Here's a toy example distilled from a complex class:
public class MyClass {
public function MyClass() {
trace('Created');
}
public static function makeObjectAsync(callback:Function):void {
inner();
function inner():void {
var object:MyClass = new MyClass(); // line 10
callback(object);
}
}
}
After calling the static function:
MyClass.makeObjectAsync(function(object:Myclass):void { ... })
the following run-time exception occurs at line 10:
TypeError: Error #1007: Instantiation attempted on a non-constructor.
Why is this, and what can I do about it?
Edit
It appears that new (MyClass)() works. Now I'm possibly more confused.
Not too clear on the WHY to be honnest. It has to do with the scope inherited by anonymous functions, depending on how they are declared.
I have 2 solutions for you though.
If your makeObject method was not static, it would work.
Declare your anonymous function the other way :
public static function makeObjectAsync(callback:Function):void {
var inner : Function = function():void {
var object:MyClass = new MyClass();
callback(object);
};
inner();
}
You shouldn't call your variable "object". Why do you nested your inner function? Why don't you just:
public static function makeObjectAsync(callback:Function):void {
callback(new MyClass());
}
Or if you really want that nested function:
public static function makeObjectAsync(callback:Function):void {
inner();
function inner():void {
callback(new MyClass());
}
}
And you can't recall the class' constructor again, use a function which is called in the constructor then call it again. With this you aren't referencing the constructor but creating a new instance of the class.
Related
I have Flex/Java project with blazeDS. Now I have an actionscript file that call a method of another actionscript that call the remoteObject (java class who make a simple select on db)
Here's the code:
Home.as
..
private var _dm:DataManager = new DataManager;
public function getPerson():void { // this is connect to a button in .mxml
_dm.getPerson();
}
..
DataManager.as
public class DataManager {
private var _service:RemoteObject;
private var _url:URLRequest;
private var loCs:ChannelSet = new ChannelSet();
public function DataManager () {
_service = new RemoteObject("PeopleDAO");
loCs.addChannel(new AMFChannel("canale", "http://localhost:8080/FlexTRYOUT/messagebroker/amf"));
_service.channelSet = loCs;
}
private function onFault(event:FaultEvent,token:Object):void {
var _fail:String = "fault";
}
private function onResult(event:ResultEvent,token:Object):void {
per = event.result as People; // is a bean class
Alert.show(per.nome);
}
public function getPerson():void {
var token:AsyncToken = _service.getPersona();
token.addResponder(new AsyncResponder(onResult,onFault));
}
}
The call works fine, it calls java method names getPerson() of the DataManger.java class. It return simply one object with name and surname (it's just a hello world to understand this damned AsyncCall). The problem is that I don't know how send this result to Home.as with a classic (java) return type. I have the result in onResult method and I don't know how to get it.
I try to follow Brian instructions and I just waste my time. Maybe because I'm not a flex actionscript programmer but I added the code Brian posted and:
public function getPerson():void { // this is connect to a button in .mxml
_dm.addEventListener(DATA_RECEIVED, onPersonFound); * compile error 1
_dm.getPerson();
}
error is DATA_RECEIVED is undefined
than in DataManager:
public class DataManager {
public static const DATA_RECEIVED:String = "DATA_RECEIVED";
...
private function onResult(event:ResultEvent,token:Object):void {
per = event.result as People; // is a bean class
dispatchEvent(new DataReceivedEvent(DATA_RECEIVED, per)); * compile error 2
}
}
error 2 is call of possible undefined method dispatchEvent
Where is the mistake? Please guys write the complete code because I'm on flex - actionscript - blazeds from two days and I have a few time to try solution. Thanks
OK, Sorry for all this post, I just create new one (but more elaborated and clear) with the same question. Step by Step I'm studing this language and I manage to implement the Brian code but DataManager.as class must extend EventDispatcher, if I don't extend this I have the compile error I posted. At moment I mangage to obtain the resultEvent data in the method defined in the addEventListener call (onPeopleFound in this case). Thanks a lot Brian I think I surely need your help again in future (at least until acceptance of the project). Bye
You can adjust method getPerson to have two parameters referencing the callback functions.
public function getPerson(onResultCallback:Function, onFaultCallback:Function):void {
var token:AsyncToken = _service.getPersona();
token.addResponder(new AsyncResponder(onResultCallback,onFaultCallback));
}
This way you can receive data in an instance of the class you need.
One option is to dispatch an event when you get the data back from the Java call:
Home.as
...
public function getPerson():void { // this is connect to a button in .mxml
_dm.addEventListener(DATA_RECEIVED, onPersonFound);
_dm.getPerson();
}
private function onPersonFound(dataEvent:DataReceivedEvent):void {
var person:People = dataEvent.people;
//Do important processing...
}
...
