unity3d - Unity 2D - HP bar -

the value of hp bar drops when runner collides obstacle. of course, value of hp drop nomally, image of hp bar not change. why error?

public class csrunner : monobehaviour {     public vector2 jumpvelocity;     public float _hp = 100f;     public float _curhp;     bool isjump;     public image _hpvalue;      bool collision_box;      // use initialization     void start()     {         _hpvalue = gameobject.find("hpbar").getcomponent<image>();         _curhp = _hp;     }      // update called once per frame     void update()     {         _hpvalue.fillamount = _curhp / _hp;          if (input.getkeydown(keycode.space) && isjump)         {             isjump = false;             transform.getcomponent<rigidbody2d>().addforce(jumpvelocity/2, forcemode2d.impulse);         }          if ((input.getkeydown(keycode.space) || input.getmousebuttondown(0)) && collision_box)         {             isjump = true;             transform.getcomponent<rigidbody2d>().addforce(jumpvelocity, forcemode2d.impulse);         }          else         {             getcomponent<animator>().settrigger("run");         }     }      void ontriggerenter2d(collider2d coll)     {         if (coll.transform.tag == "enemy")         {             _curhp--;             _hpvalue.fillamount = _curhp / _hp;         }     } } 

here screenshot of scene :

thank !