I think of 2 approaches referring to some visual element like movieclip. So suppose i have b_mc ( name="b") lying inside a_mc on the stage :
1st approach :
var mc:MovieClip = a_mc.b_mc
2nd approach :
var mc:MovieClip = a_mc.getChildByName("b")
I generally use 1st approach. What can be good reason to go for 2nd approach. It sometimes seems useless to me, as it involves extra overhead to name the movieclips, when used dynamically.
Thanks
V.
a.getChildByName('b') is slower than getting a.b.
If you don't need to use names it makes no sense to use it, however some programmers might make use of the name, especially when generating content dynamically rather than through the Flash IDE, in which case having this function is helpful, so that the display list doesn't have to be traversed by a custom function (which it does with internal function anyway, ergo it is slower than a.b)
getChildByName is needed if you add something dynamically to a movieclip. For instance:
var mc1:MovieClip = new MovieClip();
var mc2:MovieClip = new MovieClip();
mc2.name = "foobar";
mc1.addChild(mc2);
trace(mc1.foobar); //undefined
trace(mc1["foobar"]); //undefined
trace(mc1.getChildByName("foobar")); //[object MovieClip]
I usually do mc1["foobar"] when referencing objects since that way it's easy to work with items such as mc1["foobar_" + i];
I rarely never use getChildByName since that requires a manual cast whenever you try to pass something as a movieclip/textfield or whatever :)
However, if you do create the instances from the flash editor, then I would usually reference them through some exported class and access them through
mc1.mc2.mc3.optionsView.visible
If you have a list of objects that you need to go through programmatically, getChildByName is great. It would assume you've also named them in some programmatic way to reindex them in the for loop. I can also think of a couple other good ways to use this, like pushing the names or objects in an array, so they wouldn't have to be related, just all have some property or method in common.
for(var i:int = 0;i<numOfMC;i++) {
theParent.getChildByName("child"+i).doSomething();
}
Related
I was actually looking for a way to pass by reference in AS3 but then it seemed that adobe and lots of people's understanding of pass by reference is different from what I have been taught at the university. I was taught java was pass by value and C++ allowed pass by reference.
I'm not trying to argue what pass by value and reference are. I just want to explain why I'm using pass by object in the question...
Back to the question, I would like to do something like:
public function swapCard(cardA:Cards, cardB:Cards) {
var temp:Cards = cardA;
cardA = cardB;
cardB = temp;
}
...
swapCard(c1, c2);
EDIT: adding two examples on how I'm using the swapCard function
1) in the process of swaping a card between player1 and player2's hand
swapCard(player1.hand[s], player2.hand[t]);
2) in the process of swaping a card between player1's hand and deck
swapCard(player1.hand[s], player1.deck[rand]);
In C++, we only need to add a symbol before the parameters to make it work (and we call THIS pass by reference). But in AS3, cardA and cardB are just pointers to the formal parameters. Here in the function, changing the pointers does not do anything to the formal parameters :(
I have been searching for hours but I couldn't find a way to without knowing all the properties of the Cards.
If I have to change the properties of the cards one by one then maybe I should change swapCard to a static function in class Cards? (because I don't want to expose everything to another class) I'm not sure if this is a good practice either. This is like adding a swap_cars function into class Cars. If I let this happen, what will be next? Wash car, lend car, rent car... I really want to keep the Cards class clean and holds only the details of the card. Is there a possible way to do this properly in AS3?
The kind of swap function that you're trying to implement is not possible in AS3. The input parameters are references to the input objects but the references themselves are passed by value. This means that inside the function you can change the cardA and cardB but those changes will not be visible outside the function.
Edit: I added this portion after you edited your question with sample usage.
It seems like you're trying to swap two objects in 2 different arrays at given array positions in each - you can create a function for this in AS3 but not the way you attempted.
One possible implementation is to pass the arrays themselves and the positions that you're trying to exchange; something like this:
// Assumes arrays and indices are correct.
public function SwapCards(playerHand:Array, playerCardIndex:int,
playerDeck:Array, playerDeckIndex:int):void
{
var tempCard:Card = playerHand[playerHandIndex];
playerHand[playerHandIndex] = playerDeck[playerDeckIndex];
playerDeck[playerDeckIndex] = tempCard;
}
Note that you still exchange references and the arrays themselves are still passed by reference (and the array references are passed by value - you could, if you wanted, change the arrays to new arrays inside this function but you wouldn't see new arrays outside). However, because the array parameters refer to the same arrays inside and outside the function, you can make changes to the contents of the array (or other array properties) and those changes will be visible outside.
