(iOS) NSMutableArray as property addObject does nothing - objective-c

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.

Answer 2

Here's what your code will need:
#interface BlahBlah : UIViewController
#property (...) NSMutableArray *myArray;
#end
At first, *myArray is just a pointer that's equal to nil. You can't use this as an array yet. It needs to be set to a valid NSMutableArray instance. You need to do this in the designated initializer:
#implementation BlahBlah
#synthesize myArray;
// -initWithNibName:bundle: is the designated initializer for UIViewController
- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle
{
self = [super initWithNibName:nibName bundle:nibBundle];
if (self) {
myArray = [[NSMutableArray alloc] init];
// now you can add objects to myArray
}
return self;
}
- (void)dealloc
{
[myArray release];
[super dealloc];
}
Note that you can't just override -init; you must override the designated initializer for your class. Figure out what subclass you are implementing, find out what its designated initializer is, override that (but call the superclass implementation as is often necessary), then init your properties.
Here's Apple documentation regarding multiple/designated initializers.

Answer 3

#synthesis neither do alloc. So alloc and init your array. Then it should work.