Flash CS3 null reference to button/mc after returning to Frame

Question

I've been researching this issue for hours and while I've found somewhat similiar situations, i have yet to find a simple fix. Basically I have a timeline where some animation plays. Eventually I get to my main game screen (frame 256) where a stop(); is called and the user then gets to click on one of 3 doors. Clicking on any door takes the user ahead a bunch of frames and they get to play a game. Once the game is done or the user clicks back, it takes the user back to the original frame (frame 256) and every single time it does this, it says my "upDoor" is a null reference and then the upDoor button(instance of upStairsDoor button) is no longer on the stage.

This seems to happen regardless of which door the user picks first. If the user picks the upDoor and plays the minigame there or picks the outsideDoor and plays that specific minigame, when the user returns to this frame (frame 256), it throws this error on the door and then of course because it throws an error, nothing else works at that point and I have to exit the game.

It's not a typo! Please don't suggest I check my instance names. As I mentioned, the door works fine the first time you get to the frame, it's just when you go back to it. I've read that it might have to do with the garbage collector but when we return to the frame, shouldn't it recreate all of the instances that I've placed to the stage? It doesn't error on ANY other button or movieClip that I've dragged to the stage, only this one particular door.

I forgot to mention that it's error'ing on a line of code that references the upDoor button. I have these lines of code here...(frame 256)

if (downDoor.enabled) {
    downDoor.enabled = false;
}
if (upDoor.enabled) {
    upDoor.enabled = false;
}
if (outDoor.enabled) {
    outDoor.enabled = false;
}

What these do is disable the doors until the user clicks another object on the screen which then runs a function that sets all the doors to enabled. The error in question is saying I can't access a property of a null reference.

The best fix IMHO is screw timeline AS IS, because when you do a gotoAndStop() or other frame change, the old frame is DESTROYED and all links are invalidated, so when you return to that frame, there's no downDoor anymore, as well as no other objects accessible by the time you were on that frame before. — Vesper
If you are unable to drop timeline, then use parent MC's properties, like if (downDoorEnabled) {downDoorEnabled=false; if (downDoor) downDoor.enabled=false; }. Make sure you plan them beforehand, as these properties are not contained within one frame, and overwriting these might damage your SWF logic. Be warned though, that their syntax is not checked at compile time, so if you've made a typo somewhere while reading a property, the result will be "undefined" (or if that property hasn't yet been set), and writing to a wrong property will result in the right property's value unchanged. — Vesper
@Richard-Chase Where do these lines of code exist? What event handler are they within? — C. Parcell
I cant ditch the timeline. I have way too much done already. Its weird that it only breaks the one object and not any others. What if i created the objects programmatically? — Richard Chase

Richard Chase Richard Chase · Accepted Answer · 2014-12-17T04:41:58

Thanks for the input guys. What ended up being the solution for me was to implement all of the movieclips and buttons programatically when the frame loads and then remove them all when I switch frames. That way, everytime the frame is reloaded from a gotoAndPlay, everything gets re-created again.

Flash CS3 null reference to button/mc after returning to Frame

1 Answers