How to create a damage bar for a shooting game on iPhone?

I have a question in game development. I am building a game for iPhone. At the game play, there is a damage bar, that displays what the player has damage the enemies. The technique I use is using 2 pictures. One is a damage bar which is fill with full damage, and one is jus a black bar but same size with the damage bar. It is like masking. I will scale the black bar shorter whenever it receives the value of the damage. But the problem here is the method i use to calculate the damage is different class from the method i use to draw the black bar. How do I draw it frequently everytime it gets a damage value? please help me , thank you开发者_JS百科 so much.

-(void)damageTaken
{
    totalDamage = 0;
    for (uint i = 0 ; i< [bodyParts count]; i++) {
        RagdollBodypart *part = (RagdollBodypart *)[bodyParts objectAtIndex:i];
        totalDamage += part.damage;
    }
    [[NSNotificationCenter defaultCenter] postNotificationName:DAMAGE_TAKEN object:nil];
}

above is the method I used to calculate the damage. It will get called everytime the player hits something. It is created in a class called BodyDamage

This is the code i use to draw the mask for the damage bar. it just runs once, how can I run this with the number of time same as the damageTaken?

 float damage = [[GameController instance].engine.enemies totalDamage];
                        float scale = (float)(1400 -damage)/(float)1400;
                        [damageSprMask setScaleY:scale];
                        //[damageSprMask setPosition:ccp(20,150)];
                        [damageSprMask setPosition:ccp(20,150 +((1- damageSprMask.scaleY)*damageSpr.contentSize.height)/2)];

---

To cause a view to redraw itself you can use [view setNeedsDisplay] this will trigger the drawRect method for the view.

So you can either call directly in damageTaken or in the method that listens for the notification you're sending.

---

Thanks for ur reply. I solved the problem now. What I did was just create another tick function. I will call that function 60 times in a second same as my framerate then draw the mask in there. My damage bar looks fine now. But thank you too, I think your way works as swell.