as3 Access to undefined property? - actionscript-3

Can someone help me to find out why I'm getting the error message "Access to undefined property: removeChild(goBack)" on the following snipped?
BTW, this is for flash CS4
function nameOfFunction() {
var goBack:backButton_mc = new backButton_mc();
goBack.x = 10;
goBack.y = 700;
goBack.back_text.text = myXML.*[buildingName].NAME;
goBack.name = "backBtn";
goBack.buttonMode = true;
addChild(goBack);
goBack.addEventListener(MouseEvent.CLICK, anotherFunction);
}
function anotherFunction(e:MouseEvent):void {
removeChild(goBack);
}

You are wrong with the scope. (surprise :-D)
The variable goBack is just defined inside of "nameOfFunction", when you try to access this from a another function like "anotherFunction" it will not exists anymore (even if it is on the display list)
There are different possibilities to solve this problem:
function anotherFunction(e:MouseEvent):void {
removeChild(e.currentTarget);
}
Or the best way would be: promote goBack as a class member of the class holding both functions. (Or if you don't use classes make goBack "global".)

Hippo is correct, but I feel it is important to explain a little more.
You created a local variable, i.e. var someVariable:DataType; within a function. This means that that variable will only be available to objects in the scope (inside) of the function (local to), and it will only last for the lifetime of the function. Soon as that function has ran the code is gone until ran again. It looks like you are probable programming directly inside the flash IDE on the time-line, which is fine, but, if you were using a document class, you could merely declare you variable in the Class scope just above the constructor function, and then set the value in the same function that your using now. This way, the reference to the variable doesn't exist within the function, it is merely set from within. This will allow that variable to be accessed from anywhere in the same class even if set to private.
This may help:
//Frame 1, Actions layer
//Slap goBack right onto the root / stage
var goBack:MovieClip;
/*
I noticed you had this data-typed differently,
i prefer to type to an interface, not an implementation.
Since your class is a movieclip in the library it extends
MovieClip and therefor IS A MovieClip, but ok either way.
*/
function nameOfFunction():void
{
goBack = new backButton_mc();
goBack.x = 10;
goBack.y = 700;
goBack.back_text.text = myXML.*[buildingName].NAME;
goBack.name = "backBtn";
goBack.buttonMode = true;
addChild(goBack);
goBack.addEventListener(MouseEvent.CLICK, anotherFunction);
}
function anotherFunction(e:MouseEvent):void
{
removeChild(goBack);
}
Scope is very important and after a while very easy to tackle. Stick with it, experiment, read up on conventions and standards that can help your development and get to loving the DocumentClass becuase even though it may be daunting to some at first, once you learn it and get used to it, it so hard to go back to programming in the flash IDE on the timeline, where I believe only display objects and audio have any place being.

Related

Check the existence of an object instance

I'm surprised I don't know how to do this, but as it turns out I really don't; simply put, I'm trying to make a side-scrolling shooter game, a basic one and in it, I have 50 stars spawned on-screen through a "for" loop upon the game starting. There is a function which does this and a listener is at the beginning. Problem is, when you lose the game and go back to main menu, 50 more stars would be spawned, which isn't what I want. So, I'm trying to make an "if" statement check at the beginning, so that the game checks whether there is an instance/movie clip of the star object/symbol before determining whether the function that spawns stars should be called out with a listener. So, how do I do this? I looked through some other checks and they didn't help as the codes presented were vastly different there and so I'm just getting errors.
Let me know if a better explanation is needed or if you would like to see some of the code. Note that the game overall already has a lot of code, so just giving all of it would probably not be helpful.
I suggest you rethink your approach. You're focusing on whether stars have been instantiated. That's ok but not the most basic way to think about it.
I would do this instead
private function setup():void{
loadLevel(1);
addListeners();
loadMusic();
// etc...
// call all functions that are needed to just get the app up and running
}
private function loadLevel(lev:int):void{
addStars();
// call all functions that are needed each time a new level is loaded
}
private function restartLevel():void{
// logic for restarting level,
// but this *won't* include adding star
// because they are already added
}
There are other ways to do this but this makes more sense to me than your approach. I always break my game functions into smaller bits of logic so they can be reused more easily. Your main workhorse functions should (IMHO) primarily (if not exclusively) just call other functions. Then those functions do the work. By doing it this way, you can make a function like resetLevel by assembling all the smaller functions that apply, while excluding the part about adding stars.
Here's what I did to solve my problem... Here's what I had before:
function startGame():void
{
starsSpawn();
//other code here
}
This is what I changed it to:
starsSpawn();
function startGame():void
{
//other code here
}
when you said existance, so there is a container, i named this container, (which contain stars , and stars was added to it) as starsRoot, which absolutely is a DisplayObject (right?)
now, to checking whole childrens of a DisplayObject, we have to do this :
for (var i:int=0; i<starsRoot.numChildren; i++) {
var child = starsRoot.getChildAt[i];
}
then, how to check if that child is really star!?
as you said
whether there is an instance/movie clip of the star
so your stars's type is MovieClip, and they don't have any identifier (name), so how to find them and make them clear from other existing movieclips. my suggestion :
define a Linkage name for stars from library, thats a Class name and should be started with a capital letter, for example Stars
now, back to the code, this time we can check if child is an instance of Stars
for (var i:int=0; i<starsRoot.numChildren; i++) {
var child = starsRoot.getChildAt[i];
if (child is Stars) {
// test passed, star exist
break;
}
}

