AS3: Timeline navigation with gotoAndStop(); throws unexpected null object error

[Swyze]

Here's my code. It seems I can't address the stage. I get a null object reference error at gotoAndStop(3);

private function  exitInvitation(e: MouseEvent😞 void {
simpleBack.removeEventListener(MouseEvent.CLICK, exitInvitation);
removeChild(simpleBack);

gotoAndPlay(3);
}

I'm moving from frame 10 to frame 3. This is clearly a bug. Not even code written on the timeline works. What do I have to listen for to know that my stage object is available?

I've tried adding:

addEventListener(Event.ADDED_TO_STAGE, init);

private function init(e:Event😞void
{
  removeEventListener(Event.ADDED_TO_STAGE, init);
  gotoAndPlay(3);
}

Sadly, it doesn't work. I have no idea why other buttons work in my AIR app, but this doesn't. Why is frame 3 null?

[kglad]

frame 3's not null.  your scope is.

what's this show:

private function  exitInvitation(e: MouseEvent😞 void {
simpleBack.removeEventListener(MouseEvent.CLICK, exitInvitation);
removeChild(simpleBack);
trace(this);
this.gotoAndPlay(3);
}

[Swyze]

Thx, but unfortunately, it didn't work. Here's what I have:

        public function  exitInvitation(e: MouseEvent): void {

            sendInviteBTN.removeEventListener(MouseEvent.CLICK, checkInvitation);

            simpleBack.removeEventListener(MouseEvent.CLICK, exitInvitation);

            removeChild(simpleBack);

            if (displayScore != null && contains(displayScore)) {

            removeChild(displayScore);

            }

            trace(this);

            this.gotoAndPlay(3);

            scoreTXT2.text = "" + userScore;

            usernameTXT.text = "" + username;

        }

This is what I'm getting:

[object Main]

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at Main/frame3()[Main::frame3:2]

    at flash.display::MovieClip/gotoAndPlay()

    at Main/exitInvitation()

Line 637 contains this.gotoAndPlay(3);

I have similar code for other buttons and everything works fine there.

[kglad · Accepted solution]

that means you have code on line 2 frame 3 of your fla's timeline that's trying to reference a null object.  ie, check your timeline, not the class code.

[Swyze]

Yes, you were right. The problem is, that the timeline code referred to a button that's on the stage, but I looked into the code and I don't call for its removal. It disappears on it's own, it seems, which is pretty weird. So I press a button at frame 3 that goes to  frame 9, and when I press the back button, it goes back to frame 3. Except, somehow, one of my buttons located on the stage gets removed, but I don't use removeChild along the way, so I have no idea how animate cc can remove a button that was placed there physically and not throughout code.

[kglad]

unless that button is created on frame 3, or is never removed, that problem is predicable.

(p.s when using the adobe forums, please mark helpful/correct responses, if there are any.)

[Swyze]

What you're saying is, it's better to create them dynamically and then remove them from the stage along with  eventlisteners? I susually, do that, but sometimes placing them manually on stage is more comfortable.

This button doesn't exist on frames 1 and 2, and is "only" located on frame 3 (it's not added dynamically).

[kglad]

the less you use the timeline, the less chance of difficult to debug errors.

but if an object only exists on one frame (and therefore is not tweened), i wouldn't expect that error.

[Swyze]

It's not. It's a completely static button without any timeline animation, or any animation whatsoever, but when I click back button at frame 9, the button on frame 3 literally disappears from the stage. Is there any way to trace an object located on a  different frame we're currently at? I've looked throught the code and didn't see anything that would remove the butto or switched its visible property to false.

[kglad]

you can't reference it from a frame where it doesn't exist.

you can enumerate all the objects on the main timeline when you return to frame 3 and see that it is still there, but has lost its previous reference (ie, instance name):

for (var i:int=0;i<this.numChildren;i++){

trace(this.getChildAt(i),this.getChildAt(i).name);

}