Clearing eventListeners on a FileReference object - actionscript-3

I have a strange issue! I am trying to remove an event listener on a FileReference object by calling a function, but it seems not to be removed, and I do not understand why.
Here is the code:
private function clearFileUploadListeners(file:FileReference, index:String):void {
var dispatchEvent:Function = function(event:Event):void {
dispatch(event.type, event, index);
};
file.removeEventListener(Event.COMPLETE, dispatchEvent);
var bool:Boolean = file.hasEventListener(Event.COMPLETE);
if (bool)
trace("ERROR");
}
When I run this code, the trace actually happens. I don't understand why this boolean returns true, when I just tried to remove the eventListener just above! I guess I am probably doing something really stupid because it seems like a strange error.
I hope someone can please help me on this issue.
EDIT:
I believe it has to do with the fact that the dispatchEvent function is defined inside another function when I add the listener:
private function upload(file:FileReference, index:String):void {
var dispatchEvent:Function = function(event:Event):void {
dispatch(event.type, event, index);
};
file.addEventListener(Event.COMPLETE, dispatchEvent);
}
The problem is that I need to access this "index" variable from the listener, and I can't set it as a global variable as each file has it's own index and it's a burden if I have to extend each event class to keep track of the index (Event, ProgressEvent, ..). I hope someone can please help me on this.
EDIT2:
I actually found a temporary solution, I am not sure if it is the best! I put my removeListener method actually inside the upload method, but made it a variable. As AS3 allows dynamic object, I attached this method to one of my object, and so I just call the reference to the method when necessary. The event is actually removed. Is this a good solution please?
Thank you very much,
Rudy

You're right, it has to do with the fact that you're defining a function inside another function, then using it to handle events.
Each time the function upload is called, it creates a new closure, and assigns a reference to it to the dispatchEvent variable, which is then passed to the addEventListener class. So each time upload is called, it is using a new, different closure in the call to addEventListener. Similarly, in the clearFileUploadListeners function, a new closure is being created on each call (which happens to have the same code each time, but isn't the same function object). The call to removeEventListener does nothing if the given callback has not been added as an event listener for the given event, which is the case here.
To solve your problem, you need to store a reference to the closure that you pass to the addEventListener function. This way, you can get a reference to the same closure that was added when you need to remove it later in clearFileUploadListeners.
You can try something along the lines of the following code (untested):
import flash.utils.Dictionary;
var callbackRegistry:* = new Dictionary();
private function upload(file:FileReference, index:String):void {
var dispatchEvent:Function = generateFileUploadCompleteCallback();
callbackRegistry[file] = dispatchEvent;
file.addEventListener(Event.COMPLETE, dispatchEvent);
}
private function clearFileUploadListeners(file:FileReference, index:String):void {
var dispatchEvent:Function = callbackRegistry[file];
callbackRegistry[file] = null;
file.removeEventListener(Event.COMPLETE, dispatchEvent);
var bool:Boolean = file.hasEventListener(Event.COMPLETE);
if (bool)
trace("ERROR");
else
trace("YAY, ALL OK!");
}
private function generateFileUploadCompleteCallback(index:String):Function {
return function(event:Event):void {
dispatch(event.type, event, index);
};
}

Two other things to note on this subject.
If you must utilize a native Event directly then you should pretty much always make sure and use these last three optional params :
myObject.addEventListener( Event.COMPLETE, myFunction, false, 0, true );
Check Grant Skinner's post on the subject here :
http://gskinner.com/blog/archives/2006/07/as3_weakly_refe.html
And the very best practice of all is to ALWAYS (seriously always) use Robert Penner's Signals (instead of custom events) and his NativeSignals (to wrap needed native Flash events).
Five times faster than Flash's native events.
Always safe with weak references.
Any number of typed payload(s) in each Signal.
Get the SWC here :
https://github.com/robertpenner/as3-signals
Signals were designed to solve the very problem you are having.
Imagine instead of creating an array and managing that to remove all listeners if you could just call :
signalBtnClicked.removeAll();
or
signalBtnClicked.addOnce( function( e : MouseEvent ) : void { /* do stuff */ } );
Knowing that the closure you just created will immediately be dereferenced once it is called and happily go night night when the GC makes its rounds.

