Sprite doesn't move upon collision - ios

Question

When I detect collision with a sprite, I want it (fuelSprite) to move to a new randomly generated position.
I generate the sprite like this
//setup fuel
SKSpriteNode *fuel = [SKSpriteNode spriteNodeWithImageNamed:#"fuel.png"];
fuel.position = CGPointMake(arc4random_uniform(self.frame.size.width), arc4random_uniform(self.frame.size.height));
[fuel setScale:0.6];
fuel.zPosition = 1;
fuel.shadowCastBitMask = 1;
fuel.name = #"fuelNode";
fuel.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:fuel.frame.size];
fuel.physicsBody.dynamic = FALSE;
fuel.physicsBody.affectedByGravity = false;
fuel.physicsBody.usesPreciseCollisionDetection = YES;
fuel.physicsBody.categoryBitMask = fuelCategory;
fuel.physicsBody.collisionBitMask = fuelCategory | fireCategory;
fuel.physicsBody.contactTestBitMask = fireCategory;
[self addChild:fuel];
[_items addObject:#"fuelNode"];
Then when collision is detected I want to grab the sprite (only thing in the array) and move it
-(void)didBeginContact:(SKPhysicsContact *)contact
{
NSLog(#"contact detected");
SKPhysicsBody *firstBody;
SKPhysicsBody *secondBody;
if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask)
{
firstBody = contact.bodyA;
secondBody = contact.bodyB;
}
else
{
firstBody = contact.bodyB;
secondBody = contact.bodyA;
}
NSLog(#"Hit");
score ++;
SKSpriteNode *object = [_items firstObject];
object.position = CGPointMake(arc4random_uniform(self.frame.size.width), arc4random_uniform(self.frame.size.height));
}
This is in my header file for the fuelSprite and items array
#property (nonatomic, strong) SKSpriteNode *fuelSprite;
#property (nonatomic) NSMutableArray *items;
For some reason I can't get the sprite to move to a new random location :(
The hit detection is working flawless and the NSlog shows that

Answer 1

You are adding a string to the array not a sprite. Try replacing
[_items addObject:#"fuelNode"];
with
[_items addObject:fuel];
Also, since this statement
SKSpriteNode *object = [_items firstObject];
returns an NSString not an SKSpriteNode, using object as a sprite should have caused an exception. I suspect that object is nil because your array wasn't properly allocated.
You can access the sprite in the scene with
SKSpriteNode *object = [self childNodeWithName:#"fuelNode"];
instead of adding it to an array.

Answer 2

Haven't done SpriteKit for a while but instead of setting the position.
Try replacing:
object.position = CGPointMake(arc4random_uniform(self.frame.size.width), arc4random_uniform(self.frame.size.height));
with:
CGPoint randomPoint = CGPointMake(arc4random_uniform(self.frame.size.width), arc4random_uniform(self.frame.size.height));
CGFloat duration = 2;
SKAction *move = [SKAction moveTo:randomPoint duration:duration];
[ojbect runAction:run];
Hopefully this works for you. :)

Answer 3

The reason is apple prevents you from messing with a node attached to a physicsBody.
You have two options:
A
SKPhysicsBody* tmp = object.physicsBody;
object.physicsBody = nil;
object.position = CGPointMake(arc4random_uniform(self.frame.size.width), arc4random_uniform(self.frame.size.height));
object.physicsBody = tmp;
Why is this bad? Because this way you detach your physics object from your actual node and they may be in two different places at the same time - you don't want that but in some cases it doesnt matter - then you can use this.
B
Create a new physics body at the position you need it to be and attach it back to your node