In DataManager.as
public class DataManager {
public static const DATA_RECEIVED:String = "DATA_RECEIVED";
...
private function onResult(event:ResultEvent,token:Object):void {
per = event.result as People; // is a bean class
dispatchEvent(new DataReceivedEvent(DATA_RECEIVED, per));
}
}
And DataReceivedEvent.as will look like the answer to How to dispatch an event with added data - AS3
public class DataReceivedEvent extends Event
{
public static const DATA_RECEIVED:String = "DATA_RECEIVED";
// this is the object you want to pass through your event.
public var result:Object;
public function DataReceivedEvent(type:String, result:Object, bubbles:Boolean=false, cancelable:Boolean=false)
{
super(type, bubbles, cancelable);
this.result = result;
}
// always create a clone() method for events in case you want to redispatch them.
public override function clone():Event
{
return new DataReceivedEvent(type, result, bubbles, cancelable);
}
}
I know I can use the addEventListener method to handle one:
addEventListener(SFSEvent.CONNECTION, MyMethod)
as I would for handling a method in another class? Like...
addEventListener(SFSEvent.CONNECTION, Myclass.class)
or
addEventListener(SFSEvent.CONNECTION, MyClass.method)
You may pass another function handler to a class
For example
Class A {
public function A() {
addEventListener(SFSEvent.CONNECTION, MyMethod);
}
private function _handler:Function;
public function set handler(value:Function):void {
_handler = value;
}
private function MyMethod(e:SFSEvent):void {
if (_handler) {
_handler.apply(null, someParam);
}
}
}
Then pass the target handler to A instance
var a:A = new A();
var b:Myclass = new Myclass();
a.handler = b.someMethod;
If the function is a static function, You may just do it like this
addEventListener(SFSEvent.CONNECTION, SomeClass.aStaticFunction);
I am defining this function in one of my classes:
public function onUse():void {};
Then in another of my classes (let's call it "class2"), I create a object of this class, and then want to override this function with another one. After some Google-Fu, I have found this, and used it...
button.onUse {
variable = value;
}
...but it executes instantly, and not when onUse() is called - which seems to be an empty function, always.
I didn't find anything more than that - I tried a few things myself, like specifying a function inside class2 and using button.onUse = function();, but it always throws errors.
Can anyone tell me whether what I am trying to do is actually possible, and if it is, how can I do it?
You can only override functions when you are extending the class:
public class A {
public function foo():void {
doStuff();
}
}
public class B extends A {
override public function foo():void {
doOtherStuff();
}
}
var n:A = new A();
n.foo(); // => calls doStuff();
var o:B = new B();
o.foo(); // => calls doOtherStuff();
Hence, assigning a different function to a class method of an instance is not possible at runtime.
You can, however, let your original class contain a field of type Function, and then simply assign a different closure to it.
public class A {
public var foo:Function;
}
var n:A = new A();
n.foo = function ():void {
doStuff();
};
n.foo(); // => calls doStuff();
var o:A = new A();
o.foo = function ():void {
doOtherStuff();
}
o.foo(); // => calls doOtherStuff();
check the syntax of
button.onUse {
variable = value;
}
a function would be defined as
public function onUse():void {};
and overwritten with
override public function onUse():void {
}
in a different class
the way you're trying to do it, does not constitute overriding a function.
What I've done in similar circumstances is create a onClickFunction function in the class
public var onClickFunction:Function = null;
and then in the CLICK event listener function add
if(onClickFunction != null){
onClickFunction();
}
then you can assign your on-click functionality by doing something like this
button.onClickFunction = function():void{
variable = value;
// dostuff
}
this is not the best way of doing it, but probably the easiest way of implementing the functionality. And ideally you'd use inheritance the way the spacepirate suggested.
I apologize in advance if my question is not clear, because I don't know how to put this.
What I am trying to do is to reduce few lines of repeated code by implementing various OOP methods/concepts.
The problem
I have few set of of classes which has initialization process. So, I am implementing an init() method in all those classes. From the calling class (main), these objects will be instantiated and init() method of each object is called in the the order and call some other process after all of them are initialized.
Something like this
public function mainClass(){
_obj1 = new Class1();
_obj1.init();
_obj2 = new Class2();
_obj2.init();
_obj3 = new Class3();
_obj3.init();
doSomething();
}
Well, its not a big deal, but some of the classes' init() methods are asynchronous and I need to add an event listener to get notified when they have finished initialization.
I tried that by extending EventDispatcher for each of those classes and dispatch event and handle it. I even implemented a logic to handle multiple asynchhnous calls by maintaining a counter.
It will be a painful job for me whenever I need to add a new class. I thought I could untilize OOP and reduce and simplify the code.
So I came up with some thing like this, which is currently not possible (abstract class).
abstract class Initializable
{
private var _callBack:Function;
//implement initializaton process in this method
function init(callback:Function=null):void;
protected function get callback():Function{
return _callBack;
}
protected function set callback(func:Function):void{
_callBack = func;
}
protected function onComplete():void{
if (_callBack){
_callBack(this);
}
}
}
This is the main problem for me, as you know abstract class is not allowed in AS3, and the "this" refers to the Initializer class but not its subclass I guess.
This is what I am asking for your help (for the hack)
I need it very much to make my system design simple and flexible, because I can extend the solution to allow mass synchronous initialization which will allow to easily queue up all objects in the order and call init() one after the other in the order in which they are added.
