I'm trying to get the reserved keyword arguments array from inside a static method and I'm getting this error:
1042: The this keyword can not be used in static methods. It can only
be used in instance methods, function closures, and global code.
Here is my code:
public static function doSomething(message:String, ...Arguments):void {
var object:Object = this.arguments.caller;
}
If I take the this keyword out then I get the following error:
1120: Access of undefined property arguments.
this is reserved to reference the current instance of a class which unfortunately doesn't exist inside a static function (since static function is not tied to an instance).
You could try using the new rest keyword if you want to pass in an unknown number of arguments:
ActionScript 3.0 includes a new ...(rest) keyword that is recommended instead of the arguments class.
However if you want it just to get the caller function:
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.
public function test() {
doSomething("Hello", arguments.callee);
}
public static function doSomething(message:String, caller:Function):void {
var object:Object = caller;
}
You could get the arguments of a static method. From the documentation:
Within a function's body, you can access its arguments object by using the local arguments variable.
You do not need the this keyword, this references to the Class instance instead to the function itself:
public static function doSomething():void {
return arguments;
}
Next you can access to the arguments calling the static method:
var arguments:Object = MyClass.doSomething();
trace( arguments.callee );
But remember, like #MartinKonecny said, in AS3 is better use the ...rest keyword or pass a function reference as an argument.
The arguments object is available in static functions but is not available when using the ...rest parameter.
Use of this parameter makes the arguments object unavailable. Although
the ... (rest) parameter gives you the same functionality as the
arguments array and arguments.length property, it does not provide
functionality similar to that provided by arguments.callee. Make sure
you do not need to use arguments.callee before using the ... (rest)
parameter.
Take out the ...rest parameter and the arguments object appears.
Also, the this keyword is not always necessary.
method.apply(this, args);
may throw an error in a static function but the parameter is optional so this also works:
method.apply(null, args);
More on the rest keyword.
Related
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").
I have a Red5 service function that receives a single string as a parameter, and another function that takes no parameters, like the code below:
public class AService
{
private String someName;
public void setName(String aName)
{
someName = aName;
}
.
.
public String makeMessage()
{
return("Hello, "+someName);
}
.
.
other functions
}
I also have an ActionScript function that calls the service function, using the dynamic parameter:
public class Connector
{
private var netConn: NetConnection;
public function invokeCall(theFunc:String,...theParams): void
{
var resp:Responder = new Responder(checkResult);
netConn.call(theFunc,resp,theParams);
}
.
.
}
I am aware that the "...theParams" is actually an array of parameter objects. I also know that the NetConnector class' call() method uses that parameter object array. Unfortunately, when I do an invokeCall() on my service's makeMessage() method (without putting in a parameter) like so:
invokeCall("AService.makeMethod");
I get a function nonexistent message from Red5. The only way I can make it work is to create two invoke methods, one with parameters and one without, and call that function without parameters.
Furthermore, calling my setName() function, like so:
invokeCallwithPrams("AService.setName","factor3");
doesn't seem to work unless I change the signature of my service function:
public class AService
{
private String someName;
public void setName(String[] aName)
{
someName = aName[0];
}
.
.
public String makeMessage()
{
return("Hello, "+someName);
}
.
.
other functions
}
which I don't mind (even though the Red5 documentation indicates that I shouldn't have to treat the parameter as an array), except that when I pass the string "factor3" into the NetConnection class' call() method, somehow it becomes "[factor3]" in setName()!
Obviously, something is screwy here, but I haven't been able to figure it out.
I am using Red5 Version 1.0.1 and my Actionscript is Version 3.
Can anyone explain to me what is going on and (more importantly) how to fix this???
If so, please advise...
UPDATE: The weirdness continues
I did a test in which I changed the parameter of the function I used to set up and invoke the NetConnection class' call() method. Instead of passing it a "...theParams", I changed it to theParams:String, like so:
public function invokeCall(theFunc:String,theParams:String): void
{
var resp:Responder = new Responder(checkResult);
netConn.call(theFunc,resp,theParams);
}
Interestingly, the brackets that appear in my service method setName() go away!
Whatever this problem is, it has something to do with the dynamic parameters in Actionscript. I suspect that I have found a bug in Actionscript 3 that does not allow it to properly handle dynamic parameters that are passed to a method from another method.