This solution is faster than cloning the card because that involves allocating memory for a new Card instance (which is expensive) and that temporary instance will also have to be freed by the garbage collector (which is also expensive).
You mentioned in a comment that you pass cards down to lower levels of code - if you don't have a back reference to the arrays (and the positions of the cards), you will not be able to easily swap cards - in AS3, all input parameters are copies (either the copy of the value for primitive types or the copy of the reference for complex objects - changes to the input parameters in a function will not be visible outside).
EDIT: renaming the function from clone to copyFrom as pointed out by aaron. Seems like clone is supposed to be used as objA = objB.clone()
At this point, I'm adding a copyFrom() function in the Cards class such that
var temp:Cards = new Cards(...);
var a:Cards = new Cards(...);
...
temp.copyFrom(a);
...
temp will be copying everything from a.
public function swapCard(cardA:Cards, cardB:Cards) {
var temp:Cards = new Cards();
temp.copyFrom(cardA);
cardA.copyFrom(cardB);
cardB.copyFrom(temp);
}
I will wait for a week or so to see if there are any other options
You have some good answers already, but based on the comments back-and-forth with me, here's my suggestion (I use "left" and "right" naming because it helps me visualize, but it doesn't matter):
function swapCard(leftCards:Array, leftCard:Card, rightCards:Array, rightCard:Card):void {
var leftIndex:int = leftCards.indexOf(leftCard);
var rightIndex:int = rightCards.indexOf(rightCard);
leftCards[leftIndex] = rightCard;
rightCards[rightIndex] = leftCard;
}
Now you can swap the cards in the two examples you posted like this:
swapCard(player1.hand, player1.hand[s], player2.hand, player2.hand[t]);
swapCard(player1.hand, player1.hand[s], player1.deck, player1.deck[rand]);
However, note that while this swaps the cards in the arrays, it does not swap direct references to the cards in those arrays. In other words:
var a:Card = player1.hand[0];
var b:Card = player2.hand[0];
swapCard(player1.hand, a, player2.hand, b);
// does not change the references a and b, they still refer to the same card
a == player2.hand[0];
a != player1.hand[0];
b == player1.hand[0];
b != player2.hand[0];
Typically, this sort of thing is handled by dispatching a "changed" event so that any code that cares about the state of a player's hand array will know to re-evaluate the state of the hand.
There's a deep misunderstanding going on here. The question is about object reference but the PO is not trying to swap any Object reference at all.
The problem comes from the fact that the PO does not understand the difference between variable and objects. He's trying to swap variable/object reference which is not dynamically possible of course. He wants with a function to make the variable holding a reference to Object A, swap its object reference with another variable. Since Objects can be passed around but not variables (since they are just holders (not pointers)) the task is not possible without a direct use of the given variable.
To resume:
variables are not Objects!
variables hold a reference to an object.
variables cannot be passed in function or referenced in functions because THEY ARE NOT OBJECTS.
So i have narrowed down my problem to this:
i have two instances of a movieclip ("content1", "content2") added into two different other movieclips ("container1", "container2"). I want to remove them.
As soon as i remove one of them with this horrible command...
MovieClip(MovieClip(root).getChildByName("container1")).removeChild(MovieClip(MovieClip(root).getChildByName("container1")).getChildByName("content1"));
...the other instance of it changes its instance name to a generic one (like "instance25") and i can't access it anymore with getChildByName.
Can anyone explain this please?
I've never experienced that behaviour - regardless, what you can do is store reference to both before you remove them. This way, you won't need their original instance name to remove both:
var top:MovieClip = root as MovieClip;
var cotainer:MovieClip = top.container1;
var content1:MovieClip = container.getChildByName("content1");
var content2:MovieClip = container.getChildByName("content2");
container.removeChild(content1);
container.removeChild(content2);
Hopefully this answer gives you some hints for making your code much more readable as well.
I'm learning flex/flash and I'm lost on this one. I have used the "data" in a bunch of views and it works fine. For some reason it isn't working here.
I set a field to a string here:
function LoginLoaded (e:Event):void {
trace(e.target.data);
var ServerReturn:String;
ServerReturn = new String(e.target.data);
data.UserCommonReturnData = ServerReturn;
navigator.pushView(CommonPlaces, data);
}
and here in the common places view I try to load it back:
var CommonPlacesData:String = new String();
var CurrentSelect:String = new String();
CommonPlacesData = new String(data.UserCommonReturnData);
This gives the error "Access of undefined property data" I don't get it because calling on something like data.PickUpTime (also a string) works fine in other views.
