SKSpriteNode loses its physicsBody properties - ios

Question

I'm using SpriteKit to create a game in which objects at the bottom of the map move.
The objects are crocodiles and coins.
The scene uses an NSTimer to that calls this selector:
timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:#selector(generateBottomSprite) userInfo:nil repeats:YES];
-(void) generateBottomSprite{
int random = (arc4random() % difficulty+3) + difficulty-3;
if (counter >random){
SKSpriteNode *bottomSprite;
if (random>difficulty){
bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:#"crocodile"];
bottomSprite.size = CGSizeMake(70, 120);
bottomSprite.physicsBody.categoryBitMask = crocMask;
}else{
bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:#"coin"];
bottomSprite.size = CGSizeMake(50, 50);
bottomSprite.physicsBody.categoryBitMask = coinMask;
}
//create a crocodile
bottomSprite.position = CGPointMake(self.frame.size.width,bottomSprite.frame.size.height/2);
bottomSprite.name = #"bottomSprite";
[self addChild: bottomSprite];
counter = 0;
[self enumerateChildNodesWithName:#"bottomSprite" usingBlock: ^(SKNode *node, BOOL *stop) {
node.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:node.frame.size];
node.physicsBody.affectedByGravity = NO;
node.physicsBody.mass = 8000.0;
node.physicsBody.friction = 2.50;
node.physicsBody.usesPreciseCollisionDetection = YES;
}];
}
}
The problem: all the physicsWorld's properties are re-initialized on each call to the selector and i must iterate over the children of the scene in order to re-assign them.
Why are the properties get re-initialized?

Answer 1

you are setting the categorybitmask before creating the skphysicsbody itself
bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:#"crocodile"];
bottomSprite.size = CGSizeMake(70, 120);
//add the following
bottomSprite.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:bottomSprite.frame.size];
///////////////
bottomSprite.physicsBody.categoryBitMask = crocMask;
move all the physics settings outside the enumeration like so
if (counter >random){
SKSpriteNode *bottomSprite;
int currentBitMask;
if (random>difficulty){
bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:#"crocodile"];
bottomSprite.size = CGSizeMake(70, 120);
currentBitMask = crocMask;
}else{
bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:#"coin"];
bottomSprite.size = CGSizeMake(50, 50);
currentBitMask = coinMask;
}
**bottomSprite.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:bottomSprite.frame.size];**
bottomSprite.physicsBody.categoryBitMask = currentBitMask ;
bottomSprite.physicsBody.affectedByGravity = NO;
bottomSprite.physicsBody.mass = 8000.0;//way too high
bottomSprite.physicsBody.friction = 2.50;//probably high
bottomSprite.physicsBody.usesPreciseCollisionDetection = YES;//overkill, set only if critical
//create a crocodile
bottomSprite.position = CGPointMake(self.frame.size.width,bottomSprite.frame.size.height/2);
bottomSprite.name = #"bottomSprite";
[self addChild: bottomSprite];
you also might wanna make use of the update method in the skscene and nstimeintervals to measure time till you pass half a second then call the generateBottomSprite method, it should be more efficient than using an additional NSTimer.
Feel free to ask if anything is unclear, hope this helps.