So if I'm making a boolean variable saying from one class. And setting it to true;
class 1
yes = true;
And the boolean variable goes from class 1 to class 2, and then class 2 applies the action.
class 2
if (yes)
{
do this
}
How do I do this? Can you give me a formula? Thanks.
Provided a is a variable of type Class1, it is instantiated and it is accessible in Class2 simple
if (a.yes) { do_this(); }
should do the trick.
Related
I'd like to use ES6 public class fields:
class Superclass {
constructor() {
// would like to write modular code that applies to all
// subclasses here, or similarly somewhere in Superclass
this.example++; // does NOT WORK (not intialized)
//e.g. doStuffWith(this.fieldTemplates)
}
}
class Subclass extends Superclass {
example = 0
static fieldTemplates = [
Foo,
function() {this.example++},
etc
]
}
Problem:
ES6 public fields are NOT initialized before the constructors, only before the current constructor. For example, when calling super(), any child field will not yet have been defined, like this.example will not yet exist. Static fields will have already been defined. So for example if one were to execute the code function(){this.example++} with .bind as appropriate, called from the superclass constructor, it would fail.
Workaround:
One workaround would be to put all initialization logic after all ES6 public classes have been properly initialized. For example:
class Subclass extends Superclass {
example = 0
lateConstructor = (function(){
this.example++; // works fine
}).bind(this)()
}
What's the solution?
However, this would involve rewriting every single class. I would like something like this by just defining it in the Superclass.constructor, something magic like Object.defineProperty(this, 'lateConstructor', {some magic}) (Object.defineProperty is allegedly internally how es6 static fields are defined, but I see no such explanation how to achieve this programatically in say the mozilla docs; after using Object.getOwnPropertyDescriptor to inspect my above immediately-.binded-and-evaluated cludge I'm inclined to believe there is no way to define a property descriptor as a thunk; the definition is probably executed after returning from super(), that is probably immediately evaluated and assigned to the class like let exampleValue = eval(...); Object.defineProperty(..{value:exampleValue})). Alternatively I could do something horrible like do setTimeout(this.lateConstructor,0) in the Superclass.constructor but that would break many things and not compose well.
I could perhaps try to just use a hierarchy of Objects everywhere instead, but is there some way to implement some global logic for all subclasses in the parent class? Besides making everything lazy with getters? Thanks for any insight.
References:
Run additional action after constructor -- (problems: this requires wrapping all subclasses)
Can I create a thunk to run after the constructor?
No, that is not possible.
How to run code after class fields are initialized, in a sane way?
Put the code in the constructor of the class that defines those fields.
Is there some way to implement some global logic for all subclasses in the parent class?
Yes: define a method. The subclass can call it from its constructor.
Just thought of a workaround (that is hierarchically composable). To answer my own question, in a somewhat unfulfilling way (people should feel free to post better solutions):
// The following illustrates a way to ensure all public class fields have been defined and initialized
// prior to running 'constructor' code. This is achieved by never calling new directly, but instead just
// running Someclass.make(...). All constructor code is instead written in an init(...) function.
class Superclass {
init(opts) { // 'constructor'
this.toRun(); // custom constructor logic example
}
static make() { // the magic that makes everything work
var R = new this();
R.init(...arguments);
return R;
}
}
class Subclass extends Superclass {
subclassValue = 0 // custom public class field example
init(toAdd, opts) { // 'constructor'
// custom constructor logic example
this.subclassValue += toAdd; // may use THIS before super.init
super.init(opts);
// may do stuff afterwards
}
toRun() { // custom public class method example
console.log('.subclassValue = ', this.subclassValue);
}
}
Demo:
> var obj = Subclass.make(1, {});
.subclassValue = 1
> console.log(obj);
Subclass {
subclassValue: 1
__proto__: Superclass
}
I tried doing
trace(classname.functionname.variablename);
//or
trace(classname.functionname().variablename);
Didn't work.. any idea, to get from the classname.as the variable, that's inside a function?
Btw i tried making the function static, still didn't work
Any idea?
There's no way, as those variables that are defined inside a function only live as long as the function is executed, and disappear once there's a return or end of function body. In order to get whatever value you want from a function, make a class variable outside the function, assign it the value you want within that function, and address it from elsewhere.
class test {
public static var foo:Number;
function bar():void {
// ... some code
foo=baz*2.54;
// ... more code
}
}
class elsewhere {
...
trace(test.foo);
...
}
the variables created inside a function are only available in the scope of that function.
if the variables are class member variables (declared public on a class);
public class x {
public var varName:String="";
}
you will be able to access them as
classInstanceRef.varName
needless to say you will need to instantiate from that class an instance.
