Question

Totally new to Obj-C, so thanks for patience. 😛

Because I’m beginner, I will use the car example. Easier for me to understand.

I have an object, Car. It has two member objects, tire and engine.

Tire and engine have their own member variables too, but they are just int with various names (like pressure, treadDepth).

In all these cases, I have synthesized accessor methods. I’m not sure about accessor methods for objects, so I just did @property id engine / @property id tire. Hope that is right!

Now, I can do dot.notation style to access like: [car.engine cylinders]. Fine! Sending tire and engine messages works fine. I write methods, this notation seems to work.

But when I declare an array of objects like 4 tires for the car:

@interface Car : NSObject {
     tire *tires[4];
}

I cannot send it message like this

[car.tire[0] setPressure: int];

It says accessing unknown tires getter method.

Basically I am wondering if someone can help me understand how to correctly access member variables of an object that is in an array.

Thanks!

Answer 1

You are trying to call a getter on car that doesn’t exist. You can’t return a C-style array by value anyway, so instead of just returning a Tire* pointer i’d rather use a NSArray in this case:

// header:
@interface Car : NSObject {
    NSArray *tires;
}
@property (nonatomic, copy) tires;
// ...

// source:
@implementation Car
@synthesize tires;

- (id)init {
    if ((self = [super init])) {
        tires = [[NSArray alloc] initWithObjects:
                  [[[Tire alloc] init] autorelease],
                  // ...
                  nil];
        // ...
    }
    return self;
}

- (void)dealloc {
    [tires release]; // don't forget to clean up
    // ...
}

Now you could use the getter:

[[[car.tires] objectAtIndex:0] setPressure:0];