Actionscript 3: gotoAndStop

actionscriptactionscript-3buttonflashframe

I have a project in Flash CS3 that's giving me a bit of trouble. I have a movieclip, and in that movieclip, I have a button. The movieclip is named bg and the button tohallway_btn. My coding is on the stage on a layer, not on classes or in a package, or anything of that sort. This is my coding:

bg.tohallway_btn.addEventListener(MouseEvent.CLICK, tohallwayClick);
function tohallwayClick(event:MouseEvent):void{
        gotoAndStop (141);
    }

It seems simple enough, yet when I debug and the button is clicked, the flash player freezes over. I have absolutely no idea what's causing it to do this.

I get a type error in output as well:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Camille_fla::MainTimeline/enterF()[Camille_fla.MainTimeline::frame140:130]

Any help is appreciated.

Best Answer

An onEnterFrame listener was called and not removed that was referencing an object (bg) that was not on the stage after the goto call.

function tohallwayClick(event:MouseEvent):void {
    **removeEventListener(Event.ENTER_FRAME, enterF);**
    gotoAndStop(141);
}

Tracking it down

At first I thought this was a coercion bug where null was getting coerced to "null" and a test of "null" == null was passing. It's not. I was close, but so very, very wrong. Sorry about that!

I've since done lots of fiddling on wonderfl.net and tracing through the code in mx.rpc.xml.*. At line 1795 of XMLEncoder (in the 3.5 source), in setValue, all of the XMLEncoding boils down to

currentChild.appendChild(xmlSpecialCharsFilter(Object(value)));

which is essentially the same as:

currentChild.appendChild("null");

This code, according to my original fiddle, returns an empty XML element. But why?

Cause

According to commenter Justin Mclean on bug report FLEX-33664, the following is the culprit (see last two tests in my fiddle which verify this):

var thisIsNotNull:XML = <root>null</root>;
if(thisIsNotNull == null){
    // always branches here, as (thisIsNotNull == null) strangely returns true
    // despite the fact that thisIsNotNull is a valid instance of type XML
}

When currentChild.appendChild is passed the string "null", it first converts it to a root XML element with text null, and then tests that element against the null literal. This is a weak equality test, so either the XML containing null is coerced to the null type, or the null type is coerced to a root xml element containing the string "null", and the test passes where it arguably should fail. One fix might be to always use strict equality tests when checking XML (or anything, really) for "nullness."

Solution

The only reasonable workaround I can think of, short of fixing this bug in every damn version of ActionScript, is to test fields for "null" and escape them as CDATA values.

CDATA values are the most appropriate way to mutate an entire text value that would otherwise cause encoding/decoding problems. Hex encoding, for instance, is meant for individual characters. CDATA values are preferred when you're escaping the entire text of an element. The biggest reason for this is that it maintains human readability.

Best Answer

Related Solutions

R – In Flash: gotoAndStop and nested MovieClip issues

Actionscript – How to pass “Null” (a real surname!) to a SOAP web service in ActionScript 3

Tracking it down

Cause

Solution

Related Topic