calling movieclip of a class from another class, error#1009 - actionscript-3

Question

i got error: method of null object reference. I'm so confused and don't know what is the real cause.
So i got a player movieClip on the stage which has an instance of "player_mc", which will be pass thru my Document class and into the Player class.
Player.as
import flash.display.*;
import flash.events.*;
public class Player extends MovieClip
{
public var myPlayer:MovieClip;
public function Player(player:MovieClip)
{
myPlayer = player;
addEventListener(Event.ENTER_FRAME,on_enter);
}
Document.as
import flash.display.*;
import Components.Player.Player;
public class Game_Main extends MovieClip
{
public var player:Player;
public function Game_Main()
{
player = new Player(player_mc);
}
}
now here i think is where the problem comes from. I have a green_enemy movieclip on the stage which has base class Enemy.
Enemy.as
import flash.display.MovieClip;
import Components.Player.Player;
import flash.events.Event;
public class Enemy extends MovieClip
{
var theplayer:Player;
public function Enemy()
{
this.addEventListener(Event.ENTER_FRAME,on_enter);
}
public function on_enter(e:Event):void
{
if (this.hitTestObject(theplayer.myPlayer)) //calls player_mc from Player class
{
trace("hi");
}
}
}
what I like to do on Enemy function is when Enemy collides with "player_mc" (which is on the stage) it will do something. Maybe my code is wrong.
Any help/tips will be appreciated. Thanks!

Answer 1

In your Enemy.as I see
var theplayer:Player;
not initialized. It is private, so you can not define it from outside. That means that exception comes from here
this.hitTestObject(theplayer.myPlayer)
You are trying to call myPlayer from null.
Try to define this variable while constructing Enemy class.
To prevent null exception you can check if theplayer is null
public function on_enter(e:Event):void
{
if (theplayer && this.hitTestObject(theplayer.myPlayer))
{
trace("hi");
}
}

Answer 2

To expand on what ZuyEL said, your variable isn't globally defined in your enemy class since you're just adding a var inside your enemy function. Instead, do the following
public var thePlayer:Player;
write the above after your Enemy class, before the Enemy function. Now it is available to the whole class and will no longer be null when you call it later.