iPhone, Cocos2D - moving sprite left/right while touching screen

Question

I'm new to Objective C and app development so please go easy on me! I'm trying to make a basic game and need to move a sprite left or right continuously while the user's finger is on the screen - left side to go left, right to go right... I'm trying to use update to repeat movements of a few pixels every 1/60th second. So far, this is what I have (and sorry about the formatting):

    #import "GameplayLayer.h"

    @implementation GameplayLayer

    -(id)init {
         self = [super init];
         if (self != nil) {
         CGSize screenSize = [CCDirector sharedDirector].winSize;  
          // enable touches
         self.isTouchEnabled = YES;  

     blobSprite = [CCSprite spriteWithFile:@"blob.png"];
    [blobSprite setPosition: CGPointMake(screenSize.width/2, screenSize.height*0.17f)];

    ball = [CCSprite spriteWithFile:@"ball.png"];
    [ball setPosition:CGPointMake(10, screenSize.height*0.75f)];

    [self addChild:blobSprite];  
    [self addChild:ball];

    [self schedule:@selector(update) interval:1.0f/60.0f];

   }
   return self;
 }



    -(void) update:(ccTime)dt{
      if (_tapDownLeft == YES){
         blobSprite.position.x==blobSprite.position.x-5;
      }
     if (_tapDownRight == YES){
         blobSprite.position.x==blobSprite.position.x+5;
     }
    }


-(void) ccTouchesBegan:(UITouch*)touch withEvent: (UIEvent *)event{

 CGPoint touchLocation = [touch locationInView:[touch view]];
 touchLocation = [[CCDirector sharedDirector] convertToGL:touchLocation];

if (touchLocation.x > 400) {
   if ((blobSprite.position.x+10)<460){
           _tapDownRight = YES;
      }
}

if (touchLocation.x < 200) {
    if ((blobSprite.position.x-10>20)){
           _tapDownLeft = YES;
      } 
}

else {
    _tapDownLeft = NO;
    _tapDownRight = NO; 
      }   
}
 -(void)ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event{
      _tapDownLeft = NO;
      _tapDownRight = NO;
      }



-(void) registerWithTouchDispatcher{
  [[CCTouchDispatcher sharedDispatcher]addTargetedDelegate:self priority:0                            swallowsTouches:YES];
}


@end

Am I on the right lines with this? At the moment it's giving me 'expression result unused' in update. Could anyone tell me what I'm missing? Any help would be greatly appreciated.

Thanks, Patrick

Answer 1

i see a few things here:

• not certain your selector will call update : @selector(update:)
• I would not rely on dt being either exactly 1/60th of a second, nor being constant. I would favor defining a speed constant (in points per second) and compute the deltaX in points based on the desired speed and dt, at each update cycle.
• I dont see a 'registerWithTouchDispatcher' call (i try to place them in onEnter and onExit) methods.
• Somewhere in there, make certain you remove your children (either in dealloc, or better in a local cleanup method (dont forget to invoke [super cleanup]).