Question

This question is related to ActionScript 3.0 and Flash CS6

I am trying to make an object shake a bit in a certain for some seconds. I made it a “movieclip” and made this code:

import flash.events.TimerEvent;

var Machine_mc:Array = new Array();

var fl_machineshaking:Timer = new Timer(1000, 10);
fl_machineshaking.addEventListener (TimerEvent.TIMER, fl_shakemachine);
fl_machineshaking.start ();


function fl_shakemachine (event:TimerEvent):void {


 for (var i = 0; i < 20; i++) {

  Machine.x += Math.random() * 6 - 4;
  Machine.y += Math.random() * 6 - 4;
 }

}

When testing the movie I get multiple errors looking exactly like this one:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at Historieoppgave_fla::MainTimeline/fl_shakemachine()
    at flash.utils::Timer/_timerDispatch()
    at flash.utils::Timer/tick()

Also, the object doesnt shake, but it moves steadily upwards to the left a bit every tick.

To the point:
I wish to know how I stop the script after the object is not in the stage/scene anymore and also how to make it shake around, as I do not see what is wrong with my script, please help, thank you ^_^

Answer 1

You have to remember the original start position and calculate the shake effect from that point. This is my shake effect for MovieClips. It dynamically adds 3 variables (startPosition, shakeTime, maxShakeAmount) to it. If you use classes, you would add them to your clips.

import flash.display.MovieClip;
import flash.geom.Point;

function shake(mc:MovieClip, frames:int = 10, maxShakeAmount:int = 30) : void 
{
    if (!mc._shakeTime || mc._shakeTime <= 0)
    {
        mc.startPosition = new Point(mc.x, mc.y);
        mc._shakeTime = frames;
        mc._maxShakeAmount = maxShakeAmount;
        mc.addEventListener(Event.ENTER_FRAME, handleShakeEnterFrame);
    }
    else
    {
        mc.startPosition = new Point(mc.x, mc.y);
        mc._shakeTime += frames;
        mc._maxShakeAmount = maxShakeAmount;
    }
}

function handleShakeEnterFrame(event:Event):void
{
    var mc:MovieClip = MovieClip(event.currentTarget);
    var shakeAmount:Number = Math.min(mc._maxShakeAmount, mc._shakeTime);
    mc.x = mc.startPosition.x + (-shakeAmount / 2 + Math.random() * shakeAmount);
    mc.y = mc.startPosition.y + (-shakeAmount / 2 + Math.random() * shakeAmount);

    mc._shakeTime--;

    if (mc._shakeTime <= 0)
    {
        mc._shakeTime = 0;
        mc.removeEventListener(Event.ENTER_FRAME, handleShakeEnterFrame);
    }
}

You can use it like this:

// shake for 100 frames, with max distance of 15px
this.shake(myMc, 100, 15);

BTW: In Flash, you should enable ‘permit debugging’ in your ‘publish settings‘ to have more detailed errors. This also gives back the line numbers where your code is breaking.

---

update:
Code now with time / maximum distance separated.