Has anyone else seen this problem? Is there any solution? The dynamic parameters are supposed to allow anyone to add parameters as necessary and make them any object that is necessary. Unfortunately, it doesn't look like you can use dynamic parameters passed from another method without them being screwed up.
This looks like a serious bug in Actionscript. Am I correct?
Someone please advise...
I found the solution. It is not a bug in Actionscript, it is a bit of strangeness in the language.
The basic information about the solution can be found here:
AS3 variable length argument expand to call another function with var length args
Based on what is there, I needed to do the following in the method I am using for invokeCallwithParams:
.
.
var conn:Connector = new Connector();
private function invokeCaller(fName:String,...cParams)
{
cParams.unshift(fName);
conn.invokeCall.apply(conn,cParams);
}
This eliminates the unnecessary brackets passed into my setName() service function, meaning that I can pass dynamic, variable length parameters from one method to another...
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().
In as3 there is a flexible way to change object instance, when calling it.
call or apply members of Function object can be called with specific first arg, and reference say us, that this first arg will be "this" pointer inside function. But i've found it wrong.
I'v write little test, listed below.
public class Test
{
private var name:String = "default";
public var test3:Function = test;
public var test2:Function = function()
{
trace(this.name);
}
public function Test(name:String)
{
this.name = name;
}
public function test():void
{
trace(this.name);
}
}
and tested it.
var tmp:Test = new Test("default");
tmp.test(); //out default
tmp.test.call(new Test("new")); //out default
tmp.test2(); //out default
tmp.test2.call(new Test("new2")); //out new2
tmp.test3(); //out default
tmp.test3.call(new Test("new3")); //out default
So, in anonymous function call we can get right output, but not in case of member function.
maybe it's becouse of ambiguous "this" pointer, that should reffer real object instance for correct work, maybe smth else. I dont now, and as3 reference didnt't describe smth about it.
Finally list of questions:
Why so? By me, it's very strange, and looks like undefined behaviour;
How i can achieve that functionality? How to deceive test function like anonymous one? Isn't it call methode target?
It isn't very important, but I'll be glad any good answer. Thanks!
P.S. sorry for my English.
//EDITED: added this statement to all "name" references. Nothing changes.
When invoking the [[Call]] property, the behavior is different for
different types of closures. A closure is an object that contains a
reference to a method, and the [[Call]] property acts differently
depending on whether it is a function, method, or class closure. A
function closure is one that is of a global method that isn't
associated with any instance of a class. A method closure contains an
instance method of a class, and will always remember its original
"this" value.
If the closure is a function closure, then the first argument passed
to [[Call]] is passed on to the method and gets used as the "this"
value. If the first argument is null or undefined, then the global
object will be used as the "this" value for the method.
If the closure is a method closure, then the first argument of
[[Call]] will be ignored, and the saved "this" value for the method
closure will be passed to the method as the first argument. A method
closure records what its original "this" value was and always uses
that instead of the first argument to [[Call]].
If the closure is a class closure, and there is 1 argument passed to
[[Call]] (in addition to the "this" argument), then the call is
treated as a type conversion, and the argument will be coerced to the
type represented by the closure.
http://learn.adobe.com/wiki/display/AVM2/2.4+Method+invocation+notes
How does one get a reference the the getter and setter functions in actionscript 3?
if a method is defined on the calls, e.g.
public function blah():String { ...}
I can get a reference to it by just saying blah or this.blah
How do get a reference to
public function get blah2():String {}
public function set blah2(b:String):void {}
Thanks!
Original response:
Unfortunately, you will not be able to store references to those as functions. The getter and setter methods are actually built around the idea that you shouldn't be able to and they therefore function as a property.
Is there a reason that you need to reference the functions specifically?
The comment I'm responding to:
I want to dynamically add external interface methods based on custom metadata tags, e.g. [External]. I was able to do this for the regular methods, but I'm trying to extend this to getter/setters as well. To do this, I need to get a reference to the function dynamically, so I can execute it with the right args using the apply function.
I think you're better off using a multi-step approach in that case. Since getters and setters function as a property and not a method, it would make sense to test to see if it is a property and then simply assign it a value directly. Would you be able to use this:
if( foo.blah2 is Function )
{
foo.blah2.apply( foo, arr );
}
else
{
foo.blah2 = arr[ 0 ];
}