how do I access the main class's stage? + Can I pass functions as arguments like this?

There are two files in my actionscript project named "TestAPP", TestAPP.as and Draggable.as

TestAPP.as:

    package {
 import flash.display.Sprite;
 im开发者_如何转开发port flash.display.Stage;

 public class TestAPP extends Sprite
 {
  var _mainStage:Stage;
  public function TestAPP()//This is where we test the UI components.
  {

   var sp:Sprite = new Sprite();
   _mainStage = stage;
   _mainStage.addChild(sp);
   sp.graphics.beginFill(0x00FF00);
   sp.graphics.drawCircle(0,0,10);
   sp.graphics.endFill();
   sp.x = 50;
   sp.y = 50;
   var draggable1:Draggable = new draggable(sp,_mainStage,limitingfunc);
  }
  public function limitingfunc(x:Number,y:Number):int{
   return 0;
  } 

 }
}

And for the draggable.as:

package
{
 import flash.display.Sprite;
 import flash.display.Stage;
 import flash.events.MouseEvent;

 public class Draggable
 {
  private var _limitingFunc:Function;
  private var _which:Sprite;
  private var _MouseSavedX:Number;
  private var _MouseSavedY:Number;

  private var _stage:Stage;
  public function Draggable(which:Sprite,stage:Stage,limitingfunc:Function)
  {
   _limitingFunc = limitingfunc;
   _which = which;
   _stage = stage;
   _which.addEventListener(MouseEvent.MOUSE_DOWN,begin_drag);

  }
  //limiting func: returns 0 when the object is free to move that place.
  //returns -1 when the user wants to block X coordinate changes (but maintain Y free)
  //returns -2 when the user wants to block Y ...
  //returns -3 or less when the user wants to block both X and Y from changing.
  //returns
  private function Return_0(x:Number = 0,y:Number = 0):int{
   return 0;
  }
  private function begin_drag(ev:MouseEvent):void{
   var xTo:Number = _stage.mouseX - _MouseSavedX + _which.x;
   var yTo:Number = _stage.mouseY - _MouseSavedY + _which.y;
   var limitingFuncReturnValue:int = _limitingFunc(xTo,yTo);
   if(limitingFuncReturnValue == 0){//free to move.
    _which.x = xTo;
    _which.y = yTo;
   }
   else if(limitingFuncReturnValue == -1){//free to move Y
    _which.y = yTo;
   }
   else if(limitingFuncReturnValue == -2){
    _which.y = yTo;
   }
   //else:do nothing.
  }
 }
}

In "my actionscript theory", I'm supposed to see a circle that follows the mouse when I click it. (The draggable is not fully implemented) But the circle doesn't even budge :(

...I've been trying to figure out how to access the main class's stage property. I've googled for it, but still no progress.

Please help this helpless newb!!! I'll really appreciate your help:) Thank you!

You're implementing your 2nd class as "draggable", when you named it (and it has to be named) "Draggable" with an upper case. Change it and see if that works. You seem to be passing in the parent classes stage correctly though.

If TestAPP is your document class. You can access to the stage thru the stage property (like your are doing in your example). If TestAPP is not the document class, you should listen first to the ADDED_TO_STAGE event and then access to the stage property. There is no need to add _mainStage property because you already have the stage property. In order to move objects around, you need to use the ENTER_FRAME event.

You can access the main class' stage property the same way you do it for any DisplayObject on the stage: Use this.stage.

So just this should be enough:

var sp:Sprite = new Sprite();
stage.addChild(sp);

You could then pass the sprite and the main class' stage as a parameter, the way you did - but I would recommend creating a subclass Draggable extends Sprite and instantiate the whole thing using new Draggable() instead.
The new object will automatically have its own reference to stage as soon as it is added to the display list, and limitingFunc could be a member of Draggable, as well.

Also, you can use the startDrag() and stopDrag() methods, no need to implement your own: You can specify a Rectangle as a parameter to startDrag() to limit the permitted movement.

if you need it so much you may:

private static var _instance: TestAPP;
//...
public function TestAPP(){
    _instance = this;
    //...
}

public static function get instance():TestAPP{
    return _instance;
}

public static function set instance(newVal: TestAPP):void{
    _instance = newVal;
}

and you'll be able to reference its stage from any class where your TestAPP will be imported just with TestAPP.instance.stage.
but _instance is a property of the class TestAPP itself, not its instances