Struggling with SKScene inheritance - objective-c

Question

I have a subclass of SKScene called SPGamePlayScene. It does a bunch of stuff. I need to make another scene that does the same stuff as SPGamePlayScene, but a little more/little differently, so I thought I would subclass my SPGamePlayScene for this new scene, SPPracticeScene. however im having issues with my class level instantiation methods.
below is the method of SPGamePlayScene:
//SPGamePlayScene.m
+ (instancetype)sceneWithSize:(CGSize)size colored:(BOOL)colored {
SPGamePlayScene *gamePlayScene = [SPGamePlayScene sceneWithSize:size];
gamePlayScene.colored = colored;
gamePlayScene.backgroundColor = [SKColor whiteColor];
return gamePlayScene;
}
this works fine. However in my subclass of SKGamePlayScene, SPPracticeScene, I need to create an SPPracticeScene object using its super class's sceneWithSize colored method.
//SPPracticeScene.m which inherits from SPGamePlayScene
+ (instancetype)sceneWithSize:(CGSize)size {
//this keeps giving me a SPGamePlayScene but I need it to be a SPPracticeScene
SPPracticeScene *practiceScene = (SPPracticeScene *)[self sceneWithSize:size colored:NO];
//this line throws an exception because practiceHud is not a property of SPGamePlayScene
practiceScene.practiceHud = [SPPracticeHud practiceHudAtPosition:CGPointMake(0, practiceScene.frame.size.height - 20) inClef:[SPGameState sharedInstance].clef inFrame:practiceScene.frame];
[practiceScene addChild:practiceScene.practiceHud];
return practiceScene;
}
I know that this returns an SPGamePlayScene so I tried casting it with no luck. The line that sets the practiceHud property causes a crash since SPGamePlayScene does not have that property (even though its supposed to be an SPPracticeScene. This is my first foray into custom subclasses/inheritance so im probably misunderstanding something about the way things need to be done/what types need to be returned etc. How can I make this work?

Answer 1

I ended up just overriding the initWithSize method and using an instance level initializer instead of a class level one. using an init method returning an id seemed to do the trick.
//SPGamePlayScene.m
(id)initWithSize:(CGSize)size colored:(BOOL)colored {
if (self = [super initWithSize:size]) {
//some custom code here
}
return self;
}
//SPPracticeScene.m which inherits from SPGamePlayScene
- (id)initWithSize:(CGSize)size {
//init it using the SPGamePlayScene custom initializer
if (self = [super initWithSize:size colored:NO]) {
//some custom code here
}
return self;
}
using the above code let me use the custom initializer for SPPracticeScenes super class, but add additional functionality to it that I needed, while making sure the object returned was of the correct type. I would love to know how I could have made it work with my class level initializers though.