How can i get a function to use any movie clip?

I'm a little lost in understanding this kind of function, i get the feeling this has been asked a thousand times but cannot find an explanation of what the code is doing.
Basically i just want a movie clip with instance name box to do something, then reuse the function for other movie clips afterwards
a little like this, but working.
Many Thanks
//my function to be used on "instance name" box
myfunc (box);
function myfunc ();
{
while (this is happening);
{
//in this case box.x = goes where ever i put it
.x = goes here
.y = goes here
}
}
Sorry it's not quite English, my communication skills are terrible
Sure you can do that. You give the function a parameter, then refer to a parameter to change its properties. With such a simple movement function it could accept a DisplayObject - a distant superclass of a MovieClip and thus a superclass to many other possible classes of those objects that can be displayed by Flash.
function myfunc(param:DisplayObject):void {
// no semicolon after declaring the function!
while (somethingIsHappening(param)) {
// why not call a query on that object?
param.x+=1; // move right by 1 pixel
}
}
You might want to look at this manual on ActionScript 3 syntax, and the following pages on variables, functions and classes, to learn more.

Assign super to variable in AS3

I have this:
public class Base {
public function whoAmI() {
trace("base");
}
}
public class Extended extends Base {
public function Extended() {
this.whoAmI() //prints extended
super.whoAmI() //prints base
var test = super;
test.whoAmI() //prints extended
}
public override function whoAmI() {
trace("extended");
}
}
The problem is when I do var test = super, it seems like this is assigned to test instead of super.
Is it possible to do the assignment so that test.whoAmI() prints "base"?
Edit: In the comments it is being said that using super in the way I propose would break overriding. I don't think that's the case. The way I am thinking of it, super could be used the same way as this. I understand that is not the way super is implemented, but using it that way would not break overriding as people are claiming. So for example the same way this is possible:
var test = this;
test.whoAmI();
This should be possible:
var test = super;
super.whoAmI();
It is obviously the choice of the language implementer to not do things this way, and I don't understand the reason why. It doesn't break things, but I guess it does make them more complicated.
I am not suggesting type-casting this to the super class. Obviously that wouldn't work.
You are thinking of "this" and "super" as 2 different instances, 2 different things but they in fact point to the same object (obviously) so at the end it's always "this". Using super is just a special keyword that allows the instance to point to the overrided definitions up the inheritance chain, it does not point to a different object. So "super" does correctly its job, it points to the instance and allow you each time you use it to access overrided definitions and that's it. There's of course no point on trying to store that keyword in a variable since in that case it just return correctly the instance it points to which is always "this".
It's simply a case of misunderstood inheritance principle and I've seen it before, super is mistaken for some kind of instance wrapper up the inheriatnce chain around the object "this" while it's in fact and always the same object.
No, this is not possible.
If this were possible, then overriding methods wouldn't be possible!
For example, take this function...
public function test(a:Object):void {
trace(a.toString());
}
You'd only get [object Object] back if your idea was how things worked.
Ok I understand what you mean your question is more about language definition and specification.
Look at this exemple in c# that explain how you can manage more precisely overriding in c# :
http://www.dotnet-tricks.com/Tutorial/csharp/U33Y020413-Understanding-virtual,-override-and-new-keyword-in-C
But
let's explain a litlle how it's work.
when you extend a class, it's like if you create an object composed of all the object in the inheritance tree so if B extends A and C extends B you have two objects like this:
(B+A) and (C+B+A) with hierarchy between each other B->A and C->B->A. Super is just a way to ascend in the hierachy.
When you cast a C in A for example. In memory you always have an object (C+B+A) but interpreted as A. When you override you just say that a method in child has an higher priority than in parent.
You can try downcasting this manually to any of your class's predecessors. The pointer will still be equal to this but the methods called will use the class table of the class used to downcast.
public class Extended extends Base {
public function Extended() {
this.whoAmI() //prints extended
super.whoAmI() //prints base
var test:Base = this;
test.whoAmI() //should print base
}
public override function whoAmI() {
trace("extended");
}
}
Should your Base extend something, which methods are known or the superclass is dynamic, and there is code that adds methods to prototype of a class, you might use such a downcast to call a superclass's method that might not be there at compile time, but make sure you first call hasOwnProperty in case of a dynamic class to determine whether a method or property exists.