Unless your variable is declared static on the class
public static varName:String="";
and in that case you can access it using
className.varName;
So I have a method that takes in a String and then is suppose to set the dynamic textbox on a button to said String.
public function setText(caption:String) {
this.btext.text = caption;
}
I really don't understand why this method is producing a 1119 error.
Access of a possibly undefined property btext through a reference with static type Button.as
The instance name of the Dynamic Textbox is btext and I have tried deleting the textbox and making a new one however this still produces a 1119 error. I also read on another stack question that trying this['btext'].text = caption; which gave me plenty of runtime errors.
Basically what am I doing wrong?
Thank you for any help.
EDIT
Here is the code I am using, and I create an instance of button add it to the stage and store it in an array with this code.
Code to create button
this.buttonArray.push(this.addChild(weaponButton));
Button.as
package {
import flash.display.MovieClip;
import flash.filters.*;
public class Button extends MovieClip {
public function Button() {
}
public function setPosition(xpos:int, ypos:int) {
this.x = xpos;
this.y = ypos;
}
public function setScale(xScale:Number, yScale:Number) {
this.scaleX = xScale;
this.scaleY = yScale;
}
public function addDropShadow():Array {
var dropShadow:DropShadowFilter = new DropShadowFilter(2,45,0, 1,4,4,1,1,true);
return [dropShadow];
}
public function removeDropShadow():Array {
return null;
}
public function setText(caption:String) {
this.btext.text = caption;
}
}
}
As you have stated btext is an instance name of an object. Here is where I assume btext is an object you created in your library.
In your class you are doing 2 things wrong. So lets examine your method.
public function setText(caption:String) {
this.btext.text = caption;
}
The first thing wrong is you are using "this". "this" is a reference to the current instance of the class you are in. And you are saying btext is a property on said instance. Which as I am assuming it is not because you defined btext as an object in your library. This will give you the property is undefined error you are gettting.
Now the second issue at hand is you are about to ask "OK how do I reference btext in my class then". What you need to know is that only objects added to the display list IE:stage can access objects via the stage.
You can do this 3 ways.
The first way is to pass a reference to the button into the class and store it as a property of the class.
The second way is to add your class to stage and in the class listen to the addedToStage event. At that time you can then access the object.
MovieClip(root)["btext"].text
The first 2 methods are not good practice since btext is not apart of the class and a general rule of thumb would be to encapsulate your class.
To make this work what you could do is have your class assign the value to a property in your class then fire an event and make the parent of this class listen to that event then just grab the value and assign.
Here is some suggested reading
I think the variable btext doesn't exist at all, or is it inherited from Movieclip?
say, Child class is inheriting Father class and Father class is inheriting spark TextArea class. now from an mxml file (in FLEX4), i am creating multiple objects of Child class. Father class have few static attributes whose values are set by private methods, calling from constructor. Now the question is: all these static attributes are set every time while Child class objects are being created one by one?
If answer is yes then Is it possible that Father class static attributes are set only once and not depends upon the number of Child class objects creation.
Please provide any suggestion or tips
Thanks in advance.
If you are setting static variables from an object's constructor or methods called from the constructor, then yes, they will be set every time. In order to prevent that, just check whether the variable is already set.
public class Foo {
public static var bar:Object;
public Foo(value:Object) {
if (!bar) {
bar = value;
}
}
}
First decide if those static members are really all that important to store as statics because statics are associated with a Class and not an instance it's usually a signal that you're probably doing something you shouldn't if instances are modifying or reading static members. You probably should use a factory method if you need to share that information with the instances. However, if you're sure you should do it then you can use a static initializer block to initialize the members when the class is loaded. Downside is that block throws an exception it can be hard to track down:
public class SomeObject {
private const _someStaticMember : String;
private const _someOtherStaticMember : SomeOtherObject;
static {
_someStaticMember = "foobar";
_someOtherStaticMember = new SomeOtherObject();
}
}
I am using Linq-To-SQL.
I have made one class by inheriting ObservableCollection
This class has one constructor with Datacontext as parameter.
I have calling this construtor from my program and assigning it to the control's ItemSource property.
But I can't get distinct value in it..
public class BindBookIssueDetails : ObservableCollection
{
public BindBookIssueDetails(DataClasses1DataContext dataDC)
{
foreach (Resource_Allocation_View res in dataDC.Resource_Allocation_Views)
{
this.Add(res);
}
}
}
private BindBookIssueDetails bResource;
bResource = new BindBookIssueDetails(db);
_cmbResource.ItemSource=bResource;
So what's the solution?
Plz Help...
I would first suggest taking your query logic out of the constructor of the collection. That's a very unusual place for something like that.
But otherwise, the LINQ function you're looking for is called Distinct.