ComputerNode doesn't show up Objective-C

Question

I try to make pong like game were on one side is player and on other side computer, because I want to in future add many game scenes with different gamefields I create ball node, paddle node etc.files separately, to make it easier to insert in gamefields and I don't have them create on every scenes from scratch.
The Problem Now when I try everything put together player paddle works, ball node works, but computer paddle shows up for second and then disappears. Here are what I got in: GameScene.m

@implementation GameScene

-(void)didMoveToView:(SKView *)view {

self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
self.physicsBody.categoryBitMask = gamefieldCategory;
self.physicsBody.contactTestBitMask = emptyCategory;
self.physicsWorld.contactDelegate = self;

BallNode *ball = [[BallNode alloc] init];
[self addChild:ball];
ball = (BallNode *) [self childNodeWithName:@"ball"];
[ball resetPosition];

PlayerNode *leftPlayer = [[PlayerNode alloc] initOnLeftSide];
[self addChild:leftPlayer];
leftPlayer = (PlayerNode *) [self childNodeWithName:@"leftPlayer"];
[leftPlayer positionOnLeftSide];

ComputerNode *rightPlayer = [[ComputerNode alloc] initOnRightSide];
[self addChild:rightPlayer];
rightPlayer = (ComputerNode *) [self childNodeWithName:@"rightPlayer"];
[rightPlayer positionOnRightSide];    
}
-(void)computer{
BallNode *ball = (BallNode *) [self childNodeWithName:@"ball"];
ComputerNode *rightPlayer = (ComputerNode *) [self childNodeWithName:@"rightPlayer"];    
if (ball.position.x > CGRectGetMidX(self.frame)) {
    if (rightPlayer.position.y > ball.position.y) {
        rightPlayer.position = CGPointMake(self.frame.origin.x - 50 + self.frame.size.width, rightPlayer.position.y -1.5f);
   //there is a very long text, thats why i cut it off
    }
  }
- (void)update:(CFTimeInterval)currentTime{
      [self computer]; // calling computer paddle movement.
 }

ComputerPaddleNode.m

@implementation ComputerPaddleNode
- (id)init
 {
return [self initWithName:@"paddle"];
 }

 - (id)initWithName:(NSString *)name
 {
  self = [super init];
  if (self) {

    self = [ComputerPaddleNode spriteNodeWithImageNamed: @"board.png"];
    self.userInteractionEnabled = YES;
    self.name = name;
    self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size];
    self.physicsBody.dynamic = NO;
    self.physicsBody.usesPreciseCollisionDetection = YES;
    self.physicsBody.categoryBitMask = paddleCategory;
    self.physicsBody.collisionBitMask = emptyCategory;

}

return self;
}

- (BOOL)withinParentFrame:(CGPoint)point
 {
CGFloat offset = self.size.height / 2;
if (point.y >= offset && point.y <= self.scene.frame.size.height - offset)
    return YES;
else
    return NO;
}
 - (CGPoint)normalisePoint:(CGPoint)point
{
CGFloat x = point.x / (self.size.width / 2);
if (x > 1.0)
    x = 1.0;
else if (x < -1.0)
    x = -1.0;

CGFloat y = point.y / (self.size.height / 2);
if (y > 1.0)
    y = 1.0;
else if (y < -1.0)
    y = -1.0;

return CGPointMake(x,y);
  }
@end

ComputerNode.m

@implementation ComputerNode
-(id)init
 {
        return [self initOnRightSide];
  }
 - (id)initOnRightSide
  {
  self = [super init];
     if (self) {
      self.name = @"rightPlayer";
    ComputerPaddleNode *rightPaddle = [[ComputerPaddleNode alloc] initWithName:@"rightPaddle"];
    [self addChild:rightPaddle];
    ScoreNode *score = [[ScoreNode alloc] initWithName:@"rightScore"];
    [self addChild:score];
    }
  return self;
   }
  - (void)positionOnRightSide
   {
SKNode *paddle = [self childNodeWithName:@"rightPaddle"];
paddle.position = CGPointMake(CGRectGetMaxX(self.parent.frame) -50, CGRectGetMidY(self.parent.frame));  
}
@end

Why Computer node disappears and what do I need to change that?

Answer 1

In this code snippet

- (void)positionOnRightSide
   {
     SKNode *paddle = [self childNodeWithName:@"rightPaddle"];
     paddle.position = CGPointMake(CGRectGetMaxX(self.parent.frame) -50, CGRectGetMidY(self.parent.frame));  
   }

you are positioning self's child paddle in the coordinate system of the self's parent's parent (self's "grandparent"). Remember a node's frame already refers to its parent's coordinate system.

This might be the reason your right player's paddle is disappearing on you.