Saving the state of a movieclip containing multiple movieclips inside

this is actually a noobish question, but is there a possible way to save a certain state of a movieclip?, example i dynamically added a movieclip called big_mc, then inside big_mc contains three(3) smaller movie called child_mc1 and child_mc2 and a close_big to remove big_mc from the stage, when i click either of child_mc1 and child_mc2, the child_mc will disappear prior to which child_mc i clicked.
so the scenario is when I click child_mc1 which remove itself from the scene, then next I'll click the close_big movieclip to remove big_mc from the stage and will save it's own state, so then the next time i run the SWF file and dynamically add big_mc to stage, child_mc1 would be still missing and child_mc2 would still be displayed (EVEN IF I CLOSE THE SWF FILE, the state should be saved). please help..much is appreciated.
code in main time line:
var big_mc:mother_mc = new mother_mc;
add_big_btn.addEventListener(MouseEvent.CLICK, call_big);
function call_big(e:MouseEvent):void
{
addChild(big_mc);
}
the code inside big_mc:
child_mc1.addEventListener(MouseEvent.CLICK, remove_child1);
child_mc2.addEventListener(MouseEvent.CLICK, remove_child2);
close_big.addEventListener(MouseEvent.CLICK, bye);
function remove_child1(e:MouseEvent):void
{
removeChild(child_mc1);
}
function remove_child2(e:MouseEvent):void
{
removeChild(child_mc2);
}
function bye(e:MouseEvent):void
{
this.parent.removeChild(this);
}
You want to start with SharedObject, which as Adobe puts it, "is used to read and store limited amounts of data on a user's computer or on a server". To save the "state" of the MovieClip is more complicated.
What about it do you want to save? The x property? Perhaps the alpha? EVERYTHING? Each object is stored in a default state in your swf. Library items in the Flash IDE are technically miniature classes, as evidenced by the way we instantiate them. Assuming you create something called customButton, you could spawn thousands of them onscreen (or one) like this:
var foo:customButton = new customButton();
Like a hand-written class, a copy of the customButton is created with all the properties you defined on it before you compiled it. If you want to change those properties, you have to address each and every one you want different.
Looking at this broadly, let's assuming you want to save the position of your button every time you load the swf. Load with getLocal(), and save with flush().
var settings:Object = SharedObject.getLocal("foo");
function updateState(e:Event):void {
myButton.x = settings.x;
myButton.y = settings.y;
}
function saveState():void {
settings.x = myButton.x;
settings.y = myButton.y;
settings.flush();
}
It's not impossible; there's simply no push-button solution for it. If you wanted, you could write a function which iterates over all DisplayObjects, and loads/saves each relavent property from/into your SharedObject. Might be overkill, though.

AS3 Object indexing causing Flixel misbehaviour--what's wrong with this code?

I'm getting my feet wet with AS3, Flixel and component/entity systems (yes, all at the same time), and my entities (which subclass FlxSprite) aren't being added correctly (i.e., not at all). I've just spent a good two hours nailing down the offending line. If I remove it, the rest of the game chugs along happily.
What's wrong with this code?
public function addComponent(c:Component):void
{
var type:String = Object(c).constructor.toString();
FlxG.log("type=" + type);
this._components[type] = c; // The evil line
FlxG.log("now type=" + _components[type]);
c.setData(this);
}
components is an Object field being used as a map/dictionary. type gets set to [class PlayerComponent]. Based on googling, this is valid and should work as intended.
Based on the output from the console, it's just bailing after that line--not crashing entirely. What's going on? More details gladly offered upon request.
I'm not certain about Component - not my forte - but I do know that FlxGroup and its children (which include FlxState) have a method called add() which adds children to them.
So if you have an FlxSprite, the correct way (in flixel) to add it to the chain of things to update/draw is to use that; you can add it directly to your state or to a group that is a child of the state.
Function docs: http://flixel.org/docs/org/flixel/FlxGroup.html#add()