The data begins in the first view like this:
[Bindable] public var User:ObjectProxy = new ObjectProxy();
User.ID = "2314084";
navigator.pushView(TaxiNowOrLaterView, User);
then in later views I call on it like this: (works fine)
var PickUpString:String = new String(data.ID);
Any help would be great!! Thanks!!!
There are few things about your code. First, you really should make it a habit to name the identifiers as appropriate to the language. Identifiers that start with the capital letter and subsequently use minuscule letters for the rest of the logical part of the word (system alternatively known as PascalCase) is employed to only name classes. The rest of identifiers should use camelCase (similar to PascalCase, but the first letter isn't capitalized)**. This greatly reduces the effort at understanding your code. A seasoned AS3 programmer would interpret your code as follows:
// Static constant (!) ID of the class User is assigned (?) a value of "2314084"
User.ID = "2314084";
// invoke a method pushView of a local variable navigator with arguments
// of which first is the class TaxiNowOrLater, the second is the class User
navigator.pushView(TaxiNowOrLaterView, User);
while, perhaps, you didn't mean it.
new String();
In the context of AS3 makes no sense at all. Strings are never references, are immutable and have literal syntax the majority of programmers agreed upon. The code above is identical to "". In the similar way, new String(anotherString) has exact same effect as anotherString.
Your question: event.target may be many different things, some of them may have property called "data" and some may not. The general approach to this problem is that you need to cast the value of event.currentTarget or event.target to the type you expect to dispatch the event. Suppose you are expecting an event from an instance of a Button class, then:
private function clickHandler(event:MouseEvent):void {
if (Button(event.currentTarget).enabled) // do things
}
This will not protect you from an error, if the same event was dispatched by an object, which is not a button, but will make the error reporting more conscious, because it would tell you what class was it trying to cast to what other class, when it failed.
If your program logic requires that the handler be aware of events it shouldn't handle (why?) you could then write it like this:
private function clickHandler(event:MouseEvent):void {
var button:Button = event.currentTarget as Button;
if (button && button.enabled) // do things
}
event.target vs event.currentTarget - very-very rarely you would need the event.target, most of the time you need the currentTarget. I'm not saying it is wrong, but, it looks like it might be the problem. target is the object that was the first cause of the event. Events may bubble, which means they may travel the display list hierarchy up and down, first from the parent to child, then in reverse direction. In the example below, suppose there was a label on the button, which was clicked once the event was generated - in such case, even if you added a listener to the button, event.target would be the button label, not the button. currentTarget is, on the contrary, the immediate object which dispatched the event into the handler.
Few more things: ObjectProxy is an idiotic class, you probably shouldn't use at any event. It serves no purpose and, perhaps, buggy, but very few cared to discover its bugs so far. In a nutshell, what it does is as follows: it creates an object, which "watches" dynamic creation, assignment and removal of its properties and dispatches events when these events happen. This behavior is prone to a lot of errors and implicit bugs. For example, is foo.bar = "baz"; foo.bar = "baz"; a reassignment of the same property or not? Is foo.bar.baz = "fizzbuzz"; a modification of foo.bar? What if property name is not a sting? And so on.
Why you shouldn't use it: there is always a better way to treat your data. A more transparent, easier to debug, more efficient. This class is a prototype, which had never really worked. Besides having the behavior described above, it is huge in terms of lines of code that were used to write it. Debugging the errors that happen inside of it requires a lot of time and patience, which are certainly not worth it.
If you need an object to represent a user, define a class, with properties you expect the user to have and just use that class - this will make debugging and understanding your code much easier.
[Bindable] metadata is evil. I can't tell you you should avoid it, because it is used too often, but, I will. You should avoid it as much as possible. I didn't yet encounter an instance of when the use of this meta would be justified. Much in the similar spirit as ObjectProxy it is a prototype, something designed for lazy programmers w/o much consideration for either performance or corner cases. This is, again, a source of a lot of implicit bugs, typically difficult to spot due to the code generated around this meta "swallowing" the errors. The alternative to this meta is plain addEventListener(...) code with custom events.
Unfortunately, a lot of tutorial will use this kind of code to have you quickly started with the language + framework...
