Adding custom properties to SKNode and using them with 'enumerateChildNodesWithName:usingBlock:' - objective-c

Question

What I wish to do is: to extend SKNode with a custom property, a plain int, and later use it with enumerateChildNodesWithName:usingBlock:.
Since I am a total beginner I failed to understand tutorials of how to do this with the 'userData' property of SKNode. I also attempted to create a subclass of NSObject/SKNode and adding the property there. But then I failed to make it work with enumerateChildNodesWithName:usingBlock:.
Extending SKNode seemed more straight forward to me.
the compiler does not complain about the following code:
SKNode_weight.h
#interface SKNode ()
#property int weight;
#end
MyScene.h
#import "SKNode_weight.h"
MyScene.m
#import "MyScene.h"
#import "SKNode_weight.h"
#implementation MyScene
-(void) spawnBall {
SKNode *ballNode = [SKNode node];
ballNode.weight = 10; // fixed value for simplicity
ballNode.name = #"ball";
[self addChild:ballNode];
}
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
[self spawnBall];
}
return self;
}
-(void) sumWeight{
[self enumerateChildNodesWithName:#"ball" usingBlock:^(SKNode *node, BOOL *stop) {
NSLog(#"%i", node.weight);
}];
}
#end
the build is successful, but I get the following error:
-[SKNode setWeight:]: unrecognised selector sent to instance 0x96328f0
I hope somebody can give a an example of a quick and painless solution.
Thank you, Flo

Answer 1

It is not possible to add members and properties to an existing class via a category — only methods.
http://developer.apple.com/library/ios/#documentation/General/Conceptual/DevPedia-CocoaCore/Category.html
Best way would be to subclass SKNode and add weight property to the subclass.
SKNodeWeighted.h
#interface SKNodeWeighted : SKNode
#property int weight;
#end
Then use it like you would use the category with slight differences.
#import "MyScene.h"
#import "SKNodeWeighted.h"
#implementation MyScene
-(void) spawnBall {
SKNodeWeighted *ballNode = [SKNodeWeighted node];
ballNode.weight = 10; // fixed value for simplicity
ballNode.name = #"ball";
[self addChild:ballNode];
}
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
[self spawnBall];
}
return self;
}
-(void) sumWeight{
[self enumerateChildNodesWithName:#"ball" usingBlock:^(SKNode *node, BOOL *stop) {
if ([node isKindOfClass:[SKNodeWeighted class]]) {
NSLog(#"%i", ((SKNodeWeighted*)node).weight);
}
}];
}
#end