Related

AS3: Returning value from another function after event happened

Basically I want to check if a user exists in a database using AMF (and that works great!). But then I want to return the boolean value to another function (in another class) that originally called the "checkUserExistance" function. But, since the database connection isn't immidiate, this function will always return a false value (even if "result" is true). So I would like to have the return-line inside the "onUserChecked"-function but that of course gives me an error. I thought I could create an eventListener, but then, the "return userExists"-line would also have to be inside another function, which doesnät work(?)... What can I do?
public function checkUserExistance(username:String) {
var responderBOOLEAN:Responder = new Responder(onUserChecked, onFault)
var userExists:Boolean = false;
connection.connect(gateway);
connection.call("User.checkUser", responderBOOLEAN, username);
connection.close();
function onUserChecked(result:Boolean):void {
userExists = result;
}
return userExists;
}
I'm sorry but you are trying to force an Asynchronous call to a Synchronous one and this is WRONG.
See here
You should learn how to handle events in the correct way.
What can i suggest you that helped me a lot is this
The only true answer here is to save userExists as a member variable, and dispatch event when the server returns you a response. The client side of the things should be similar to:
// add listener, ServerEvent is a custom event (see below)
server.addEventListener(ServerEvent.CHECK_RESPONSE, onCheckResponse);
server.checkUserExistance('username'); // start the query
function onCheckResponse(e:ServerEvent):void {
if (e.userExists) {
}
}
// inside server class
function onUserChecked(result:Boolean):void {
userExists = true;
dispatchEvent(new ServerEvent(ServerEvent.CHECK_RESPONSE, userExists));
}
/* ServerEvent is a custom class that extens Event
Such classes are used so you can pass special properties in them
via constructor (pass data, store it into member variable)
and through getter for that variable.
If you don't like it, simply add/dispatch Event.COMPLETE
and use public property to get userExists from server
*/

closures with popups using flex 4.6

I have this custom event handler that shows a popup and accepts input from the user:
private var mySkinnablePopupContainer:MySkinnablePopupContainer;
private function handleShowGridPopupEvent(event:ShowGridPopupEvent):void {
var mouseDownOutSideHandler:Function = function(mdEvent:FlexMouseEvent):void {
// At this point, event.targetControl contains the wrong object (usually the previous targetControl)
if (mdEvent.relatedObject != event.targetControl) {
mySkinnablePopupContainer.close();
}
}
var gridPopupSelectionHandler:Function = function(popEvent:PopUpEvent):void {
if (!popEvent.commit) return;
// At this point, event.targetData contains the wrong object (usually the previous targetData)
myModel.doSomethingWithData(popEvent.data.selectedItem, event.targetData);
}
if (!mySkinnablePopupContainer) {
mySkinnablePopupContainer = new MySkinnablePopupContainer();
mySkinnablePopupContainer.addEventListener(PopUpEvent.CLOSE, gridPopupSelectionHandler);
mySkinnablePopupContainer.addEventListener(FlexMouseEvent.MOUSE_DOWN_OUTSIDE, mouseDownOutSideHandler);
}
// At this point, event.targetData contains the correct object
mySkinnablePopupContainer.dataProvider = getMyDPArrayCollection(event.targetData);
mySkinnablePopupContainer.open(this);
var point:Point = event.targetControl.localToGlobal(new Point());
mySkinnablePopupContainer.x = point.x + event.targetControl.width - mySkinnablePopupContainer.width;
mySkinnablePopupContainer.y = point.y + event.targetControl.height;
}
Every time the function handler gets called, it will have the correct ShowGridPopupEvent object but by the time it calls the
gridPopupSelectionHandler, it will contain the old object from a previous call. It works the first time, subsequent calls fails.
Somehow the reference to the event object changed somewhere in between before opening the popup and after.
Any idea what am I doing wrong here? Is this a bug with flex?
found the prob. since im attaching listener only once, it will reference the old listener, with the reference to the old data. i guess i was expecting its reference to be updated whenever i create the closure. not in this case. possible fix is to remove the listener and re-add it again but I abandoned the idea of using closures, and aside from what RIAStar mentioned, it is also impractical as it only gives more overhead by creating a new function for every invocation of the handler.

