Unity 3D实现血量增加减少

HUDText ht;
UISprite sprite;
bool isjia = false;
bool isjian = false;

// Use this for initialization
void Start () {
ht = GetComponent<HUDText>();
sprite = GetComponent<UISprite>();
}
int blood = 100;
void OnGUI()
{
if (GUILayout.Button("加血"))
{

isjia = true;
}
if (GUILayout.Button("减血"))
{
isjian = true;
}
}

// Update is called once per frame
void Update () {
if (isjia)
{
ht.Add(-10, Color.red, 2f);
sprite.spriteName = "image 10002";
isjia = false;
}
if (isjian)
{
ht.Add(+10, Color.green, 2f);
isjian = false;
}
}