This is my code:
public function setPaneContent(names : Array, parent : AbstractPane) : void {
//....
okButton.addEventListener(MouseEvent.CLICK, function okMouseClickHandler(e : Event) : void {
parent.addNewPane(valuesPane, parent);
PopUpManager.removePopUp(/*need to put "this"*/);
});
//.....
}
When i call PopUpManager.removePopUp(/*need to put "this"*/);, i need to make a reference at the object that contains this method(this).
So my question is: "Is it possible to make a reference at 'this' keyword within an anonymous method?"
store this to some variable: _this = this in the constructor, use _this. (it works in javascript)
You don't have to, you can call another function
public function setPaneContent(names : Array, parent : AbstractPane) : void
{
okButton.addEventListener(MouseEvent.CLICK,
function okMouseClickHandler(e : Event) :void
{
parent.addNewPane(valuesPane, parent);
// call the remove function where you can reference "this"
remove();
});
//.....
}
private function remove():void
{
PopUpManager.removePopUp(this);
}
Related
With D, how can I pass a function (possibly reference to a function) as an argument to be executed inside other function?
import std.stdio : writeln;
class Event {}
class EventTarget
{
void addEventListener(string eventName, void delegate(Event event) callback)
{
// TODO: add to slice to execute later, for now execute directly
callback();
}
}
void main()
{
auto variableFromParentScope = "lorem ipsum";
auto target = new EventTarget();
target.addEventListener("load", (Event event) => { writeln(variableFromParentScope, event); }, true);
}
Gives me the error:
onlineapp.d(10): Error: delegate callback(Event event) is not callable using argument types ()
onlineapp.d(10): missing argument for parameter #1: Event event
onlineapp.d(18): Error: function onlineapp.EventTarget.addEventListener(string eventName, void delegate(Event event) callback) is not callable using argument types (string, void delegate() #system delegate(Event event) pure nothrow #safe, bool)
onlineapp.d(18): cannot pass argument __lambda1 of type void delegate() #system delegate(Event event) pure nothrow #safe to parameter void delegate(Event event) callback
I have set up the example here: https://run.dlang.io/is/FnQoId
SOLUTION, With the help from the answers I fixed it like this:
import std.stdio : writeln;
class Event {}
class EventTarget
{
void addEventListener(string eventName, void delegate(Event event) callback)
{
// TODO: add to slice to execute later, for now execute directly
callback(new Event());
}
}
void main()
{
auto variableFromParentScope = "lorem ipsum";
auto target = new EventTarget();
target.addEventListener(
"load",
(Event event) {
writeln(variableFromParentScope, event);
}
);
}
Working example: https://run.dlang.io/is/6aDRoU
You are using the wrong syntax for the delegate, as you can also see in the error message it doesn't have the expected type.
To explain further, I will show you how it changes if you extend it to the longer form of a delegate instead of using the shorthand =>:
(Event event) => { writeln(variableFromParentScope, event); }
becomes
(Event event) { return { writeln(variableFromParentScope, event); }; }
As you can see you are returning a delegate with no parameters inside your actual delegate. If you remove the =>, your delegate will work as expected.
Alternative valid forms for your delegate parameter would be:
(event) { ... }
delegate (Event event) { ... }
delegate (event) { ... }
&someMemberMethod // some object member method taking in Event as first parameter
toDelegate(&someGlobalFunction) // from std.functional
Only if you want to return something you use the => arrow. A use-case for () => { something } would be a delegate returning a delegate (like a delegate generating delegates for a given input)
But also wrong in your question is that you are calling that function with a , true in the calling parameters, which makes the error message very confused, and that you aren't passing an event parameter to the callback, which would be another error in the code snippet.
target.addEventListener("load", (Event event) => { writeln(variableFromParentScope, event); }, true);
(Args) => {} is a lambda which returns a lambda.
