ActionScript - Receiving Name of Calling Function or Constructor? - actionscript-3

long shot: is it possible to get the name of a calling function or the constructor from the called function? is it possible to determine the previous function of the thread?
i would like to call some setter functions from my constructor and have my setter functions determine if it was the constructor that called them.
currently, i'm setting a boolean for this functionality, but perhaps there is another way?
public function Constructor(myNumber:Number)
{
this.myNumber = myNumber;
}
public function set myNumber(value:Number):void
{
myNumberProperty = value;
//if constructor called this, return;
//else do some other stuff;
}

Quote from liveDocs:
Unlike previous versions of ActionScript, ActionScript 3.0 has no arguments.caller property. To get a reference to the function that called the current function, you must pass a reference to that function as an argument. An example of this technique can be found in the example for arguments.callee.
It was in AS2.0... It unfortunately throws an error if done in AS3.0.

Technically, you should be able to do this by generating an error and getting its stack trace. The constructor will have to be on that stack trace.
try
{
throw new Error();
}
catch (e:Error)
{
// parse this for the constructor name
trace(e.getStackTrace());
}
That would be for detecting where a function call came from...
I would still go for your solution (setting the flag), as it's more oop and probably far faster in terms of performance.

Related

AS3 : What is the context of 'this' in an anonymous function?

In this example:
public function Roulette() {
new QuickLoad(url, function (o:*):void {trace(this);});
}
when QuickLoad instance does its stuff, it calls the anonymous function. One would think that this is Roulette. But no, it turns out to be the anonymous function's caller, which is QuickLoad.
This is weird to say the least, say how am I supposed to pass the "correct" this (i.e. Roulette instance) inside the anonymous function if I don't do it the normal way?
Just save the outer this instance under a different name so that it is preserved:
public function Roulette() {
var rouletteThis = this;
new QuickLoad(url, function (o:*):void {trace(rouletteThis);});
}
There is a way to call a function with an alternate this pointer, but since your function is called from within new QuickLoad(), you need to alter that call statement, and pass your this as Roulette into the constructor. Your new QuickLoad object is unaware of its surroundings, and even the caller of the constructor is unknown to it. Thus, you need to make it aware, pass a this pointer from Roulette() to QuickLoad(), AND call the function from QuickLoad with passing an alternate this pointer.
public function QuickLoad(url:String,caller:Object=null,callback:Function=null) {
// initialization code
if (callback!=null) {
if (caller!=null) callback.apply(caller,[o]);
else callback.apply(this,[o]);
}
}
...
public function Roulette() {
new QuickLoad(url, this, function (o:*):void {trace(this);});
}
Function::apply() manual.
You can also use call() method, if your argument array has fixed length. callback.call(caller,o);
Generally, in this context, this refers to an object. To quote a rather infamous acronym: INABIAF (It's not a bug, it's a feature), LOL. So, yes, the object instance QuickLoad that is calling the function is going to be what this looks at by default.
There is an exception I know of (out of many, I'm sure)...you can get anything...variable, function, object, whatever, via this["Name of Object"]. But that's an aside.
There ARE other workarounds, I'm sure, which may or may not be practical for your purposes. This is one way of passing a function, out of many, and it's the one I use the most.
Functions do not have instances. They're not objects. If you want to send a function as an argument to another function, you simply pass it, as follows in this rather weird example.
//This function accepts a function as an argument.
function bridgeOfQuestions(person:String, response:Function):void
{
if(person == "King Arthur")
{
response("What is the average airspeed velocity of an unladen swallow?");
}
else
{
response("What is your favorite color?");
}
}
//This is the function we're going to pass.
function askQuestion(question:String):void
{
trace(question);
}
//Here, we call bridgeOfQuestions and pass it the askQuestion function.
//NOTE: Leave off the parenthesis on the function being passed!
bridgeOfQuestions("Sir Lancelot", askQuestion);
bridgeOfQuestions("King Arthur", askQuestion);
EDIT: If it is just the name you're passing, a function is a function permanently. It doesn't change, unlike an object, and as I said, it doesn't have instances. Therefore, if you merely want to print out the name of the function, you'd only use trace("Roulette").

