Accessing a property of a node - objective-c

Question

I currently have a SpriteKit game with the objective of shooting down enemies. I've implemented collision detection for it, and it works just fine. But I need to implement health for enemies. Enemies are constantly generated and keep moving, so you never know what node that should bebeSo I tried to declare my custom class node in didBeginContact method, then assigning it to bodyA, then changing it's health value, but this seems useless since I just create a new node (same shows the NSLog). I tried typecasting the declaration, but still with no luck. Did some research on this topic, but didn't find anything that suits me. Currently I can't provide source code for what I did, but I hope what I have requested is possible to explain. Please push me in the right direction.

Answer 1

Every SKSpriteNode has a userData NSMutableDictionary which can be used to store data (objects).
You first have initialize the dictionary like this:
myNode.userData = [NSMutableDictionary dictionary];
Then you can assign data to it like this:
float myHealth = 100.0;
NSString *myX = [NSString stringWithFormat:#"%f",myHealth];
[myNode.userData setValue:myX forKey:#"health"];
To read data you do this:
float myHealth = [[myNode.userData objectForKey:#"health"] floatValue];
I used float in my example but you can use whatever you want. Just remember that you cannot store primitives like float, int, long, etc... directly. Those need to be converted to NSNumber, NSString and so on.
That being said, Stephen J is right with his suggestion. You should subclass SKSpriteNode for your enemies and have health as a class property. Subclassing is much easier to work with in the long run and gives you greater flexibility compared to using the userData.

Answer 2

To illustrate some Object oriented concepts Stephen J and sangony are referring to, I have added some code for you.
Subclassing SKNode will define a new object class which inherits all functionality from SKNode. The main advantage here is that you can implement custom properties (such as health) and custom logic (such as lowering that health).
#interface EnemyNode : SKSpriteNode
- (void)getHit;
- (BOOL)isDead;
#property (nonatomic) CGFloat health;
#end
#implementation EnemyNode
- (instancetype)initWithColor:(UIColor *)color size:(CGSize)size {
self = [super initWithColor:color size:size];
if (self) {
self.health = 100.f;
}
}
- (void)getHit {
self.health -= 25.f;
}
- (BOOL)isDead {
return self.health <= 0;
}
#end
In your scene, you would use it as such:
EnemyNode *newEnemy = [[EnemyNode alloc] initWithColor:[UIColor blueColor] size:CGSizeMake(50,50)];
[self addChild:newEnemy];
...
[newEnemy getHit];
if ([newEnemy isDead]) {
[newEnemy removeFromParent];
}
For further illustration, you could take a look at my answer to a similar question.