What code in as-3 to use to allow seekbar to be moved by user? - actionscript-3

Question

I'm creating a simple music player which will play just one song. Stage timeline has got just one frame. There is main graphic for player which is movieClip_1 (it has 4 frames in it's own timeline) and that works ok. I've got button (button_2) which starts and pauses the song and the movieClip_1 (works ok). And i also have got a graphic (it's called tube - i have changed it to movie clip, it has got one frame inside it's timeline) as a seekbar component which I just want it to move correspondingly to channel.position of this song on the x axis which it does but gives me triple error of:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
Debug points at this line:
tube.x = (chan.position/song.length) * 83;
I would really appreciate a tip regarding error and also what method to use in order for user to be able to navigate (with mouse) through song by moving tube on x axis and going to different part of song. I read about .startDrag and .stopDrag would that be good idea with my present code?
My code so far:
movieClip_1.stop();
var itsstoped:Boolean;
var youpausedit:Boolean;
var counter:Timer = new Timer(100);
var chan:SoundChannel;
var song:Sound = new Sound();
song.load(new URLRequest("wmc2.mp3"));
song.addEventListener(Event.COMPLETE, soundloaded);
function soundloaded(event:Event)
{
trace("Song has been loaded.");
}
counter.addEventListener(TimerEvent.TIMER,countcounter);
itsstoped = true;
youpausedit = false;
button_2.addEventListener(MouseEvent.CLICK, presser);
function presser(event:MouseEvent):void
{
if(itsstoped == true && youpausedit == true)
{
movieClip_1.gotoAndPlay(1);
chan = song.play(chan.position);
itsstoped = false;
}
else if(itsstoped == false)
{
movieClip_1.gotoAndStop(1);
chan.stop();
itsstoped = true;
youpausedit = true;
}
else if(itsstoped == true && youpausedit == false)
{
movieClip_1.gotoAndPlay(1);
chan = song.play();
counter.start();
itsstoped = false;
}
}
function countcounter(e:TimerEvent):void
{
trace(chan.position/song.length);
var percentage:uint = 100 * (chan.position / song.length);
trace(percentage);
if(percentage == 100)
{
movieClip_1.gotoAndStop(1);
itsstoped = true;
youpausedit = false;
counter.stop();
}
}
tube.buttonMode = true;
tube.useHandCursor = true;
addEventListener(Event.ENTER_FRAME, movewhenplay);
function movewhenplay(e:Event):void
{
tube.x = (chan.position/song.length) * 83;
}

Answer 1

Regarding the error, you're accessing an object that has yet to be instantiated, i.e. there is no data to fetch as it does not exist.
As for the searchbar, I'm guessing you're using some kind of mask for the search bar, as you're using its x position to display the song position. I would suggest you instead use its width parameter, and set the center point to the far left.
To be able to then search through the song, you can add a copy of this searchbar, place it on top of the first one. Set its alpha to 0, to make it invisible, but still clickable. Add mouseEvent listeners to that, and when the user clicks it, you can set the song to play from the position which you can calculate using mouseX relevant to the invisible search bar.
I.e. if you want the clicked position in percents
percent = (mouseX - invisiSearchBar.x) / invisiSearchbar.width