anchor.diff:        }
   
       });
  -    
  +
       game.stage.onKeyUp.listen((value) {
         switch (value.keyCode) {
           case leftArrow:
  
positive.code:           break;
        }
      });
      
      
      List<Bullet> aliveBulletList = new List<Bullet>();    
      List<Ufo> aliveUfoList = new List<Ufo>();
      aliveUfoList.addAll(ufos.where((item)=>item.alive));
      
      game.stage.onEnterFrame.listen((_){
        if( aliveUfoList.length <= 0 ){
          killteState();
        }
        
        aliveBulletList.addAll(bullets.where((item)=>item.alive));
        
        aliveBulletList.forEach((bullet){
          aliveUfoList.forEach((ufo){
            if(ufo.hitTestObject(bullet)){
              ufo.alive = false;
              bullet.alive = false;           
            }
          });
        });
        
        aliveUfoList.removeWhere((item)=>!item.alive);
        
      });
  
    }
  
negative.code: part of spaceinvader;
  
  class Play extends State {
    Play(String name, [String nextState]) : super(name, nextState);
  
    run() {
      Background background = new Background(800, 600, mainColor);
      game.stage.addChild(background);
  
      Ship player = new Ship(this, "ship")
          ..center()
          ..x = 400
          ..y = 500
          ..vx = 200;
  
  
      game.stage.addChild(player);
      game.stage.juggler.add(player);
  
      List<Bullet> bullets = new List<Bullet>();
      for (int i = 0; i < 5; i++) {
        bullets.add(new Bullet(this, "bullet")..center()..vy=300);
      }
  
      /*Group<Bullet> bulletGroup = new Group<Bullet>();
      bulletGroup.addChildByFunction(()=> new Bullet(game.resourceManager.getBitmapData("bullet")));
      print(bulletGroup.getChildAt(0));*/
  
      Ufo ufo;
      List<Ufo> ufos = new List<Ufo>();
      for (int i = 1; i < 8; i++) {
        ufo = new Ufo(this, "ufo")
            ..center()
            ..x = (i * 100)
            ..y = 50
            ..vy = 50
            ..alive = true;
        ufos.add(ufo);
        game.stage.addChild(ufo);
        game.stage.juggler.add(ufo);
  