Question

I have a subclass of UIViewController with an NSMutableArray as a property to use as the data source for a UITableView. I create an instance of the class in my storyboard.

I want to populate the array with the addObject: method but if I try, the array always returns (null).

I read that @synthesize doesn’t init the array and I might need to override -init and init the NSMutableArray there but -init never gets called.

How is this supposed to work?

Answer 1

You need to create an instance of NSMutableArray and assign it to the property.

Since the object with the property is a UIViewController created in a storyboard, you can do it in a few different places. You can override initWithCoder:, or awakeFromNib, or viewDidLoad.

If you override initWithCoder:, it is imperative that you call the super method.

If you do it in viewDidLoad, the array won’t be created until the view is loaded, which doesn’t have to happen right away.

I recommend doing it in awakeFromNib:

@synthesize myArray = _myArray;

- (void)awakeFromNib {
    _myArray = [[NSMutableArray alloc] init];
}

Another option is to just create the array lazily by overriding the getter method of the property:

@synthesize myArray = _myArray;

- (NSMutableArray *)myArray {
    if (!_myArray)
        _myArray = [[NSMutableArray alloc] init];
    return _myArray;
}

If you do this, it is very important that you always access the array using the getter method (self.myArray or [self myArray]) and never by accessing the instance variable (_myArray) directly.