SpriteKit collision Detection does not work - ios7

Question

I thought I understand the concepts of bitmasks, CategoryBitMasks and CollisionBitMasks, but it turns out I am not ;-(
but I dont understand why.
I set the bit Masks for collision detection, I add the category Bit mask to the frame, and I add the categoryBitMask to my object (in this case a taxi). But the taxi just drops down the screen :-/
Any ideas why this is like that?
#import "MyScene.h"
#import "SKSpriteNode+DebugDraw.h"
// Define Bit Masks for Collision Detection
typedef NS_OPTIONS(uint32_t, CNPhysicsCategory) {
CNPhysicsCategoryEdge = 1 <<0,
CNPhysicsCategoryTaxi = 1 <<1,
};
#interface MyScene() <SKPhysicsContactDelegate>
#end
#implementation MyScene{
SKNode *_gameNode;
SKSpriteNode *_taxiNode;
}
-(instancetype)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
[self initializeScene];
}
return self;
}
-(void)initializeScene{
self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
self.physicsWorld.contactDelegate = self;
self.physicsBody.categoryBitMask = CNPhysicsCategoryEdge;
SKSpriteNode* bg = [SKSpriteNode spriteNodeWithImageNamed:#"background.png"];
bg.position = CGPointMake(self.size.width/2, self.size.height/2);
[self addChild: bg];
[self addTaxi];
_gameNode = [SKNode node];
[self addChild:_gameNode];
}
-(void)addTaxi{
_taxiNode = [SKSpriteNode spriteNodeWithImageNamed:#"taxi.png"];
_taxiNode.position = CGPointMake(self.size.width/2, self.size.height/2);
[self addChild:_taxiNode];
CGSize contactSize = CGSizeMake(_taxiNode.size.width, _taxiNode.size.height);
_taxiNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize: contactSize];
[_taxiNode attachDebugRectWithSize:contactSize];
_taxiNode.physicsBody.categoryBitMask = CNPhysicsCategoryTaxi;
}

Answer 1

I finally managed it - the problem was not the collision detection, but it was the layout of the phone, since I did not replace the viewDidLoad method in the ViewController with viewWillLayoutSubviews method.
Now everything works fine.
The significant post was the following: bodyWithEdgeLoopFromRect not working in landscape
Thanks for your support!