in AS3, removeEventListener(Event.ENTER_FRAME) is not working

I have been dealing with this problem for days already. I am at my wits' end!
I can't seem to find a definitive answer anywhere on any of the forums, documentation, etc.
Everything looks fine at first run, or when I load a next level for the user to play. But if the user hits the ESC key to load a different level, the ENTER FRAME listener does not get removed and it duplicates all the triggers in it, showing the player going really fast, and all funky, because it builds on top of the previously instantiated ENTER FRAME listener.
I don't know if I have a problem of an anonymous function, or an unknown instance being referenced in my removeEvent... command... Bottom line, I give up and I need this working HELP!!!
Here's the code:
function initPlay():void
{
//code here determining what display object to add to the list and assign it to the currentLevel variable (a movieclip)
if(userIsLoadingOtherLevel){
removeEnterFrameListener();
addChild(currentLevel);
}
if(userIsGointToNextLevel)
addChild(currentLevel);
currentLevel.addEventListener(Event.ENTER_FRAME, onEnterFrame);
function onEnterFrame(event:Event):void
{
//collision detection, parallax scrolling, etc, etc is done here.
if(allCoinsCollected)
loadNextLevel();
if(ESCKeyPressed)
ESCKeyPressHandler();
}
function loadNextLevel():void
{
removeChild(currentLevel);
newLevelToLoad++
removeEnterFrameListener();
initPlay();
}
function ESCKeyPressHandler():void
{
removeChild(currentLevel);
initPlay();
}
function removeEnterFrameListener();
{
currentLevel.removeEventListener(Event.ENTER_FRAME,onEnterFrame)
trace("currentLevel.hasEventListener(Event.ENTER_FRAME) = "+currentLevel.hasEventListener(Event.ENTER_FRAME)); //outputs TRUE if called from loadNextLevel but FALSE if called from initPlay() !!!
}
}
I also tried to add and remove the eventListener to stage, MovieClip(Root), or nothing at all and the result is always the same.
I know that there may be other ways to design such a process, but please note I am not really flexible at the moment on doing this because the project is very long (about 4000 lines of code) and removing the ENTER FRAME this way, crazy or not should still work!!
THANK YOU in advance for anyone willing to help.
The problem appears to be the nested functions inside the initPlay() method.
Each time you call initPlay() you are defining new functions. Some of these nested functions call initPlay() themselves.
Functions are objects (memory references). So each time you call initPlay() you are making new references to new functions. So when you try to remove an event listener, you're only able to remove one of these event handlers (the one in the current scope of execution).
I'm not sure if I'm explaining this clearly, perhaps this example will help. I'll use numbers to represent the references to each function, and a simple scenario that is similar to yours:
function example():void
{
addEventListener(MouseEvent.CLICK, mouseClickHandler);
function mouseClickHandler(event:Event):void
{
if (someCondition)
{
example();
}
else
{
removeEventListener(MouseEvent.CLICK, mouseClickHandler);
}
}
}
When we run this function the first time, a new function is defined within the scope of the example() function. Lets use the number 1 to represent the reference to this nested function. someCondition is true on the first time around, and so the example() function is called again.
On the second execution of the example() function, a new reference to the mouse event handler is created (#2). We also add the event listener again. At this point, there are two event handling functions in memory, and both will be executed when the event is dispatched.
Let's say that in the second invocation of example() that someCondition is false and now we want to remove the listener. When we call:
removeEventListener(MouseEvent.CLICK, mouseClickHandler);
It's referring to event handler #2. Event handler #1 still exists, and because it's hidden in the scope of the first invocation of example() it can't be removed here.
My simple example breaks down after this... but I hope it makes it clear why your event handlers shouldn't be nested inside a function. Admittedly, this is difficult to describe and even more so in a real world example like yours. But I'm pretty confident that this is the source of most, if not all, of the issues you describe.
Here's how I was able to get around this without changing the scope of the nested functions (although I agree that would be the preferred solution) by creating a boolean variable called "loadingNewGame" and changing it to true from outside the onEnterFrame (in fact, this assignment was done from initPlay() and then from onEnterframe I called removeEnterFrameListener() function. This did the trick.
here's the code in case anybody is interested:
// package, and other code here.
var loadingNewGame:Boolean = new Boolean(false);
function initPlay():void
{
//code here determining what display object to add to the list and assign
//it to the currentLevel variable (a movieclip)
if(userIsLoadingOtherLevel)
{
loadingNewGame = true;
removeEnterFrameListener();
addChild(currentLevel);
}
if(userIsGointToNextLevel)
addChild(currentLevel);
loadingNewGame:Boolean = false;
currentLevel.addEventListener(Event.ENTER_FRAME, onEnterFrame);
function onEnterFrame(event:Event):void
{
if(loadingNewGame)
removeChild(currentLevel);
//collision detection, parallax scrolling, etc, etc is done here.
if(allCoinsCollected)
loadNextLevel();
if(ESCKeyPressed)
ESCKeyPressHandler();
}
function loadNextLevel():void
{
removeChild(currentLevel);
newLevelToLoad++
removeEnterFrameListener();
initPlay();
}
function ESCKeyPressHandler():void
{
initPlay();
}
function removeEnterFrameListener();
{
currentLevel.removeEventListener(Event.ENTER_FRAME,onEnterFrame)
trace("currentLevel.hasEventListener(Event.ENTER_FRAME) = "+currentLevel.hasEventListener(Event.ENTER_FRAME));
//outputs true
}