flex4 calling a function in addEventListener with dynamic suffix

I would like to call a function name from inside an addEventListener dynamically based on function parameter.
calling with newMod("moduleA", "A"); however I am getting error TypeError: Error #1006: value is not a function.
Any suggestions on how I can call this function dynamically. I have seen some answers around using an instance[function]() but am not sure how that applies with the listener,
public function newMod(mdLd,evtTyp,param):void {
info = ModuleManager.getModule(mdLd);
var mevth:String = ("modEventHandler"+(evtTyp));
info.addEventListener(ModuleEvent.READY, function(e:ModuleEvent){
this[mevth](e, param)});
info.load(null, null, null, moduleFactory);
}
private function modEventHandlerA(e:ModuleEvent):void {
vg1.addElement(info.factory.create() as IVisualElement);
}
[EDIT]
looks like changing the call to this[mevth]() works, but I cant seem to pass additional params as needed i.e. this[mevth](parm), any suggestions welcome.
I have also updated the listener to include a function call but still no joy
When you create closure "this" doesn't point to real instance "this". You can write something like this
public function newMod(mdLd,evtTyp,param):void {
info = ModuleManager.getModule(mdLd);
var self:Object = this;
var mevth:String = ("modEventHandler"+(evtTyp));
info.addEventListener(ModuleEvent.READY, function(e:ModuleEvent){
self[mevth](e, param)});
info.load(null, null, null, moduleFactory);
}
...
But I really don't recommend you write code like this.
To awnser your comment:
Function closure means that a function remembers the context in which it has been created. In your code the following line creates a closure:
info.addEventListener(ModuleEvent.READY, function(e:ModuleEvent){
this[mevth](e, param)});
The event handler function is created in the context of the class that contains the method public function newMod(mdLd,evtTyp,param):void, so your handler has access to all members of the class. This includes variables declared in the surrounding method, the private variables/methods of the class and the protected variables/method in the whole inheritence chain of the class.
The problem with the this as Ivan Dyachenko wrote is that your handler function actually is an instance of the top-level class Function. So, if you try to call a method on this in a Function object it will be the same as calling a method in any other object - this refers to the object. In your case this will be the Function object. But your function doesn't have the method you want to call on it.
Additionally you will run into another problem with your code. Because you create the event handler inline - directly as argument of addEventListener() you will be unable to remove the event listener later. You should either use the useWeakReference parameter on addEventListener() as described here or store the handler function in a variable to hold a reference on it to remove it later with removeEventListener().

AS3 - Check if a callback function meets certain argument criteria?

If I set up a function that accepts a callback:
function loadSomething(path:String, callback:Function):void;
And that callback should accept a given type, for example a String to represent some loaded information:
function onLoaded(response:String):void;
// Load some data into onLoaded.
loadSomething("test.php", onLoaded);
Is it possible to assess the function that will be used for callback and ensure that it has both a given amount of arguments and that the argument accepts the correct type? e.g.
function broken(arg:Sprite):void;
// This should throw an error.
loadSomething("test.php", broken);
I don't think you should bother doing this kind of check as it would create an uncessary overhead. You can simply throw the exception when you do the callback:
try {
doCallback(response);
} catch(e:*) {
trace('Incompatible callback');
}
If you really want to do the check, you might be able to do it using reflection. Just call describeType(callback) from flash.utils and parse the XML.
One simple thing you can do is to check the number of acceptable arguments by calling length property on method closure like:
function some ( val1 : int, val2 : int ) : void { return; }
trace(some.length); // traces 2
Other much more complex method maybe is to use AS3Commons bytecode library. You can experiment with dynamic proxies.