** there are some exceptions to this rule: constants are all upper-case and namespace names use underscores to separate the logical part of the word, but never use uppercase letters.
sometimes we need clone a object.but if a displayObject has some children and use the function like this:
function clone(source:*):*
{
var b:ByteArray = new ByteArray();
b.writeObject(source);
b.position = 0;
return(b.readObject());
}
but the result has no children.. .. . so what should I do ?
Unfortunately automatic cloning of objects in actionscript is a waste of time in the majority of cases.
Your snippet is right, but serialization/deserialization via ByteArray cannot perform real deep copy, i.e. copying of all references and containers.
ByteArray technique will work only with non-reference data types (Number, int, String, etc.)
So there is no silver bullet and only one adequate solution - to write the clone() method for your class manually.
I didn't have to program a clone-method myself yet, but i found a way that might do the trick. By iterating through all your variables (in an xml-representation), you can copy them in a new instance of your class.
you can find the method i am talking about on this link: http://www.learnosity.com/techblog/index.cfm/2008/2/6/AS3--Looping-over-properties-of-a-class
Let me know if it works, i'm kind of curious myself :)
For a game I'm attempting to develop, I am writing a resource pool class in order to recycle objects without calling the "new" operator. I would like to be able to specify the size of the pool, and I would like it to be strongly typed.
Because of these considerations, I think that a Vector would be my best choice. However, as Vector is a final class, I can't extend it. So, I figured I'd use composition instead of inheritance, in this case.
The problem I'm seeing is this - I want to instantiate the class with two arguments: size and class type, and I'm not sure how to pass a type as an argument.
Here's what I tried:
public final class ObjPool
{
private var objects:Vector.<*>;
public function ObjPool(poolsize:uint, type:Class)
{
objects = new Vector.<type>(poolsize); // line 15
}
}
And here's the error I receive from FlashDevelop when I try to build:
\src\ObjPool.as(15): col: 18 Error: Access of undefined property type.
Does anybody know of a way to do this? It looks like the Flash compiler doesn't like to accept variable names within the Vector bracket notation. (I tried changing constructor parameter "type" to String as a test, with no results; I also tried putting a getQualifiedClassName in there, and that didn't work either. Untyping the objects var was fruitless as well.) Additionally, I'm not even sure if type "Class" is the right way to do this - does anybody know?
Thanks!
Edit: For clarification, I am calling my class like this:
var i:ObjPool = new ObjPool(5000, int);
The intention is to specify a size and a type.
Double Edit: For anyone who stumbles upon this question looking for an answer, please research Generics in the Java programming language. As of the time of this writing, they are not implemented in Actionscript 3. Good luck.
I have been trying to do this for a while now and Dominic Tancredi's post made me think that even if you can't go :
objects = new Vector.<classType>(poolsize);
You could go something like :
public final class ObjPool
{
private var objects:Vector.<*>;
public function ObjPool(poolsize:uint, type:Class)
{
var className : String = getQualifiedClassName(type);
var vectorClass : Class = Class(getDefinitionByName("Vector.<" + className + ">"));
objects = new vectorClass(poolsize);
}
}
I tried it with both int and a custom class and it seems to be working fine. Of course you would have to check if you actually gain any speed from this since objects is a Vector.<*> and flash might be making some implicit type checks that would negate the speed up you get from using a vector.
Hope this helps
This is an interesting question (+1!), mostly because I've never tried it before. It seems like from your example it is not possible, which I do find odd, probably something to do with how the compiler works. I question why you would want to do this though. The performance benefit of a Vector over an Array is mostly the result of it being typed, however you are explicitly declaring its type as undefined, which means you've lost the performance gain. So why not just use an array instead? Just food for though.
EDIT
I can confirm this is not possible, its an open bug. See here: http://bugs.adobe.com/jira/browse/ASC-3748 Sorry for the news!
Tyler.
It is good you trying to stay away from new but:
Everything I have ever read about Vector<> in actionscript says it must be strongly typed. So
this shouldn't work.
Edit: I am saying it can't be done.
Here see if this helps.
Is it possible to define a generic type Vector in Actionsctipt 3?
Shot in the dock, but try this:
var classType:Class = getDefinitionByName(type) as Class;
...
objects = new Vector.<classType>(poolsize); // line 15
drops the mic
I don't really see the point in using a Vector.<*>. Might as well go with Array.
Anyhow, I just came up with this way of dynamically create Vectors:
public function getCopy (ofVector:Object):Object
{
var copy:Object = new ofVector.constructor;
// Do whatever you like with the vector as long as you don't need to know the type
return copy;
}