Correct forms:
target.addEventListener("load", (Event event) { writeln(variableFromParentScope, event); }, true);
target.addEventListener("load", (Event event) => writeln(variableFromParentScope, event), true);
While experimenting with a basic coding stuff, I wondered, if a value returned by a method called by a delegate, could be used or captured. In other words, where will the return value will go ?
For example :
class Main extends Sprite
{
public var mc:MyMc;
function Main()
{
mc.addEventListener( "myClick" , myClick);
}
function myClick(e:Event):String //returning a string
{
return "What happens to this return value ???"
}
}
class MyMc extends MovieClip
{
function MyMc()
{
addEventListener( MouseEvent.CLICK , onClick);
}
function onClick(e:Event):String //returning a string
{
dispatchEvent(new Event("myClick"));
}
}
As I know it's not possible to do, but, there are at least some ways to implement the logic similar to what you've told about.
For example, you may call a method of a dispatcher, from a listener method:
class Main extends Sprite
{
public var mc:MyMc;
function Main()
{
mc.addEventListener("myClick" , myClick);
}
function myClick(e:Event):void
{
mc.specialMethod("some string");
}
}
class MyMc extends MovieClip
{
function MyMc()
{
addEventListener(MouseEvent.CLICK , onClick);
}
function onClick(e:Event):void
{
dispatchEvent(new Event("myClick"));
}
public function specialMethod(param:String):void
{
// Do something to the param
}
}
Also, you may think about dispatching an event from the Main class, and listen to it in the MyMc class, or pass a callback, which returns a string, from Main to the MyMc.
It's according to you and your needs to return something from the listener function because normally it must return nothing :
... This function must accept an Event object as its only parameter and must return nothing, ...
but you can of course get the returned value(s), take a look on this little example :
var light_on:Boolean = false;
btn_light_on.addEventListener(MouseEvent.CLICK, btn_on_onPress);
btn_light_off.addEventListener(MouseEvent.CLICK, btn_off_onPress);
function btn_on_onPress(e:MouseEvent): Boolean {
light_on = true;
if(e.target === btn_light_off){
light_on = false;
}
return light_on;
}
function btn_off_onPress(e:MouseEvent): void {
trace('The light is', btn_on_onPress(e) ? 'on' : 'off');
}
Hope that can help.
I have this situation where I declare inside my main class a function that looks like this:
public class Main extends MovieClip
{
public static var instance:Main;
public function Main()
{
// constructor code
welcomeScreen();
instance = this;
}
public final function welcomeScreen():void
{
//some code in here
}
public final function startLevelOne():void
{
//some other code here
}
}
In some other class I use this statement to fire a reset:
restart.addEventListener('click', function() {
Main.instance.welcomeScreen();
});
Somehow in another class I try to use the same statement for 'startLevelOne' but it seems it is not working and gives the fallowing error:
1195: Attempted access of inaccessible method startLevelOne through a reference with static type Main.
Any ideas?
UPDATE #1
The class where I try to access the function is in full this one:
public class LevelBrief extends MovieClip
{
public function LevelBrief()
{
// constructor code
startBut.addEventListener('click', function() {
Main.instance.startLevelOne();
});
}
}
UPDATE #2
I have pasted the full code of the main definition here http://pastebin.com/s6hGv7sT
Also the other class could be found here http://pastebin.com/s6h3Pwbp
UPDATE #3
Even though the problem was solved with a workaround, I still cannot understand where was the problem.
