to do this:

var paddle1:Paddle = new Paddle();
var paddle2:Paddle = new Paddle();

paddle1.draw(0xFF00FF);
paddle2.draw(0xFF0000);