Calling certain functions whitout having the right arguments

I have two function on my AS3 program, one fires when the width and height changes:
stage.addEventListener(Event.RESIZE, resizeListener);
function resizeListener (e:Event):void {
//some commands
}
And the second one fires one a number of milliseconds pass:
var myTimer:Timer = new Timer(clockUpdate, 0);
myTimer.addEventListener(TimerEvent.TIMER, updateData);
myTimer.start();
function updateData(e:TimerEvent):void {
trace("AUTOUPDATE");
trace(e);
}
I need to fires those function also manually, lets say when the user press a button, but i don't know what parameters i have to send them when they are called manually.
I tried just resizeListener() and updateData() but of course it fails asking me for the parameter.
You can make parameters in a function optional by providing a default value. This is an example by taking your two functions above and making the event parameters optional:
function resizeListener(e:Event = null):void {
//some commands
}
and
function updateData(e:TimerEvent = null):void {
trace("AUTOUPDATE");
trace(e);
}
Calling, for example, resizeListener() will now execute the function and the value of e will default to null.
Making the Event parameter optional, resizeListener(e:Event=null), as in walkietokyo's answer, is a perfectly valid and often convenient solution. Another alternative is to put the stuff you want to be able to do without the event being triggered in a separate function, that can be called by the event handler and from anywhere else.
So assuming for example that what you want to do on resize is to rearrange the layout, and you also want to do that same layout setup at initialization, or at the click of a button, or anytime really, you could do something like this:
stage.addEventListener(Event.RESIZE, resizeListener);
function resizeListener(e:Event):void {
rearrangeLayout();
}
function rearrangeLayout():void {
// The actual rearrangement goes here, instead of in resizeListener. This can be called from anywhere.
}
Which way to do it is probably a matter of taste or can vary from case to case, really, both works fine.
A benefit of separating things in an event handler and another function is that there will not arise a situation where you would have to check if the e:Event parameter is null or not. In other words, you would have code that is dependent on the Event, if any, in the event handler, and code that is independent of the Event in a more general function (not an event handler).
So in a more general and schematic case, the structure would be something like this:
addEventListener(Event.SOME_EVENT, eventListener);
function eventListener(e:Event):void {
// Code that needs the Event parameter goes here (if any).
// Call other function(s), for the stuff that needs to be done when the event happens.
otherFunction();
}
function otherFunction():void {
// Stuff that is not dependent on the Event object goes here, an can be called from anywhere.
}