I would recommend to leave the static instance (singleton), and work event-based. Now you make all functions public, which is not desirable. It's not that hard to use custom events. See this is how your Main class could look:
public class Main extends MovieClip
{
public function Main()
{
this.addEventListener(Event.ADDED_TO_STAGE, handleAddedToStage);
}
public function handleAddedToStage(event:Event)
{
this.removeEventListener(Event.ADDED_TO_STAGE, handleAddedToStage);
this.showWelcomeScreen();
stage.addEventListener(ScreenEvent.SHOW_WELCOME_SCREEN, handleScreenEvent);
stage.addEventListener(ScreenEvent.SHOW_LEVEL, handleScreenEvent);
}
private function handleScreenEvent(event:ScreenEvent):void
{
switch (event.type)
{
case ScreenEvent.SHOW_WELCOME_SCREEN:
{
this.showWelcomeScreen()
break;
}
case ScreenEvent.SHOW_LEVEL:
{
// event.data contains level number
this.startLevel(event.data);
break;
}
default:
{
trace("Main.handleScreenEvent :: Cannot find event.type '" + event.type + "'.");
break;
}
}
}
private function showWelcomeScreen():void
{
trace("show WelcomeScreen")
//some private code in here
}
private function startLevel(level:int):void
{
trace("start level: " + level)
//some other private code here
}
}
This is how the custom event class should look (ScreenEvent.as). Note it has an optional parameter called data. You can pass any value (objects, numbers, strings etc) into this. To the example as clear as possible, I used one event-class for both actions, you can also choose to make more specific custom events for other actions with more detailed parameters, you would have names like ScreenEvent, LevelEvent, PlayerEvent, GameEvent etc etc..
At the top of the class the (static constant) types are defined. An event should only have getters.
package
{
import flash.events.Event;
public class ScreenEvent extends Event
{
public static const SHOW_WELCOME_SCREEN:String = "ScreenEvent.showWelcomeScreen";
// event.data contains level number
public static const SHOW_LEVEL:String = "ScreenEvent.showLevel";
private var _data:String;
public function ScreenEvent(type:String, data:String):void
{
super(type);
this._data = data;
}
public function get data():String
{
return this._data;
}
override public function clone():Event
{
return new ScreenEvent(this.type, this._data);
}
}
}
.. Anywhere in your code you can dispatch the event to the stage.
// dispatch event to Main (stage). Should show welcome screen in our case
stage.dispatchEvent(new ScreenEvent(ScreenEvent.SHOW_WELCOME_SCREEN));
// show level 2
stage.dispatchEvent(new ScreenEvent(ScreenEvent.SHOW_LEVEL, 2));
I know, its a bit more code, it looks more difficult at first but if the project grows, it will help a lot. The difference with events is 'this could happen, and when it happens, do this' instead of 'do this here, do that over there'
The advantage is that if you remove the event listener in the Main class, nothing will break (loosely coupled). This makes it easier to maintain, it saves a singleton, and you have the ability to extend the Main class if you want to.
I think you wrote
Main.startLevelOne();
instead of
Main.instance.startLevelOne();
Hmm. Given your code, there is only one serious question - what is PerwollGame? You have there public static var instance:PerwollGame; and you assign it an object of type Main. Perhaps that PerwollGame has a startLevelOne() function with a different signature, that obscures your function in the Main class. Also, the other people who answered you are right as well, you should never use nested functions in your code, really put that listener of yours out from inline declaration.
Judging from your coding style and the error reported, I would assume you did this.
public static function startLevelOne():void
There is a fine line between static methods and instantiated objects.
Also never use nested functions
public class LevelBrief extends MovieClip
{
public function LevelBrief()
{
// constructor code
startBut.addEventListener('click', onMyClick )
}
public functiononMyClick (e:Event) {
Main.instance.startLevelOne();
});
}
}
I assume that when you register the listener Main.instance is not already assigned.
Did you try to trace Main instance here?
public function LevelBrief()
{
// constructor code
startBut.addEventListener('click', function() {
Main.instance.startLevelOne();
});
trace(Main.instance); // I assume Main.instance is null
}
what about if you add the listener in another method in LevelBrief like :
public function registerListeners():void{
trace("Main.instance == null? -> " + (Main.instance == null)); //not null here if called later.
startBut.addEventListener('click', function() {
Main.instance.startLevelOne();
});
}
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.
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.