The mass initializer which takes care of handling the asynchronous job
public class MassInitializer
{
private var _objList:Array; //holds objects
private var _callBacks:Array;
private var _onComplete:Function;
public function MassInitializer()
{
_objList = new Array();
}
public function add(obj:Initializable,callback:Function=null):void{
_objList.push(obj);
_callBacks.push(callback);
}
public function init():void{
for (var i:int = 0;i < _objList.length;i++){
_objList.init(this);
}
}
private function onProgress(obj:Initializable):void{
//do updates here
for (var i:int;i<_objList.length;i++){
var obj:Initializable = _objList[i];
var fun:Function = _callBacks[i];
//update progress
if (fun){
fun(obj);
}
_callBacks.splice(i,1);
_objList.splice(i, 1);
}
if (_objList.length == 0){
onComplete();
}
}
private function onComplete():void{
_onComplete(this);
}
}
the main (manager/caller) class (ClassA, ClassB are subclasses of Initialzable class)
public class MainClass
{
private var _obj1:ClassA;
private var _obj2:ClassB;
public function MainClass()
{
_obj1 = new ClassA();
_obj2 = new ClassB();
}
public function init():void{
var initManager:MassInitializer = new MassInitializer();
initManager.add(obj1);
initManager.start();
}
}
probably I am trying to (or want to )implement an observer pattern, but I don't want to confuse you by saying it in advance. Oops I said it? please ignore.
You can emulate abstract classes in ActionScript by enforcing method overrides: Just throw an error if the "abstract" method is called. I like to also implement an interface, but that's not a must, of course:
public interface Initializable
{
function init (callback : Function = null) : void;
function get callback () : Function;
function set callback ( callback : Function ) : void;
}
public class AbstractInitializableImpl implements Initializable
{
private var _callBack:Function;
protected function init(callback:Function=null):void {
throw new Error ("You must implement the init() method!");
}
protected function get callback():Function {
return _callBack;
}
protected function set callback(func:Function):void {
_callBack = func;
}
protected function onComplete():void {
if (_callBack){
_callBack(this);
}
}
}
It's not a 'hack'. It's also very simple. Make each subclass implement an interface, instead of extend an abstract class.
Here is the adobe reference on AS3 interfaces.
What I am trying to do is kind of odd, but I am wondering if anyone can come up with a clever way to do what I want to do. Basically, I want to re-define a named function at runtime. I can do this with anonymous functions, but I can't figure out a way to do it for named functions. I want to do this so that I can implement a "spy" functionality on an object for a testing framework (a port of Jasmine to Flex).
Take, for instance, this class:
public class TestClass
{
public var anonymous:Function = function():void {
trace("original anonymous");
};
public function named():void {
trace("original named");
}
}
I can easily re-define the anonymous function because it is just a variable. Javascript uses this idiom a lot.
var testClass:TestClass = new TestClass();
testClass.anonymous = function():void { trace("overridden anonymous"); }
BUT, when I do the same thing for named functions, you get a compile-time error:
// Does not compile
testClass.named = function():void { trace("overridden named"); }
I tried to make it a bit more "squishy" but this leads to a runtime failure "Cannot assign to a method named on TestClass".
// Compiles with runtime failure
testClass["named"] = function():void { trace("overridden named"); }
Can anyone more clever than I come up with a way to hack this? Can the bytecode be hijacked? Something?
I want to modify an object, not a
class
But object doesn't contain functions, only non-static variables. I tried to use prototype property and replace method there, but original method still gets called instead of injected one.
About "hack" bytecode, do you mean "hack" already loaded SWF in runtime? I think it's not possible. I'm sure, though, you can parse SWF with something like as3swf, find method in bytecode, replace it and save result in new SWF.
I had an idea bout making a function "cache" . This might work with what you need.
Let's say you have a class "Car" with a method you need to redefine at runtime:
public class Car extends Sprite
{
private var functionCache:Function;
public function Car()
{
super();
}
public function flexibleFunction(functionBody:*=null):void{
if(functionBody is Function){
functionBody.call();
functionCache=functionBody;
} else {
functionCache(functionBody);
}
}
}
Usage:
public class Main extends Sprite
{
private var car:Car;
public function Main()
{
car = new Car();
car.flexibleFunction(function(){trace("redefine test #1")});
car.flexibleFunction();
car.flexibleFunction(function(doParametersWork:String="let's see"){trace("redefine test #2: " + doParametersWork);});
car.flexibleFunction("yes they do");
car.flexibleFunction();
}
}
an easy way to accomplish what you want is to simply pass a new function to the original function and execute it from there:
package
{
//Imports
import flash.display.Sprite;
//Class
public class RedefineFunction extends Sprite
{
//Constructor
public function RedefineFunction()
{
originalFunction();
originalFunction(redefinedFunction);
}
//Original Function
public function originalFunction(redefinition:Function = null):void
{
if (redefinition != null)
redefinition();
else
trace("Original Function Definition");
}
//Redefined Function
private function redefinedFunction():void
{
trace("Redefined Function Definition")
}
}
}
traces:
Original Function Definition
Redefined Function Definition