How to change the value of a certain variable in the document class through another class?

Question

here is my problem. In my document class TowerDefenseGame.as, I defined a variable Turrent1Flag:

package 
{
import flash.display.MovieClip;
import flash.events.*;
import flash.display.Sprite;
import flash.display.Shape;
import flash.text.TextField;
import flash.text.TextFormat;
import flash.text.TextFieldType;

public class TowerDefenseGame extends MovieClip
{
       public var Turrent1Flag==0;
}

public function TowerDefenseGame()
{
  ......
}

Now, in another class Turrent1Button.as, I need to create a mouse click event, by which the Turrent1Flag is set to 1:

package 
{
import flash.display.MovieClip;
import flash.events.*;
import flash.display.Sprite;
import TowerDefenseGame;

public class TurretButton1 extends MovieClip
{
    public var ButtonBase:Sprite=new Sprite();
    public var TurretBase:Sprite=new Sprite();
    public var Gun:Sprite=new Sprite();

    public function TurretButton1()
    {
               ......
       this.addEventListener(MouseEvent.CLICK, MouseClick);
    }

    public function MouseClick(event:MouseEvent):void
    {
        MovieClip(root).Turret1Flag = 1;
    }

Well, this does not work. I am using Adobe flash cs6 and it says the value cannot be accessed. Someone know how to do this?

Answer 1

So, to start out, AS3 makes it difficult to so what you've been used to doing in AS2 on purpose, to allow for better Object Oriented practices. When you maintain high and tight walls between Classes, it becomes easier to change Class A without having any effect whatsoever on Class B. Class B only knows about the doors and windows that are the "official" ways into the house of Class A, so it doesn't matter if you move the couch. You also make it extremely easy to replace Class A with Class C that has similar doors and windows.

When you reach through the walls by introducing global state, you can't replace Class B with Class C without changing Class A, because Class A has a direct reference to Class B and knows exactly where the couch is.

One way to handle this is through Inversion of Control (IoC). So, for our house, the couch might be supplied from outside and whatever component supplied it might keep a reference to it, so it would be able to access the couch no matter where in the house it went. So, you might choose to create your TurretButton and pass that into whoever owns that, while your TowerDefenseGame keeps a reference to it and listens directly to it, changing its own flag in response to the click.

Looking at your code, you probably don't need to go that far, because I don't see any sign that your TurretButton is actually nested. In that case, you can listen directly to it, whether you're creating it on the stage or creating it through code (which I'm not a fan of). If you're using the stage in the IDE and it exists on the stage, then just create a public variable of type TurretButton (or you could probably use SimpleButton since you no longer have need for a special Class here based on the code you've shown). That instance will be available in the constructor of your TowerDefenseGame. Just add your event listener to it, and then the listener and the variable you want to change are in the same scope. Ergo, the problem you were trying to solve never existed--you were simply looking at the problem from a perspective that overcomplicated things.

If, in fact, your code is nested in a way that's not shown, you can use ActionScript 3's event system, which is fabulous, to handle the issue without introducing direct coupling and without having to create the button through code and push it down to where it's used. One way is to just listen for any mouse click (since that is a bubbling event) and look to see what was clicked. Another solution is to generate a custom event from the button that you can then listen to from the top level to change the flag. That would look something like:

package view.button {
   public class TurretButton extends MovieClip {
      public function TurretButton() {
         super();
         mouseChildren = false;
         addEventListener(MouseEvent.CLICK, broadcastTurretEvent);
      }
      protected function broadcastTurretEvent(e:Event):void {
         dispatchEvent(new Event('turretClicked', true));//the true parameter makes it bubble
      }
   }
}

Then your tower Class would look like

package {
   public class TowerDefenseGame extends MovieClip {
      //the fact that you're calling it Turret1Flag suggests you're going to have more than 1
      protected var turretFlags:Array /*of Boolean*/ = [false, false];
      //your turret button instances  
      //doesn't show nesting, this is just to indicate that
      //these are named instances so you know how what they're called
      //they could be nested at any level    
      public var turret1:TurretButton;
      public var turret2:TurretButton;
      //...etc.
      public function TowerDefenseGame() {
         super();
         addEventListener('turretClicked', onTurretClicked);
      }
      protected function onTurretClicked(e:Event):void {
         //you can also just extract the number and do the math
         //to get the correct array index
         switch(e.target.name) {
            case 'turret1':
               turretFlags[0] = !turretFlags[0];
               break;
            case 'turret2':
               turretFlags[1] = !turretFlags[1];
               break;
         }
      }
   }
}

Note how well this scales. You don't have to have a different Class for each button to change each separate flag. It's also easy to add more buttons without a whole lot of code changes. You could take this solution further and create a custom event that has a property that says which button was clicked, and you could supply the value to use to that for the button through dependency injection, etc.

I also made the assumption in my code that flags should be boolean and that they're turning on with the first click and off with the second click, etc. You could take the same idea and change it to, for example, increment with every click. I suspect you don't actually want to do what your code was showing and just turn it on with the first click and just leave it on forever.

Another note is that if you think you might want to code in AS3 over the longer term, you should probably learn the coding conventions that are used in AS3. One of these is that Class names start with a capital letter, but properties and methods do not.

Answer 2

It's probably not a great habit to get into for everything, but a static variable looks like it would work here.

public class TowerDefenseGame extends MovieClip
{
    public static var Turrent1Flag = 0;
}

In Turrent1Button.as:

public function MouseClick(event:MouseEvent):void
{
    TowerDefenseGame.Turret1Flag = 1;
}

Answer 3

try this:

private static var _instance:TowerDefenseGame;
public static function get instance():TowerDefenseGame { return _instance; }

public function TowerDefenseGame() 
{
    _instance = this;
}

---

public function MouseClick(event:MouseEvent):void
{
       TowerDefenseGame.instance.Turret1Flag = 1;
}