AS3 Access the methods of a dynamically created movieclip

How do I access the methods of a dynamically created movieclip/object?
For simplicity sake I didn't post code on how I dynamically created the movieclip. Instead, assume its already created. It is an object. It is called field_2. Below it is referenced by using getChildByName('field_' + field.id);
Check_box_component.as
public var testVar:String = 'test';
public function testReturn()
{
return 'value returned';
}
Main.as
var temp:MovieClip = MovieClip(getChildByName('field_' + field.id));
trace(temp);
trace(temp.testReturn);
trace(temp.testVar);
Output:
[object Check_box_component]
function Function() {}
test
When I trace temp.testReturn, why does it show "function Function() {}" instead of "value returned"?
This link below helped me get this to this point.
http://curtismorley.com/2007/06/13/flash-cs3-flex-2-as3-error-1119/
have you tried:
trace(temp.testReturn());
... instead of your
trace(temp.testReturn);
... ?
I think you will have the result you are waiting for.
Actually, when doing "temp.testReturn", you are not calling the function. You need to add the parenthesis to make the actual call.
When you make a trace of temp.testReturn, the function is not executed: the trace function tell you the type of temp.testReturn, which is here correctly returned as a "function" type.
There is a difference between a function reference and a function call. Parenthesis '()' are an operator sign of ActionScript. They tell the compiler "please try to make a call to what was just behind us". Or at least I hope they are that polite.
A function in ActionScript is an object, like all other stuff. A member of Function class. You can pass it's reference back and forth, you can even call it's methods like call() or apply().
If you want a call, and not a reference, you have to use call operator.
trace(temp.testReturn());
EDIT You accepted an answer while I was typing, sorry for a duplicate answer.

Generic way to get reference to a method's caller?

I have 2 classes representing 2 objects. From the "whoCalledMe" function, I want to find out what object called the function (without passing that information in as an argument). I've used a make-believe property, "caller", that would give me the reference I'm looking for. Is there a generic way I can get a reference to the caller from there?
package {
public class ObjectCallingTheFunction {
public var IDENTITY:String = "I'm the calling function!";
public function ObjectCallingTheFunction() {
var objectWithFunction:ObjectWithFunction = new ObjectWithFunction();
objectWithFunction.whoCalledMe();
}
}
}
package {
public class ObjectWithFunction {
public function whoCalledMe ():void {
trace(caller.IDENTITY); // Outputs: "I'm the calling function!"
}
}
}
It would help to know why you need this, because I have a feeling that you don't really. If the method is anonymous, you can bind the 'this' keyword by using .apply on the method:
var foo:Function = function(arg:int):void
{
trace(this);
};
var bar:Object = {
toString: function():String { return "bar"; }
};
var baz:Object = {
toString: function():String { return "baz"; }
};
foo.apply(bar); // <-- Prints "bar"
foo.apply(baz); // <-- Prints "baz"
If the method is an instance method method however, it's a bound method and thus "this" will always point to the instance of the class it's declared in, no matter if you redefine it by using the apply method. If it's a static method, "this" doesn't make sense and the compiler will catch it.
Other than that, there's really no way short of declaring it as a parameter. There used to be a caller property on the arguments object, but it was deprecated when AS3 was released. You can get a reference to the function itself through arguments.callee, but that's not really what you asked for.
In AS3 you can throw an error and then parse the Stack Trace to find out detailed informations.
You can check here for an example:
http://www.actionscript-flash-guru.com/blog/18-parse-file-package-function-name-from-stack-trace-in-actionscript-as3
If you want to find the called function's name you can follow this example:
http://www.flashontherocks.com/2010/03/12/getting-function-name-in-actionscript-3/
I guess you want to know the caller in debug purpose. if so I would recommend setting a breakpoint in the method/function instead of tracing. When the code breaks you can backtrace the caller and a lot more. Works in Flash IDE as well as Flashbuilder. Google "as3 breakpoints" if you are new to breakpoints.
Here is the official Adobe article on using arguments.callee
http://livedocs.adobe.com/flash/9.0/ActionScriptLangRefV3/arguments.html
It includes sample code.
Hope this helps.