remove ENTER_FRAME EventListener from inside this as3

This is my code in Flash/AS3, in main class.
addEventListener(Event.ENTER_FRAME,function(e:Event){
if(findObject == true){
// I want to remove this ENTER FRAME
}
});
try this:
e.currentTarget.removeEventListener(e.type, arguments.callee)
You shouldn't be doing what you do in the code above.
The mgraph's code has a tiny chance of failing to work as advertised if the currentTarget of the event doesn't have a removeEventListener() method (possible, but very unlikely). From the compiler standpoint though you will be trying to dynamically resolve the method on a generic object which is error prone and should be handled with care. This is hazardous because it shows that the programmer "did not know" what kind of object was she expecting to handle and worked by assumption. Assumptions are great for finding a solution but are equally bad for implementing one.
If you thought of optimizing something in the way you did it, then, just FYI this actually creates a unique (redundant) name in the symbol table (in the compiled SWF file) which causes worse compression of the SWF.
If you are doing this as a matter of experiment, this is fine, but you should avoid such code in real life projects.
One more thing to be aware of: comparison to true constant is 100% useless. If such comparison makes any sense at all (i.e. findObject may evaluate to false any time), then if (findObject) { ... } is equivalent but shorter version of your code.
Last thing, hopefully, the anonymous function is missing return type declaration. It won't really change much in your example, except that you will get compiler warning. Omitting type declaration is, in general, a bad style.
EDIT
public function addEventListener(type:String, listener:Function ...):void
{
this._listeners[type].push(listener);
}
public function dispatchEvent(event:Event):void
{
for each (var listener:Function in this._listeners[event.type])
listener(event);
}
public function removeEventListener(type:String, listener:Function, ...):void
{
delete this._listeners[type][listener];
}
Suppose you actually want to implement IEventDispatcher (instead of using another EventDispatcher - you may have your reasons to do so, one such reason is that native EventDispatcher generates insane amounts of short-lived objects - events, and you may want to reduce that.) But there is no way you can replicate event.target or event.currentTurget in your code because you can't access the object owning the method, so, you would leave that out.
Another example:
public class SomeEvent extends Event
{
private var _target:NotEventDispatcher;
public function SomeEvent(type:String, someTarget:NotEventDispatcher)
{
super(type);
this._target = someTarget;
}
public override function get target():Object
{
return this._target;
}
}
This is something that I actually saw in real world, this was used in either Mate or similar framework to sort of "anonymously" connect all event dispatchers to a single static instance of some "mothership event dispatcher".
I don't necessarily justify this approach, but, technically, nothing stops you from doing either one of these. What I was saying in my post above is that in certain situations the language promises you things, like, if you did:
var dispatcher:IEventDispatcher;
try
{
dispatcher = IEventDispatcher(event.currentTarget);
// now you can be sure this object has removeEventListener
dispatcher.removeEventListener(event.type, arguments.callee);
}
catch (error:Error)
{
// but what are you going to do here?
}
But the most common case would be you subscribing to a bubbling event, in which case, you don't know whether you want to unsubscribe from event.target or event.currentTtarget - because you don't know which one is that you are listening to.
I agree with wvxvw.
Another way to approach your problem is to have a variable to control the "state" of your ENTER_FRAME event:
private var _state:String;
private function init(e:Event):void {
addEventListener(Event.ENTER_FRAME, loop, false, 0, true);
}
private function loop(e:Event):void {
switch(_state) {
case "play":
// do play stuff
// when you want to pause
// goToPause();
break;
}
}
// you can call the method below from a button or whatever you want
private function goToPause():void {
_state = "pause";
// do some stuff here
// when you are done, switch "_state" back to "play"
}
In this example, you keep listening for ENTER_FRAME, but it only does things when the _state variable is set to "play". You can also remove the event listener in the goToPause method:
private function goToPause():void {
_state = "pause";
removeEventListener(Event.ENTER_FRAME, loop);
}
However, the nice thing about using the "_state" to switch things is that you don't end up having a mess of addEventListeners and removeEventListeners (which is what can happen depending on how complicated your loop gets) that you have to keep track of.
You should not use anonymous function call if you would like to remove listener some time later.
public function main():void
{
//...
//some method, where you add event listener
//...
//adding enterFrame event listener
this.addEventListener(Event.ENTER_FRAME,enterFrameHandler);
//...
}
private function enterFrameHandler(e:Event)
{
if(findObject) // " == true" is not really necessary here.
{
// removing enterFrame listener:
this.removeEventlistener(Event.ENTER_FRAME,enterFrameHandler);
}
}
Just for a completeness with the other techniques mentioned here, the function you are creating is a unbound closure, so you can also leverage that concept to reference both your function and dispatcher.
var callback:Function;
var dispacher:IEventDispatcher = this;
addEventListener(Event.ENTER_FRAME, callback = function(e:Event){
if(findObject == true){
dispacher.removeEventListener(Event.ENTER_FRAME, callback);
}
});
Normal closed-over variable rules apply.