How to inherit object and initialize : Objective-C - objective-c

Question

I created an object called Model that has some methods. I want to import Model into Mediator to use its methods there. But when I try to do this in Mediator.m I keep getting errors:
Initializer element is not a compile-time constant & No known class method for selector 'add'
I'm confused at to what these error are getting at. Researching them has not made things more clear.
Model.h
#interface Model : NSObject
#property (nonatomic) NSInteger tally;
-(int) add;
#end
Model.m
#import "Model.h"
#interface Model ()
#end
#implementation Model
- (instancetype)init
{
self = [super init];
if (self) {
self.tally = 0;
}
return self;
}
- (int)add {
self.tally = self.tally + 1;
return self.tally;
}
#end
Mediator.h
#interface MediatorController : NSObject
- (int)addOne;
#end
Mediator.m
#interface MediatorController ()
#end
#implementation MediatorController
Model *model = [[Model alloc] init]; <<<<<<< "Initializer element is not a compile-time constant"
- (int)addOne {
return [Model add]; <<<<<< "No known class method for selector 'add"
}
#end

Answer 1

First, you'll need a model property on your MediatorController
#interface MediatorController : NSObject
#property (strong, nonatomic) Model* model; //<-- Here
- (int)addOne;
- (int)subtractOne;
- (void)setValue:(int)value;
- (int)value;
#end
Then, you need an init method -- right now, you're trying to write your model = at the top level of the implementation, which doesn't work -- it needs to be inside a method.
Lastly, instead of calling add on Model (which is the class), call it on self.model, which is the instance of the class.
#implementation MediatorController
- (instancetype)init { //< -- Here
if (self = [super init]) {
self.model = [Model new];
}
return self;
}
- (int)addOne {
return [self.model add];
}
#end
You'll end up with a few compiler warnings because you haven't implemented the rest of the methods yet (subtractOne, setValue, etc), but this will get you started.